shoulder lesions in danish sows
TRANSCRIPT
SHOULDER LESIONS IN DANISH SOWS - an abattoir survey with emphasis on the relation between
clinical signs and post-mortem registrations
VETERINARY MASTER THESIS 2007
(27 ECTS POINTS) Supervisor:
Professor Jens Peter Nielsen Institute of Production Animals and Horses, Faculty of Life Sciences, University of
Copenhagen Veterinary student: Jens Strathe V9105
Post-mortem findings
Ante-mortem, clinical signs
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Preface _____________________________________________________ The project in hand constitutes the work accomplished in relation to my Veterinary Master Thesis at
the Faculty of Life Science, KU. The subject is shoulder lesions in sows with emphasis on clinical
signs as marker of pathological shoulder lesions and it addresses veterinarians for use in advisory
situations on farms and veterinary students with special interest in this subject.
The project came to surface based on an idea by Professor Jens Peter Nielsen, Institute for
Production Animals and Horses. I would like to express my gratitude for his great effort and
inspiration in the creation of this project, also willingly founding and providing the means that made
the data-collection possible.
I would like also to express thanks to Professor Anders Ringaard Kristensen, Institute for
Production Animals and Horses, who provided more help and assistance than could be expected to
the data analysis and especially to the construction of a Bayesian Network.
A special thanks to my brother, PhD student Anders Strathe, for his many hours allocated to our
statistical discussions and for solving recurring problems with SAS, often very late in the evening.
Thanks to PhD student Mogens Krogh for inspiring conversations and help during the 5 months of
office-sharing.
Also collected thanks to Klaus Hedeman Pedersen and Anders Strathe for their participation with
great spirit and enthusiasm in the abattoir-survey which brought insomnia, hard work but also great
fun during the two weeks of data-collection.
Great thanks to all employees at the abattoir in Skærbæk; veterinarians, technicians and abattoir-
workers in the stables for most kindly helping and providing practical solutions to a great many
problems.
Thanks to my mother Hanne Wiik Christensen for a thorough review and to stud.med.vet Gitte
Madsen for her help with layout and great patience with me personally during the process of writing
my Master Thesis.
Copenhagen, January 2007
_________________________
Jens Strathe V. 9105
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Summary _____________________________________________________ An abattoir survey with emphasis on the relation between clinical signs and post-mortem
registrations was carried out in a two week period during November 2006. The prevalence of
clinical findings by ante-mortem examination and of post-mortem grading of shoulder lesions was
calculated. A stochastic biological model for pathological shoulder lesions was built using a
Bayesian network approach. Shoulder lesions post-mortem was modelled based on clinical findings
from ante-mortem investigation and body condition. The mandatory meat-inspection was evaluated
by comparison with detailed post-mortem examination of notifiable shoulder lesions (Golden
Standard).
A literature study reviews the subject of shoulder lesions.
Following conclusions have been established;
Collectively, the prevalence of notifiable shoulder lesion cases was 1.93%. The lower grade
shoulder lesion cases (grade one and two) were more difficult to detect at ante-mortem examination
than post-mortem since 39 cases (30 grade one- and nine grade two lesions) were found only at
post-mortem examination. However, all notifiable cases was detected at ante-mortem, and they
were described by approximately the same clinical symptoms (skin alteration and firm swelling that
is adherent by palpation).
Results from the stochastic model showed that when undertaking clinical examination of shoulder
lesions, the condition of the skin (crust/scar) in itself was of little value if not compared with the
palpable findings in the tissue underneath where especially adherence to the underlying bony
foundation (tuber spina scapula) and firm large swellings were the best markers of notifiable
pathological lesions (grade three and four).
Most probable markers of reportable shoulder lesions are;
Firm swellings with a fair extent (>50 mm in width)
Adherence of lesions to the underlying bony foundation
Crusting and erythema only when overlaying larger firm lesions
A fairly high sensitivity, 80% with a confidence interval [55.7; 93.4] and a high specificity, 97%
with a confidence interval [95.2; 98.7] was found for the mandatory meat-inspection when
diagnosing notifiable shoulder lesions. Keywords: Sows, shoulder lesions, clinical markers of notifiable shoulder lesions, mandatory meat-inspection and
shoulder lesions.
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Sammendrag _____________________________________________________ Formålet med dette speciale var at beskrive mulige sammenhænge mellem kliniske fund og post-
mortem patoanatomisk graduering baseret på materiale fra 14 dages slagtninger af søer i november
2006. En stokastisk biologisk model for skuldersår er konstrueret i et Bayesiansk netværk, hvor
post-mortem graduering er modelleret på baggrund af evidens om kliniske fund ved ante-mortem
undersøgelse og risikofaktoren visuelt huld.
Prævalens er beregnet for kliniske fund ved ante-mortem undersøgelsen og den post-mortelle pato-
anatomisk graduering, og endelig er kødkontrollen evalueret i forhold til detaljeret post-mortem
undersøgelse som golden standard.
Et litteratur-studie belyser emnet skuldersår hos søer.
Følgende konklusioner drages fra specialet;
Den samlede prævalens for anmeldepligtige skuldersår var 1,93% (grad tre og fire). De lavgradige
skuldersår (grad et og to) var sværere at detektere ved klinisk undersøgelse end ved post-mortem
patoanatomisk undersøgelse, eftersom 39 tilfælde (30 grad et- og ni grad to skuldersår) udelukkende
blev fundet ved post-mortem undersøgelse. Alle anmeldepligtige skuldersår blev fundet ved den
kliniske undersøgelse, og de var beskrevet med stort set de samme symptomer (hudforandring, fast
og adherent hævelse).
Resultater fra det Baysianske netværk viste, at når skuldersår undersøges klinisk, er huden
(ar/skorpe) i sig selv ikke nogen særlig god markør for anmeldepligtige skuldersår, hvis ikke
fundene sammenholdes med de palpatoriske fund i de underliggende væv, hvor særligt
uforskydelige læsioner og større faste hævelser er egnede markører for anmeldepligtige skuldersår.
Egnede markører er;
Faste hævelser af en rimelig størrelse (>50 mm i diameter).
Uforskydelige læsioner i de dybereliggende væv.
Skorpe og rødme, hvis de er ledsaget af underliggende palperbare faste hævelser.
En forholdsvis høj sensitivitet, 80% med konfidensinterval [55,7; 93,4] og en høj specificitet, 97 %
med konfidensinterval [95,2; 98,7] blev fundet ved sammenligning mellem kødkontrollens
påvisning af anmeldepligtige skuldersår og en detaljeret pato-anatomisk undersøgelse post-mortem
(grad 3 og 4). Nøgleord: Søer, skuldersår, kliniske markører for anmeldepligtige skuldersår, kødkontrol og skuldersårs dianogstik.
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Table of contents ____________________________________________________________
1. INTRODUCTION ........................................................................................................................................................ 5 2. LITERATURE-STUDY ............................................................................................................................................... 7
2.1 INTRODUCTION ......................................................................................................................................................... 7 2.2 ANATOMY OF THE SHOULDER - (A SHORT OVERVIEW) .............................................................................................. 7 2.3 PATHOGENESIS OF DECUBITAL ULCERS..................................................................................................................... 8
2.3.1 Patophysiologic response to sustained pressure .............................................................................................. 9 2.3.2 Relationship of pressure–duration and ancillary externalfactors.................................................................. 10 2.3.3 Development of pressure ulcers –“top- to- bottom” or “bottom-to-top” ...................................................... 12
2.4. ANIMAL-LEVEL RISK FACTORS OF SHOULDER LESION DEVELOPMENT.................................................................... 13 2.5 CLASSIFICATION OF SHOULDER LESION................................................................................................................... 15 2.6 SHOULDER LESION IN MANDATORY MEAT INSPECTION DATA.................................................................................. 16 2.7 SHOULDER LESION IN EXTENDED MEAT-INSPECTION SURVEYS ............................................................................... 18
3. AN ABATTOIR SURVEY WITH EMPHASIS ON THE RELATION BETWEEN CLINICAL SIGNS AND POST-MORTEM REGISTRATIONS.......................................................................................................................... 20
3.2 INTRODUCTION ....................................................................................................................................................... 20 3.2.1 Background .................................................................................................................................................... 20 3.2.2 Objectives of the present abattoir survey ....................................................................................................... 20
3.3 MATERIAL AND METHODS....................................................................................................................................... 21 3.3.1 Study design ................................................................................................................................................... 21 3.3.2 Sampling methods .......................................................................................................................................... 23 3.3.3 Sample size ..................................................................................................................................................... 24 3.3.4 Descriptive and statistical analysis ................................................................................................................ 24 3.3.4.1 The prevalence study................................................................................................................................... 24 3.3.4.2 The study of clinical signs as marker for pathological sholder lesions (Bayesian net)............................... 25 3.3.4.3 Evaluation of inter-observer agreement...................................................................................................... 29 3.3.4.4 Sensitivity and specificity of the diagnosis “notifiable shoulder lesions”................................................... 29
3.4 RESULTS ................................................................................................................................................................. 29 3.4.1 The prevalence study...................................................................................................................................... 29 3.4.2 The study of clinical signs as marker for pathological sholder lesions (Bayesian net).................................. 33 3.4.3 Evaluation of inter-observer agreement......................................................................................................... 36 3.4.4 Valuable clinical signs as marker of pathological shoulder lesions .............................................................. 37 3.4.5 Sensitivity and specificity of the diagnosis “notifiable shoulder lesion” ....................................................... 37
3.5 DISCUSSION ............................................................................................................................................................ 37 3.5.1 The prevalence-study...................................................................................................................................... 37 3.5.2 The study of clinical signs as marker for pathological shoulder lesions (Bayesian net)................................ 39 3.5.3 Evaluation of inter-observer agreement......................................................................................................... 40 3.5.4 Valuable clinical signs as marker of pathological shoulder lesions .............................................................. 40 3.5.5 Sensitivity and specificity of the diagnosis “notifiable shoulder lesion” ....................................................... 40
3.6 CONCLUSION .......................................................................................................................................................... 41 3.7 PERSPECTIVES......................................................................................................................................................... 42
4. REFERENCES ........................................................................................................................................................... 43 5. ENCLOSURES
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1. Introduction
__________________________________________________________ The Danish swine production industry meets increasing demands from the public with regards to
the welfare of our production animals, transparency and the level of food safety.
Great public- and legislative interest has focused on the chronic injures related to shoulder lesions
of sows.
From 2001 and onwards, shoulder lesions have been recorded by a separate code at the abattoirs in
order to obtain better estimates of the scope related to the problem. From 2003 shoulder lesions of a
certain severity (degree 3 and 4) were reportable to the police and resulted in legal actions against
producers having sows on farm or sending sows to the abattoir with these lesions – this practice was
based on recommendations from a central authority (Det Veterinære Sundhedsråd, 2003). Also,
veterinarians were responsible by law to report these lesions to the police when found on farm,
because they were from this point in time interpreted as a violation of the legal protection of
animals (Anonymous, 2005).
It has been reported that it is not always possible to determine the degree and thereby gravity of the
chronic skin lesions by clinical inspection and palpation (Jensen and Svendsen, 2006). In this
context the wound can be undermined and be more extensive than the mere penetration of the skin
shows. This makes it possible that totally- or partially healed shoulder lesions at ante-mortem
registration can break up during transportation to abattoirs or during the slaughtering process and
give rise to more serious judgement than what was possible ante-mortem (Jensen and Svendsen,
2006)
The focus of this Master Thesis was the association between clinical recordings and pathological
lesions. The thesis includes a literature study in which I focus on the pathogenesis of decubital
ulcerations in humans and in pigs for comparative reasons. Subsequently the focus will be on
existing classification and current problems related to the classifications of shoulder lesions in sows.
Finally, findings in previous surveys on shoulder lesions in mandatory meat inspection data and
extended meat inspection surveys are reported.
The second part of this Master Thesis is a field study on shoulder lesions of culled sows sent to
slaughter at an abattoir of sows in Skærbæk, Jutland.
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In the following, shoulder lesions of grade three and four will be denounced “notifiable shoulder
lesions” meaning that they are reportable to the police by law, even though the use of the word
“notifiable” normally refers to conditions reportable to the veterinary authorities.
The objects of the abattoir survey were the following:
1) To estimate clinical and pathological prevalence of shoulder lesions and to evaluate possible
association between subcutaneous layer of fat and shoulder lesion prevalence.
2) To construct a stochastic biological model for prediction of probabilities for pathological
shoulder lesions (notifiable) using a Bayesian network by including relevant risk factors and
evidence of clinical signs of sows examined both ante- and post-mortem.
3) To deduce from the model combinations of simple clinical signs as marker of pathological
shoulder lesions for veterinarians in an advisory situation.
4) To estimate sensitivity and specificity of the diagnosis “notifiable shoulder lesion” of sows by
the mandatory meat inspection according to the detailed post-mortem examination (Golden
Standard).
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2. Literature-study ____________________________________________________________
2.1 Introduction The skin, or integument, is the single largest organ of the body, representing the physical barrier
between the environment and the organism (Jones et al., 1997). The skin can reflect a wide variety
of disorders, therefore examination of the skin constitutes a key component of any thorough
physical examination (Arundel and Radostits, 2000).
The skin response to injury depends upon where the inciting injury occurs, the type and nature of
the insult, and the duration, location to specific skin structures, and severity of the inciting agent
(Jones et al., 1997).
The most frequent sites for decubital ulcers are areas of skin overlying bony prominences (Edlich et
al., 2004). In sows, they especially develop in the area overlying the tuber of the spine of scapula (s.
Tuber Spina Scapula), and the lesions are similar to bedsores in people who are confined to a bed or
wheelchair (Zurbrigg, 2006). The paticular anatomy of the shoulder blade of sows (pigs in general)
is partly suspected as the reason why this area is more affected with regards to decubital ulcers than
other areas of the body of sows (se next section).
2.2 Anatomy of the shoulder - (a short overview) Os scapulae (number 14, figure 1) is the bone-related foundation in the shoulder region of sows on
which pressure ulcers develop (Lund, 2003). The lateral surface is divided by a centrally placed
ridge (s. Spina Scapula) which also demarks the two fossae in which M. infraspinatus og M.
supraspinatus lie (Dantzer and Schauser, 1995).
Tuber spinae scapulae (number 15, figure 1) is a bony prominence lying superficially on the
centrally placed ridge (s. Spina scapulae) and the prominence is shaped like a tongue and drawn
caudally (Dantzer and Schauser, 1995).
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Figure 1: Two young sows. Os scapulae (14) and Tuber spina scapulae (15). The insert is modified from Dyce, Sack and Wensing 1996.
This anatomical shape of scapula is a special feature of the pig scapula (Constantinescu and
Schaller, 1992b) and because it is the highest part of the bone and sticks farthest out, the spine and
its prominence bear the most weight when the sow is lying down (Reese et al., 2005). This latter
feature is also a subject of interest when considering the muscular fill of the shoulder blade.
The two muscles (M. infraspinatus and M. supraspinatus) give total fill to the corresponding fossae
on the shoulder blade as mentioned before (Constantinescu and Schaller, 1992a; König et al., 2005).
The deltoid muscle (s. M. deltoideus) has it origin on the spine of scapula as an aponeurosis which
gives it very little muscular fill over scapula contrary to other species (König et al., 2005). On these
grounds and because of the superficial placing of the tuber this part of the shoulder blade is a locus
of minor resistance in relation to damage pressure induced because of the lack of soft tissue to
disperse the pressure from deforming loads (Bader, 1990; Jensen and Svendsen, 2006).
2.3 Pathogenesis of decubital ulcers In the following, shoulder lesions of sows defined as decubital ulcers will be referred as “pressure
ulcers” in order to make comparisons between human and veterinary research and in this respect to
avoid confusion on the nomenclature. Reference will be made to studies from human medicine in an
effort to elucidate this very large and complex subject; it is moreover done with emphasis on
possible comparative aspects and because there are many similarities in skin properties between
swine and humans regarding physiological structure and function of the skin (Kokate et al., 1995).
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Also the skin of man closely resembles the skin of swine histologically which makes swine a good
model of human pressure ulcers (Dinsdale, 1974) and visa versa. Aditionally, many of the studies
on pressure/duration have been carried out on pigs.
The following definition of pressure ulcers is obtained from human medicine;
“Pressure ulcers are areas of unrelieved pressure over a region of skin
resulting in ischemia, cell death and tissue necrosis” (National Pressure Ulcer Advisory Panel, 1989)
Different reasons have been suggested in order to describe the basic patophysiologic response that
leads to soft tissue breakdown. The next section will present different theories.
2.3.1 Patophysiologic response to sustained pressure Theories describing the response leading to soft tissue destruction from pressure application
involve localized ischemia due to blood vessel occlusion, impaired interstitial fluid flow and
lymphoid drainage, reperfusion injury and sustained deformation of cells (Bouten et al., 2003).
Focusing on the microcirculation, the effect of compressive forces is a disruption of capillary blood
flow and obstruction of the contractile lymph flow which leads to a loss of nutrients to the
compressed tissue and an accumulation of metabolic waste products (Shea, 1975; Miller and Seale,
1981). An increased rate of cell death ensues, and eventually the tissue suffers necrosis (Bansal et
al., 2005).
The theory on reperfusion injury focuses on the damage induced when blood circulation restores
after pressure removal through oxygen-free radicals (Herrman et al., 1999). The mechanism
suggested should be the same as described for other postischemic pathologies such as cardiac
infarction, however, the specific role of reperfusion injury in pressure ulcers remains unclear
(Bouten et al., 2003).
By evaluating histological data, a cellular origin to pressure sore development has been put forward
(Landsman et al., 1995). Sustained cell deformation due to sustained pressure application on soft
tissue leads to cellular damage (volume changes and cytoskeletal reorganisations) which may be an
early component of tissue breakdown (Landsman et al., 1995).
Finally, with emphasis on the theory of ischemia, a theory states that moderate point pressure over
bony prominences both distracts and compresses the tissues which in an extended state leads to
rupture of many venules and capillaries around the area of maximal pressure whereby multiple
thrombi form inducing ischemia (Lowthian, 2005). The biomechanical forces induced when
pressure is applied to the skin surface is comparable with a gel (see figure 2) spreading sideways
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when squeezed (Lowthian, 2005). The matter of biomechanics will be further adressed in the next
section.
Figure 2: Soft tissue under external pressure illustrated by a compressed gel which clearly shows the stretching forces
within the gel as it is put under pressure. Modified from (Lowthian, 2005).
2.3.2 Relationship of pressure–duration and ancillary external factors On the grounds, many different studies have been made related to the relationship of pressure
duration in order to elucidate the minimal amount of pressure applied to a skin surface, especially
over a bony prominence that will lead to pressure ulcer development.
Kosiak (1959) concluded that an inverse relationship exists between pressure applied to the skin
surface and duration with histological changes occurring after 60 mmHg pressure for 1 hour on the
femoral trochanter and ischial tuberosity of mongrel dogs.
In a survey by Daniel et al. (1981), a critical pressure duration curve for pressure sores was
presented for normal swine. Muscle damage occurred at a high pressure short duration (500 mmHg,
4 hours), whereas skin destruction required high pressure long duration (800 mmHg, 8 hours). They
concluded that muscle is more sensitive to the effect of pressure than skin and that the initial
pathological changes occur in muscle and subsequently progresses towards the skin with increasing
pressure and/or duration.
Le et al. (1984) went beyond the study of interface pressure at skin level. Their recordings focused
on in tissue pressure measurements and brought to knowledge the very important fact that although
the external pressure stays below the capillary pressure (25-30 mmHg), the internal pressure can be
three to five times greater than what would induce pressure ulcer if not relieved. The conclusion
was that tissue pressure increases with proximity to bony prominences in both depth and lateral
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distance with the implication that pressure sores starts near bony prominences and progresses
outwards - also in accordance with Daniel et al. (1981). See figure 3 for visual understanding of the
biomechanical conditions in soft tissue under pressure.
The discussion of pressure ulcer development concerning the direction of soft tissue destruction -
“top- to- bottom” or “bottom-to-top” (Jensen and Svendsen, 2006), will follow.
Figure 3: A model of the differential response of different soft tissue as pressure is applied. The arrows indicate areas
of high stress (a man is seated on a cushion). Modified from (Bouten et al., 2003).
Pressure and duration have not alone been able to account for the development of pressure ulcers.
Other external factors (friction, repetitive pressure and/or moisture) have proven an additive effect
on the development of pressure ulcers whereby the pressure duration threshold of tissue breakdown
is lowered. A study concluded that friction increases the susceptibility to skin ulceration at constant
pressure less than 500 mmHg which was considered an important finding in a clinical situation (in
relation to human pressure ulcers) since pressure at skin level under practical conditions seldom
exceeds 500 mmHg (Dinsdale, 1974). Adding the effect of repetitive pressure to friction lowers the
threshold for ulcer development to mere 45 mmHg (Dinsdale, 1974).
In a study on skin-blood flow occlusion, the combination of pressure plus shearing force (shearing
force = static friction as defined by Lowthian (2005)) shows particularly efficient as the necessary
value of pressure to cause occlusion is nearly halved when accompanied by sufficient shear
(Bennett et al., 1979).
The effect of temperature and pressure ulcer development has also been shown (Kokate et al.,
1995). Keeping pressure/duration at constant levels (100 mmHg applied for five hours) and varying
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the temperature of the pressure points shows that only deep tissue damage is the result when
pressure is applied at 35 degrees C. At 45 degrees C there is full thickness cutaneous- and deep
tissue injury. However, the application of 25 degree pressure points shows no signs of injury,
suggesting that injuries may be preventable by temperature modulation (Kokate et al., 1995).
2.3.3 Development of pressure ulcers –“top- to- bottom” or “bottom-to-top” The different animal studies on pressure duration studies all suggest an inverse relationship between
the magnitude of pressure and the duration suggesting that pressure ulcers can develop either
superficially and progress in depth or develop from within the deep tissue near bony prominences
under intact skin and move outward (Bouten et al., 2003).
The theory on pressure ulcers developing from “top-to-bottom” is based on work by Shea (1975),
stating that an orderly progression from a superficial- to a full-thickness lesion through step-wise
detoriation can begin with minor ulcerations and eventually involve deeper tissue. Witkowski and
Parish (1982) supports the same explanation. Determining factors of the “top-to-bottom” model are
removal of stratum corneum which subjects the epidermis to infection (Dinsdale, 1973) and lack of
pressure relief (Bader, 1990).
Closed deep ulcers presume the “bottom-to-top” model of ulcer development. The soft tissue injury
begins in the deep soft tissue (especially muscle) covering bony prominences. Later on it progresses
superficially to penetrate through the skin as an ulcer (Jørgensen, 2004). This implicates that
considerable necrosis of muscle, fascia and subcutaneous tissue can occur even at a stage when the
skin only shows minor signs of tissue breakdown (Bouten et al., 2003). As earlier mentioned, this
has been reproduced in animal experimental models with pigs over the greater trochanter of femur
(Daniel et al., 1981; Le et al., 1984).
However, the prevailing theory on pressure ulcer development in the shoulder region of sows is
stated by Jensen and Svendsen (2006). It has its point of reference in a model compatible with the
“top-to-bottom” development. The theory is based on evidence of histological evaluation of 546
random sampled pressure ulcers of different grades from shoulder blades of culled sows sent to
slaughter (classification of pressure ulcers will be reviewed in the next section). They state two
important findings supporting their theory;
1. They did not find more severe forms of pressure ulcers in sows (grade three and four as
defined by Lund (2003)) associated with infectious osteitis or necrosis of the underlying
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bone of which the authors refer as a regular finding in grade four human pressure ulcers
when developing from underlying bony prominences (“bottom to top”).
2. For all examined severe cases of pressure ulcers (grade 3 and 4) excessive
granulation/connective tissue are always found – towards the surroundings and towards the
bone at the wound base. The periosteal reaction as well as the granulation tissue is initiated
by an overlying inflammatory process progressing from top and downward.
In a paper by Lund (2003) on 174 histological evaluations on pressure ulcers as part of his Master
Thesis, made as an extended meat-inspection survey, the conclusion on an “top-to-bottom”
pathogenesis was in agreement with Jensen and Svendsen (2006), stating that a progressing
development was evident. In the latter survey, muscular damage was found in the histological
samples but without sign of early involvement which was anticipated due to the muscle being an
ischemia-sensible tissue (Le et al., 1984; Bosboom et al., 2001). Lund (2003) explains the latter
finding by the special anatomy of the sow in the shoulder region with respect to the sparse muscular
fill around the tuber. Importantly, the theory of pathogenesis stated by Lund (2003) and supported
by Jensen and Svendsen (2006) conditions that the caretakers of sows at all times are aware of the
of the extent of ulcer development and thereby legally responsible (Anonymous, 2005).
It appears that there is diverging evidence of the pathogenesis of these pressure ulcers. It was shown
in previous pressure duration experiments (Daniel et al., 1981; Le et al., 1984) on swine that closed
deep pressure ulcers with a “bottom-to-top” development can be inflicted by pressure application to
pig skin over the greater trochanter of femur. This implies that when erythema of the skin is
evident, there a large undiscovered lesion is lurking in the deep tissue overlaying the bone.
2.4. Animal-level risk factors of shoulder lesion development Epidemiologic studies performed on farms have shown environmental effects (type of housing,
flooring, herd size etc.) in relation to the development of shoulder lesions. In this section the focus
will be on factors of the sow in relation to shoulder lesion development. The aim of this effort is to
narrow down the study of this extensive area of research.
Shoulder lesion of sows over the tuber of the spine of scapula (tuber) is a multifactorial condition
affecting postparturient sows and developing in the time after farrowing (Davies et al., 1997;
Christensen et al., 2002; Havn et al., 2004; Zurbrigg, 2006). A peculiar feature is the finding by
several authors that shoulder lesion develops more commonly on the right shoulder than the left one
(Davies et al., 1996; Davies et al., 1997; Lund, 2003). This finding indicates that sows may have a
preferential recumbency on the right shoulder since the depth of soft tissue over the tuber (tuber
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depth) does not differ between left and right shoulders of sows (Davies et al., 1997). Lund (2003)
has found in an extended meat-inspection study that 149 sows of 397 with shoulder lesions have
bilateral lesions (37,5%). The bilateral appearance was according to the degree of the ulcer on one
side, indicating that sows somehow alleviated their affected shoulder to some extend when
developing to much on one side.
Lowered body condition has been found to be a risk factor of pressure ulcer development in several
studies on live animals evaluated by visual inspection (Davies et al., 1996; Havn et al., 2004;
Rosendahl and Nielsen, 2004) and back fat measure (Davies et al., 1997). In studies on slaughtered
sows by extended meat-inspection surveys, an effect of back fat depth was found by Christensen et
al. (2002) stating that for each 1 mm extra back-fat depth, the risk of pressure ulcers has decreased
by a factor 0,84. Their theory is that a good back-fat depth is equivalent to a good padding over the
tuber and thereby preventive against shoulder lesion. Davies et al. (1997) found that body condition
score, back fat depth and tuber depth are all significant risk factors of shoulder lesion, however they
are also highly correlated. They concluded that the amount of soft tissue overlaying the tuber is the
direct determinant for the risk of developing shoulder lesion in sows, whereas visual body condition
score and back fat depth is considered as proxy measures.
An effect of parity on the risk of development of shoulder lesion has been shown in several studies
(Davies et al., 1997; Christensen et al., 2002; Zurbrigg, 2006). A common explanation by different
authors is that older sows have higher body weight, are larger-framed with more limited movement
in the farrowing crates and therefore experience more pressure induced damage over the tuber.
However, the parity effect cannot totally be explained by weight and being large-framed because
there seems to be a cut of point where heavy weight becomes protective against developing a lesion
(Zurbrigg, 2006). Christensen et al. (2002) stated that the cut-off point of weight being protective
also may have been an effect of large and heavy animals remaining active as breading animals for a
longer period of time due to good health status and probably also due to not having shoulder
lesions. Finally, it has been shown that sows with old pathological shoulder lesions are predisposed
to development of new lesions in the following nursing periods (Davies et al., 1997; Christensen et
al., 2002).
Other factors have been assigned to the list of risk factors of shoulder lesion development - factors
predisposing the sow to more prolonged recumbency. Havn et al. (2004) suggested general
periparturient disease as metritis, mastitis and agalctia (MMA). Others have claimed an effect of
lameness which makes the sow less reluctant to stand up (Bonde et al., 2001). Finally, the
15
temperament of the sow and her activity around farrowing has been stated as a risk factor, where
sows that are predominantly lying down or otherwise uneasy have increased risk of developing
shoulder lesions (Nielsen and Vestergaard, 2003).
2.5 Classification of shoulder lesion The existing Danish classification system on shoulder lesions of sows is created by Lund (2003).
His grading scale is based on human grading scales developed on the basis of work done by Shea
(1975). These human grading scales are sequential clinical descriptions of soft tissue ulceration
caused by pressure and are used to identify and measure the severity of tissue damage (Pedley,
2004).
The scale by Lund (2003) was created in order to make standardized registrations on shoulder
lesions macroscopically on slaughtered sows and to create the necessary foundation of a forensic
decision in cases of animal welfare matters regarding the severity of shoulder lesions of sows.
The scale was constructed as a simple scale with five degrees (0-4), all substantiated by histological
evidence in order to secure a rapid and precise registration with the different grades reflecting the
impact on the animal in question (Lund, 2003). The grading scale is presented in table 1 translated
from Danish. Table 1 The morfological grading of shoulder lesion in the shoulder region of sows*
Grade Description
0 No lesions of the skin
1 The lesion is limited to the epidermis, eventually with a moderat crust.
2 The lesion involves the dermis, eventually with extensive crusting. There is little fibrosis and/or
granulation tissue.
3 The lesion penetrates to the subcutis. There is intense formation of granulation tissue
4 Ulcer penetrating to the bone or ulcer development with periosteal bony proliferation.
*By Lund (2003), modified from Jensen and Svendsen (2006).
To accurately use the scale described above the damaged tissue layers including the wound bed has
to be identified in order to make a correct grading. This may impose difficulties because the lesions
in themselves may reflect a mixture of different ulcerstages due to the fact that they often are
untreated lesions, results of repeating trauma and regenerative processes and to some extent
contaminated and concealed by debris and crusting (Lund, 2003). Furthermore, the slaughtering
process may obscure the outlines of each tissue layers.
16
However, on a detailed post-mortem patho-anatomical investigation, transection of the lesion down
to the tuber of the spine of scapula gives a fairly accurate knowledge of the extent to which the
lesion is penetrating and whether the bone is affected (Jensen, 2006).
Grading of shoulder lesions by ante-mortem inspection is more problematic. By simple visual
inspection and palpation the extend of the wound and thereby the grade of lesion may be hard to
determine due to the above mentioned reasons (crusting, debris etc.). Also undermining of the
lesion conceals a larger extend of a lesion than indicatedly the mere skin penetration (Jensen and
Svendsen, 2006).
Another problem concerning ante-mortem grading is that many of these lesions heal by second
intention and leave thin, friable scars that have a tendency to break open when strained (Nielsen and
Vestergaard, 2003). Therefore, these undermined, partially or completely healed shoulder lesion
sometimes appear more severe on post-mortem evaluation (due to the slaughtering process) than
what was found by ante-mortem examination (Jensen and Svendsen, 2006). Basically, there is a
problem with ante-mortem examination of sows with shoulder lesion, especially in relation to basic
clinical signs predicting the more severe lesions post-mortem (grade three and four). So far, no
studies have been conducted on the correlation between ante-mortem clinical findings and detailed
post-mortem pato-anatomical findings. As a final statement regarding the use of grading scales, one
has to bear in mind that they are open to bias and subjectivity due to individual interpretation which
reflects user knowledge and clinical ability to identify anatomical structures and relevant clinical
changes – all aspects which make grading scales vulnerable to low levels of inter-rater reliability
(Pedley, 2004).
2.6 Shoulder lesion in mandatory meat inspection data In an effort to determine the prevalence of shoulder lesions on a national scale and on a vast number
of slaughtered sows, a number of studies have been made by collecting the specific meat inspection
data on shoulder lesions from the largest abattoirs in Denmark. Table 2 presents the results from
different surveys of meat inspection data related to shoulder lesions.
17
Table 2 Results from studies on prevalence of shoulder lesions in mandatory meat-inspection data. Author Year/period of
registration
Abattoir Number of sows
recorded
Prevalence of
shoulder lesion
(Cleveland Nielsen et
al., 2004)1
Whole year of 2000
Four different abattoirs.
23.794
7,3 %
(Christensen et al.,
2002)
1.half year of 2001
1.half year of 2001
Sæby
Skærbæk
57.082
105.113
3,41 %
5,22 %
(Christensen, 2003)
1/7 2002 to 1/7 2003
Sæby
Skærbæk
133.747
241.201
6,86 %
4,4 %
(Christensen et al.,
2004)
1/1 2002 to 1/7 2003
Three different abattoirs.
620.000
4,3 %
(Overall abattoir adjusted prevalence )2
1 Until the last quarter of 2000 there was no separate registration of shoulder lesion, but it was included in the general registration of all decubital lesions on the carcasses of slaughter sows. However, Christensen et al. (2002) showed in a study performed in 2001 that for the two abattoirs of Sæby and Skærbæk the shoulder lesions accounted for 78% and 64 % of all recorded decubital lesions. The data of Cleveland Nielsen are therefore with a little approximation representative. The prevalence presented includes all registered decubital lesions including shoulder lesions. The prevalence is adjusted for abattoir-effect. 2 Recordings have been done on approximately 20.000 sows sent to both Sæby and Skærbæk – all the sows delivered to the two abattoirs were from the same farmers who, over a period of a year, sent >50 sows to both abattoirs. The result was that the Sæby-abattoir only registered 69% of the shoulder lesions of what Skærbæk did (Christensen, 2003). The overall prevalence is therefore balanced according to the abattoir effect.
From table 2 large variations in estimated prevalences have been found between abattoirs which
among others reflects different sensitivities on the mandatory meat-inspection.
In a study comparing ante-mortem examination to the mandatory meat-inspection in relation to
detecting shoulder lesions a total of 747 sows were examined, 75 (~10%) had shoulder lesions
(Christensen, 2003). In table 3 a part of the survey is presented - 685 sows totally including 13
severe cases of shoulder lesions found by ante-mortem examination. Severe cases were defined as
sows having either a lesion penetrating to exposed bone or a swelling with an extend of more than
10 mm of vertical distance from the shoulder blade (Christensen, 2003).
18
Table 3. Sensitivity and specificity of diagnosing shoulder lesions by mandatory meat-inspection compared to ante-mortem examination. Severe cases No findings Total
Meat-inspection remark + 7 1 8
Meat-inspection remark - 6 671 677
Total 13 672 N= 685
Sensitivitet (%) = 53,84 %
Specificitet (%) = 99,85 %
Modified from (Christensen, 2003) A quite low sensitivity by the mandatory meat-inspection on shoulder lesions was detected on what
would be defined as severe cases today by the grading system as defined by Lund (2003), probably
grade three to four lesions. The specificity was, however, very high which means that sows are not
falsely remarked for shoulder lesions.
Importantly, this survey was conducted before 2003 where new guidelines were introduced by
central authorities (Det Veterinære Sundhedsråd, 2003) which lead to an increased awareness of the
problem and probably to a higher sensitivity of the mandatory meat-inspections.
Still, the presented examples in table 1 and table 2 clearly illustrate the fact that when evaluating
mandatory meat-inspection data, one has to be aware of the “abattoir effect” that reflects the
different sensitivities on the mandatory meat-inspection.
2.7 Shoulder lesion in extended meat-inspection surveys Since 2002, a number of extended meat-inspection surveys have been made at abattoirs in order to
estimate the extent of the problem of shoulder lesions of sows, prevalence studies more or less
published. Comparing the surveys is not straight forward because different criteria were used in the
surveys. The new grading system introduced by Lund (2003) has only been used in his own
prevalence study and furthermore this is also the latest survey performed in this field. In table 4
results from more recent extended meat inspections surveys are presented.
19
Table 4.* Studies on the prevalence of shoulder lesions by extended meat-inspection Survey Prevalence – total Prevalence of
ulcers With exposed bone
Sample size Published
Christensen, G. 2002
Survey performed in 2000 at abattoirs in Skærbæk, Silkeborg and Sæby
9,9 %
7,0 %
1328 sows
Published
Jensen, RM 2002.
Swine specialist-assignment. Data collected at Sæby-abattoir in 2002.
6,6 %
--
Unknown
Unpublished
Garlov, A.M 2002-20031.
Survey at Skærbæk-abattoir. Performed with 8 months interval.
5,7 – 8,7 %
2,1
2 x 3000 Sows and boars
Unpublished
Lund, M. 2003
Master Thesis 2003. Survey performed at Skærbæk in 2003.
12,4 %
Where;
Grade 1 = 6,6% Grade 2 = 2,8% Grade 3 = 2,1% Grade 4 = 0,8%
0,8 %
3200 sows
Published
*Modified from Lund (2003) 1) No adjustments made for the number of boars included in this prevalence. Prevalence recordings are also to some extend affected by seasonal variation. Mandatory meat
inspection data collected at the Skærbæk abattoir from 2001-2002 showed a seasonal variation
(Lund, 2003) where the largest variation recorded was of approximately 60% (4.7% second quarter
2001 compared to 7.9 % third quarter 2002). The effect was clear when comparing the mean
prevalence for 2001 and 2002 which was approximately equal.
20
3. An abattoir survey with emphasis on the relation between clinical signs and post-mortem registrations
_____________________________________________________ 3.2 Introduction
3.2.1 Background The degree and thereby severity of shoulder lesions can in some cases be difficult to determine by
clinical inspection and palpation ante-mortem (Jensen and Svendsen, 2006). In this context the
wound can be undermined and have a greater extent than the mere penetration of the skin shows.
Accurately grading by use of the scale described by Lund (2003) requires that the damaged tissue
layers including the wound bed are identified to establish correct grading. This can be complicated
because the lesions to some extent are contaminated and concealed by debris and crusting (Lund,
2003). Also, the lesions may reflect a mixture of different ulcer-stages due to the fact that they are
often untreated lesions, results of repeating trauma and regenerative processes.
To date, no studies have been made on the relation between ante-mortem clinical findings and
detailed post-mortem pato-anatomical grading. Christensen (2003) made a survey where clinical
examination of shoulder lesions ante-mortem was compared to the registrations on the mandatory
meat-inspection with respect to the prevalence of shoulder lesions. However, no solid knowledge
concerning simple clinical signs predicting the more severe lesions post-mortem (grade three and
four) was extracted.
3.2.2 Objectives of the present abattoir survey 1) To estimate clinical and pathological prevalence of shoulder lesions and to evaluate possible
association between subcutaneous layer of fat and shoulder lesion prevalence.
2) To construct a stochastic biological model for prediction of probabilities for pathological
shoulder lesions (notifiable) using a Bayesian network by including relevant risk factors and
evidence of clinical signs of sows examined both ante- and post-mortem.
3) To deduce from the model combinations of simple clinical signs as marker of pathological
shoulder lesions for veterinarians in an advisory situation.
4) To estimate sensitivity and specificity of the diagnosis “notifiable shoulder lesion” of sows by
the mandatory meat inspection according to the detailed post-mortem examination (Golden
Standard).
21
3.3 Material and methods
3.3.1 Study design Data was collected during a two week period in November 2006 at a Danish abattoir in Skærbæk,
Jutland. The target population was Danish culled sows sent to abattoirs. The study population was
culled sows to be slaughtered at the abattoir of Skærbæk during a two week period in November
2006. The study was performed as an observational cross-sectional study during the first week of
data collection, also called a prevalence study (Houe et al., 2004a).
The study design was changed during the second week of sampling where sows were sampled on a
stratified basis in order to obtain better representation of all clinical signs to be used in the study of
clinical examination as marker for pathological sholder lesions. The study unit of this abattoir
survey was sows, except for the study of clinical examination as marker for pathological sholder
lesions. Here, the study unit was sow-shoulders.
Ante-mortem examination was performed by the same method in both sampling settings. To assess
shoulder lesions, the skin over the tuber of the spine of scapula (referred as the tuber) was examined
visually and by palpation, which earlier studies had shown to be the predominant site of lesions
(Davies et al., 1996). Beforehand a number of clinical symptoms had been selected based on
experience from earlier studies (Davies et al., 1996; Christensen, 2003; Zurbrigg, 2006; Jensen and
Svendsen, 2006) and evidence based on expert opinion (Nielsen, 2006). These clinical symptoms
were placed into a schedule for use at the abattoir-registrations (see enclosure 1).
Each sow was registered by an individual number and a unique herd-number, date of registration
and a visual body score (score 1 to score 5) was assigned as described by (Eriksen, 1991).
Furthermore, each shoulder was evaluated for possible combinations of alterations in the area
overlying the tuber spina scapula (each type of alteration is shown in table 3.1).
22
Table 3.1 Names and levels of the variables used for ante-mortem examination. Abbreviations in brackets. Name of skin-variable Levels
Skin-covered shoulder (Normal) (yes/no)
Erythema (Eryth.) (yes/no)
Crust (yes/no)
Swelling (Swell.) (1=none, 2=soft and 3=firm)
Tissue-loss (T. loss) (yes/no)
Diameter of skin, when skin = crust/scar (D. skin) (measured by callipers in mm)
Diameter of swelling (D. swell.) (measured by callipers in mm)
Adherence to the tuber (Adhere.) (yes/no)
Scar (yes/no)
The following clinical signs were recorded:
Skin-covered shoulder when there was no sign of epithelial deficit or scarring. Erythema when there
was redness in the skin overlaying the tuber or peripheral to a crust/swelling. Crust when there was
a dried exudate overlying an epithelial deficit. Swelling when there was an elevation of the skin and
the texture was determined as soft when in the consistency of a “tainted orange” and firm when in
the consistency of a “fresh orange”. Adherence to the tuber (adherence to the tuber = yes) whenever
a scar/crust or swelling by palpation was adherent to the underlying bony foundations and thereby
unable to be moved in a horizontal plane by digital manipulation. Scar when the skin was intact and
scar tissue was apparent at the site.
The diameter of swelling and the diameter of crust/scar (the largest with) were measured with
callipers, using a hierarchy of swelling rather than crust/scar when both signs were apparent. All
information was gathered in an outline for use at the abattoir (see enclosure one).
Post-mortem examination;
The sows examined by ante-mortem were slaughtered in sequence and provided with unambiguous
marking through the abattoir so that when leaving the platform of the mandatory meat-inspection
they were all sent to the veterinary platform (in Danish: “efterkontrol”) for a post-mortem grading
and a subcutaneous fat measurement (referred to as “fat-layer”). The referred grading system is
presented in table 3.2. Sows with grading three and four were also evaluated by a veterinarian of the
mandatory meat-inspection since sows with these lesions are notifiable by current legislation
(Anonymous, 2005).
23
Table 3.2 Grading of shoulder lesion in the shoulder region of sows on post-mortem*
Grade Description
0 No lesions of the skin
1 The lesion is limited to the epidermis, with or without a moderat crust.
2 The lesion involves the dermis, with or without extensive crusting. There is little fibrosis and/or
granulation tissue.
3 The lesion penetrates to the subcutis. There is intense formation of granulation tissue
4 Ulcer penetrating to the bone or ulcer development with periosteal bony proliferation.
*By Lund (2003), modified from Jensen and Svendsen (2006).
Fat-layer was measured with callipers (in mm) at the level of the first thoracic processus spinosus as
a proxy measure of the amount of soft tissue overlaying the tuber in accordance with Davies et al.
(1997). The measure-point of subcutaneous fat-layer was considered a valid proxy measure by
expert opinion (Thorup, 2006) of the back fat-layer used by Davies et al. (1997) .
Finally, disease codes and slaughter weights of the registered sows was provided from a central
database at the abattoir by the end of a day, collected by use of a unique slaughter-number, assigned
to each sow when passing the weight station.
All information was gathered in an outline (see enclosure two) unambiguously identified by sow-id,
date and a supplier number. See enclosure three for photos of sows ante- and post-mortem in
comparison.
To verify the correctness of the post-mortem grading of shoulder lesions, 25 cut-off shoulder
lesions representing different grading (one to four) were collected during the study period and saved
for an “observer agreement test” with a trained veterinarian of the mandatory meat-inspection. See
enclosure four for pictures of the setting and the results for each observer.
3.3.2 Sampling methods The arrival stable at the Skærbæk-abattoir is divided into three sections, Section A containing 12
pens, section B containing 8 pens and section C containing 4 pens. Each pen was filled with 30
sows each. The pens were emptied and filled during a day of slaughtering overall depending on the
proportion of sows delivered to the abattoir and sows slaughtered per day. Each day, a number of
sows stayed for the night awaiting slaughtering on the following day.
In sampling for the prevalence study, the recordings were made from 5.20 in the morning to 14.15
in the afternoon. Upon arrival each morning, sows have randomly been sampled among sows
delivered to the abattoir the day before between different sections and pens by drawing a random
number (1-24) and selecting the pen matching the number. During the day, sows were randomly
24
sampled along with delivering to the abattoir; again by drawing a number and sampling the pen
matching this number. A batch of sows was chosen by including all sows in each sampled pen. In
an effort to sample by random, however, sampling has sometimes been made by convenience (non-
probability sampling) depending whether it was possible to examine a given pen in a given section
according to the work flow.
Sampling during the second week of the study of clinical examination as marker for pathological
shoulder lesions was based on four predetermined inclusion criteria of sows with shoulder lesions;
1) Sows with a crust in the area overlaying the tuber >30 mm in diameter.
2) Sows with a soft- or firm swelling in the area overlaying the tuber.
3) Sows with adherent crust/scar to the tuber.
4) Sows with lesion penetrating to exposed bone.
3.3.3 Sample size The sample size necessary in the prevalence study was calculated to 385 sows (Win Episcope 2.0).
The basis of the calculation was;
- an estimated prevalence of shoulder lesions (grade 1-4) = 10%
- size of study population = 5000, L2 (maximum allowable error) = 3%
- level of confidence = 95%.
3.3.4 Descriptive and statistical analysis Data from ante- and post-mortem examinations were updated in two different spreadsheets in
Excel® version 2003, each sow by left- and right shoulders. The two data-sets were merged by a
hierarchy of date of examination, sow-id and shoulder–side. Thereby, a final data-set was
completed, containing information on both ante- and post-mortem examination comparable by
shoulder sides per sow.
3.3.4.1 The prevalence study In the prevalence study only data gathered during the first week of sampling was entered and
analyzed with “sows” as the study unit where each sow was selected by worst case shoulder lesion
at post-mortem (one line of data per sow). This data-set contains 363 sows and 19 variables (se
enclosure five for a print preview of data-set). All analysis performed was carried out in SAS®
version 9.1.
25
Descriptive analysis was made by calculating frequency distributions for the categorical variables
by the freq-procedure. The continuous variables were analyzed for location and spread by the
univariate-procedure.
Fat-layer (continuous variable in mm) was analyzed by a one-way analysis of variance with grading
as a class-variable. Also, the continuous variable fat-layer was divided into intervals (five levels)
and presented according to post mortem grading.
See enclosure 6 for a preview of all SAS-coding.
3.3.4.2 The study of clinical signs as marker for pathological sholder lesions (Bayesian net) In the study of clinical examination as marker for pathological shoulder lesions, consecutive data
from both weeks of sampling were combined and analyzed by the study unit “sow-shoulders”. This
procedure was established due to the correlation between clinical findings by ante-mortem
examination and post-mortem pathological findings of shoulder lesions were of interest. In this
context sow-shoulders was assumed independent.
The data-set for analysis contains 775 observations (sow-shoulders) and 20 variables (see enclosure
five for print preview). The variable “skin” with three levels; normal, crust and scar was created by
joining the latter variables under one variable (se table 3.1). Body condition score was dichotomized
into the variable “body condition” (denounced “Body cond.” in the Bayesian network) with two
levels (thin and normal/fat), where body condition score one and two = thin and body condition
score three, four and five = normal/fat.
In an effort to use clinical signs as predictor of pathological shoulder lesion, the vast information
collected is modelled in a Bayesian network. This is a probability model for a directed graph
showing the causality structure in the model (Jensen, 1996). The probabilities connected to the
arrows are conditional probabilities that show how the state of a variable influences the probability
distribution for the states of other variables (Otto and Kristensen, 2004). Evidence about the state
of a given variable brings light also to the states of the variables that cause this given variable (Otto
and Kristensen, 2004).
Input to the model is the state of the risk factor recorded in this study, body condition, and the
results of clinical examinations on shoulder lesions given the post mortem grading. The output of
the model is the probability distributions for the different degrees of pathological shoulder lesions.
The variable notifiable (yes/no) is the sum of the conditioned probabilities of degree three and four
shoulder lesions (from the parent node degree).
26
The variables in the model can only attain one of a finite number of states or levels (yes/no, 0-4,
thin/normal to fat etc.). When using the net, the distribution of all unknown variables depends on
the states of the known variables. Thereby, the probability distribution for a variable is a conditional
probability given the known states of this or other variables (Otto and Kristensen, 2004).
When a sow is presented with a shoulder lesion, a veterinary examination can be made by visual
inspection and palpation whereby information is gathered. The results of these “tests” will never tell
the true status of the shoulder lesion related to post-mortem grading but the results change the
probability distribution of the grading on post-mortem (i.e. our view on the severity of the shoulder
lesion and the stage of notification).
The causal structure of the network is shown in figure 3.1 and for a description of the clinical
variables the reader is referred to table 3.1 and for a description of the pathological grading the
reader is referred to table 3.2.
Figure 3.1 Initial causal structure of the Bayesian network modelling all the collected clinical signs according to the degree of pathological shoulder lesion by post-mortem examination with body condition as a risk factor.
The node tissue-loss was problematic. For all degrees of shoulder lesions, observations on tissue-
loss except for grade 3 were established. Therefore, on the assumption that tissue loss would
become more likely according to increasing grade of shoulder lesion, a logistic regression has been
performed with the following model entered in the genmod procedure (SAS 9.1).
27
Model
Logit (Pijk)) = α + βi + γ*xij, Pijk is the probability of tissue loss for the k’th shoulder of the i’th skin and with the j’th grading. α = intercept. βi = the effect of the qualitative variable skin, (i=1,2) xij = the continuous variable grading, (j= 1,…,4) with γ= the slope for the continuous variable.
For a print preview of output from the model the reader is referred to enclosure seven. The effect of
grading is not significant (p=0.17) as apposed to the effect of skin (p<0.001). Therefore, the arrow
connecting grading to tissue loss had to be dropped. Furthermore, the arrow from skin to tissue loss
had to be dropped as well because the nodes grading→ skin→ tissue loss are in a serial connection
and with the variable skin always observed on ante-mortem examination, tissue loss becomes d-
separated from grading as stated by Jensen (1996) for serial connections. One these grounds, the net
had to be revised. The revised net is shown in figure 3.2.
Figure 3.2 Revised causal structure of the Bayesian network modelling all the collected clinical signs according to the degree of pathological shoulder lesion by post-mortem with body condition as a risk factor
The node body condition has no parent node, and therefore the table reduces to unconditioned
probabilities and must have probabilities specified a priori as described by Jensen (1996). In this
case a probability distribution for body condition was calculated based on data from the prevalence
study.
The conditioned probabilities for the variable grading was calculated by the levels of the risk factor
body condition based on data from the prevalence study with the study unit “sow-shoulders”.
28
The conditional probabilities for the clinical variables adherence to tuber, erythema, skin and
swelling are calculated by each level of grading where data from both weeks of sampling entered as
mentioned before, again with the study unit sow-shoulders.
The variable skin models the node diameter of skin, if there is crust or scar (levels of the variable
skin) then there is a measurement to match. The same principle applies to swelling, i.e. if there is a
soft or firm swelling then there is a measurement of the diameter to match.
However, there is also an arrow (i.e. causal relation) from swelling to diameter of skin which needs
explanation. The reason is, as mentioned before, that a hierarchy of swelling rather than crust/scar
in measurement of diameter existed when both clinical signs were apparent. This hierarchy was
established on practical grounds to reduce the number of recordings on each sow. Thereby, if a
swelling is evident the diameter of the crust/scar is not a number in the network calculations.
The diameter of swelling and the diameter of skin (crust/scar) are continuous variables. For use in
the network a normal distribution was calculated for all diameters of crust/scar by grading when this
was apparent without swelling. This distribution was “chopped up” into parts of equally distance
(5mm) to represent different levels in the node diameter of skin.
For the variable diameter of swelling (with levels soft and firm) the same procedure was attempted.
However, no normal distribution could be estimated for the combination; soft swelling and grade
three shoulder lesion. On these grounds, the diameter of swelling was modelled by grading and
swelling as explanatory variables in two way analysis of variance as shown below.
Model:
ijkjiijkD εβαµ +++=
Dijk is the k’th diameter of the i’th swelling with the j’th post-mortem grading, αi= Swelling (soft/firm), (j = 2,3) βj= Post mortem grading, (i =0,..,4) εijk= Residual variation for i’th swelling with j’th grading and k repetitions, (k = 1,…,nij)
The model is run in the GLM procedure (SAS). All output from the model can be seen in enclosure
eight. This modelled distribution was “chopped up” into parts of equally distance (5mm) to
represent different levels in the node diameter of swelling.
29
The actual calculations of probabilities are made in the Bayesian network presented in figure 3.2
modelled in Esthauge® with kind permission and great effort by Ringaard Kristensen (2006).
3.3.4.3 Evaluation of inter-observer agreement. The inter-observer agreement of post mortem assessment of shoulder lesions is calculated as partial
agreement with a weighted kappa test due to the fact that test-results are scored on an ordinal scale
as described by Dohoo et al. (2003).
3.3.4.4 Sensitivity and specificity of the diagnosis “notifiable shoulder lesions”. For the final task of estimating sensitivity and specificity of the diagnosis “notifiable shoulder
lesion” by the mandatory meat inspection according to detailed post-mortem examination (Golden
Standard), the identification of sows recorded as “suspect of notifiable shoulder lesions” by the
mandatory meat-inspection is based on all sows examined during the two weeks of sampling with
the specific recording; disease-code 44 and “red code” (veterinary inspection demanded). This is
the chosen method of the mandatory meat-inspection when sows are suspect of a notifiable shoulder
lesion at the Skærbæk abattoir (Christensen, 2006).
3.4 Results
3.4.1 The prevalence study Sows from the prevalence study selected by worst case shoulder lesion grading and matching
combinations of clinical signs are presented in table 3.3 with combinations that occurred in >1% of
the cases.
30
Table 3.3 Combinations of clinical findings recorded by ante-mortem examination in the prevalence-study. Below, combinations with more than 1% prevalence are shown below by frequency in descending order. Combination Skin-
covered shoulder (yes/no)
Erythema (yes/no)
Crust (yes/no)
Tissue- loss (yes/no)
Swelling - (none) - (soft) - (firm)
Adherent (yes/no)
Scar (yes/no)
Number of sows (%)
1 Yes No No No None No No 273 (75.2%)
2 Yes No No No None No Yes 17 (4.6%)
3 No No Yes No None No No 13 (3.6%)
4 Yes No No Yes None No Yes 11 (3.0 %)
5 No No Yes No Firm No No 6 (1.7%)
6 Yes No No No Firm No No 5 (1.4%)
7 No Yes Yes No Soft No No 4 (1.1%)
8 No No Yes Yes None No No 4 (1.1%)
9 No No Yes No Firm Yes No 4 (1.1%)
Balance Sum
- -
- -
- -
- -
- -
- -
- -
26 (7.2%) 363 sows (100%)
From table 3.3 the presumable skin combination of normal sows without any lesion in the region
overlaying the tuber can be seen as combination one which is recorded in 75.2% of the cases. The
prevalence of sows with healed shoulder lesions (scar + scar and tissue loss) delivered to the
abattoir is 7.6%. Sows with skin lesion (crust) is found in 8.6% of the cases and sows with
underlying tissue reaction (firm or soft swelling) is recorded in 5.3% of the cases. Sows with both
skin-lesion and underlying tissue reaction are found in 3.9% of the sows. The specific combinations
of clinical findings of the notifiable shoulder lesion cases are presented in table 3.4 according to
grade of shoulder lesion at post-mortem. Table 3.4 Clinical findings of the notifiable shoulder lesion cases recorded by ante-mortem examination in the prevalence-study Comb. Skin-covered
shoulder (yes/no)
Erythema (yes/no)
Crust (yes/no)
Tissue- loss (yes/no)
Swelling - (none) - (soft) - (firm)
Adherent (yes/no)
Scar (yes/no)
Number of sows (%)
Grade
1 No No No No Firm Yes Yes 1 3
2 No Yes Yes No Firm No No 2 3
3 No No Yes No Firm Yes No 1 3
4 No Yes Yes No Firm Yes No 1 4
5 No No Yes No Firm Yes No 2 4
31
By studying the skin alterations recorded for the notifiable shoulder lesion cases, clinical findings
in common for the different cases can be deduced, also in comparison with lower grade shoulder
lesions (grade one and two) (see figure 3.3).
A) All notifiable lesions (n= 7 sows) with grade three and four
shoulder lesions.
B) Collected number of sows with lower grade shoulder lesions (grade one and
two, n=76). Out of the total of sows recorded without clinical findings but with a
pathological lesion, nine of the cases were grade two and 30 cases grade one.
Figure 3.3 A) Clinical findings of the notifiable shoulder lesion cases in the prevalence study and B) lower grade
shoulder lesions (grade one and two).
Not presented in figure 3.3, the eight lower grade shoulder lesion cases recorded with a firm
swelling are all measured with a width below 40 mm, whereas all the notifiable shoulder lesion
cases (figure 3.3 to the left) were measured with a width above 55 mm.
The prevalence of shoulder lesion recorded by post-mortem examination was calculated by worst
case shoulder lesion recorded per sow. 83 sows were recorded with shoulder lesions and 95
shoulder lesions were recorded in total. Table 3.5 shows the prevalence of shoulder lesions by post-
mortem investigation, worst case per sow.
The overall prevalence of shoulder lesions is stated to be 22.9% with a wide confidence interval
[18.7; 27.1%] (Win Episcope 2.0) due to the small sample size.
Skin-alteration (eryth./crust/scar)
Adherence (by palp.)
Swelling (firm)
6 1
Skin-alteration (eryth./crust/scar)
Adherence (by palp.)
Swelling (firm)
3
7
26
1
No findings 39
32
Table 3.5 Prevalence of post-mortem shoulder lesion-grading calculated as worst case recorded by each sow. Grad Number of sows Prevalence
0 280 77.13
1 45 12.40
2 31 8.54
3 4 1.10
4 3 0.83
Total 363 100
Only twelve sows were found with shoulder lesions on both shoulders. Of these, two sows have a
notifiable lesion on one side (grade three) and a lesion of a lower grading on the opposite shoulder
side (grade two and one respectively). In table 3.6 the distribution of the 95 recorded shoulder
lesions is presented by left- and right side distribution. Table 3.6 The distribution of shoulder lesions, left- and right shoulders of the sows, respectively. Grade 1 Grade 2 Grade 3 Grade 4 Total
Left side 26 15 2 2 45
Right side 25 22 2 1 50
Total 51 37 4 3 95
There was no clear pattern in comparison of parameter-estimates of fat-layer according to grading -
the expectation being that the estimate of fat-layer would decrease according to increasing grade of
shoulder lesion (see enclosure 9). In figure 3.4 a histogram of post-mortem shoulder lesion grading
is presented by intervals of fat-layer.
56
13
31
0 0
71
19
10
0 0
73
15
10
1 1
90
63
0 1
94
0 0
6
00
10
20
30
40
50
60
70
80
90
100
Grade 0 Grade 1 Grade 2 Grade 3 Grade 4
Post-mortem grading
Prev
alen
ce
Fat-layer <10 mm(n=16)
Fat-layer 10-20 mm(n=31)
Fat-layer 20-30 mm(n=204)
Fat-layer 30-40 mm(n=96)
Fat-layer > 40 mm(n=16)
33
Figure 3.4 Presentation of post-mortem grading by intervals of fat-layer. The numbers above each column represent the percentage of animals in the specific fat-layer group that were recorded with the given grade of shoulder lesion. As mentioned before, there were only very few observations for the higher gradings and therefore it
is difficult to deduce solid evidence on the association between subcutaneous fat-layer and shoulder
lesions prevalence which overall leaves an inconclusive pattern in this survey of subcutaneous fat-
layer and prevalence of shoulder lesions.
3.4.2 The study of clinical signs as marker for pathological sholder lesions (Bayesian net) In the following, the results from the survey are presented as basis of each node in the Bayesian
network which also serves to validate the results presented from the Bayesian network later on.
Table 3.7 presents the prevalence of body condition from the prevalence study. Table 3.7 Probabilities of body condition thin and normal/fat as found in the prevalence study. Body condition Prevalence Sample size
Thin 10.2 % 39 sows
Normal/fat 89.8 % 326 sows
Total 100 % 363 sows
The conditioned probabilities for the variable grading given body condition are presented in table
3.8 based on data from the prevalence study with the study unit “sow-shoulders”. Table 3.8 Conditioned probabilities for all grades of pathological lesions given body condition. The calculations on grading by body condition are based on data from the prevalence study with study unit “sow-shoulders”. The number of observations to each combination in brackets. Grade Body condition = Thin (no. of samples) Body condition = Normal/fat (no. of samples)
0 77.5% (58) 86.7% (532)
1 8.4% (6) 7.1% (43)
2 9.9% (7) 5.3% (33)
3 2.8% (2) 0.5% (3)
4 1.4% (1) 0.5% (3)
The conditional probabilities for the clinical variables adherence to the tuber, erythema, skin and
swelling are presented by each level of grading based on data from both weeks of sampling. The
conditional probabilities are shown in table 3.9.
34
Table 3.9 Conditional probabilities for the variables adherence to the tuber, erythema, skin and swelling calculated by each level of grading and with the number of observations to each combination (shown in brackets). Grade = 0 Grade = 1 Grade = 2 Grade = 3 Grade = 4
Adherence
No
Yes
99.20 %(619)
0.80 (5)
96.93% (53)
3.64 %(2)
93.33 %(70)
6.67 %(5)
44.44% (4)
55.56 %(5)
0% (0)
100% (11)
Erythema
Yes
No
1.76% (11)
92.24% (613)
7.27% (4)
92.23% (51)
20% (15)
80% (60)
44.44% (4)
55.56% (5)
18.18% (2)
81.82% (9)
Skin
Normal
Crust
Scar
86.04% (536)
4.82% (30)
9.15% (57)
52.73% (29)
29.09% (16)
18.18% (10)
25.68% (19)
51.35% (38)
22.97% (17)
11.11% (1)
77.78% (7)
11.11% (1)
0% (0)
100% (11)
0% (0)
Swelling
None
Soft
Firm
95.99% (599)
1.6% (10)
2.4% (15)
78.18% (43)
3.64% (2)
18.18 (10)
68% (51)
14.67% (11)
17.33% (13)
0% (0)
11.11% (1)
88.89% (8)
0% (0)
0% (0)
100% (11)
A normal distribution for all diameters of skin (crust/scar) by grading when this was apparent without swelling is presented in table 3.10. Table 3.10 Normal distributions (µ, σ) for the diameter of skin with the number of observations used to calculate each distribution. Grade Skin=1 (crust) Skin=2 (scar)
0
1
2
[34.30; 11.61], n=20
[32.60; 14.31], n=10
[37.14; 9.72], n=22
[35.70; 10.42], n=57
[32.40; 6.88], n=10
[42.20; 14.04], n=15
Parameter estimates and relevant output from the analysis of variance on the diameter of swelling
with explanatory factors swelling (levels soft and firm) and grading (1-4) are presented in table 3.11 Table 3.11 Parameter and selected output from the analysis of variance modelling the diameter of swelling. Parameter Estimate Standard error
Intercept 69.73 5.39
Grade= 1 Grade= 2 Grade= 3 Grade= 4
-19.30 -33.83 -25.70 0
7.50 6.85 8.05 -
Swelling= 2 Swelling =3
6.13 0
4.69 -
P-value Grading Swelling
0.001 0.1951
35
Table 3.11 shows that grading has a significant effect in terms of explaining diameter of swelling
(p<0.001) which is not the case for swelling (p=0.1951). That swelling is not significant is of minor
importance because the network under construction is modelling grading in accordance with clinical
signs. Furthermore, the parameter estimates show that the diameter of swelling increases according
to grading.
The Bayesian network will demonstrate how ante-mortem clinical evidence on shoulder lesion can
establish confidence in post-mortem grading of shoulder lesions and thereby the question of
whether the lesion is notifiable. Also, the state of the risk factor will be included and for selected
groups of evidence, the resulting probabilities of post-mortem grading and notifiability will be
presented (see table 3.12). Table 3.12 Tabulation of the probabilities (in percent) of post-mortem grade three, four and notifiable shoulder lesions given information of ante-mortem clinical signs and the state of the risk factor body condition
Grading Notifiability Evidence
3 4 Yes No 0 No evidence
0,72
0,58
1,3
98,8
1 Crust (yes)
5,4
5,6
11
89
2 Erythema (yes)
8,8
2,9
11,7
88,3
3 Soft swelling
3,1
0
3,1
96,9
4 Firm swelling
11,5
10,3
21,8
78,2
5 Crust, erythema and firm swelling (not considering extend)
48,2
22,9
71,1
28,9
6 Crust, erythema and a small firm swelling (30-35 mm)
28,5
7,0
35,5
64,5
7 Crust, erythema and a large firm swelling (60-65 mm)
56,8
24,9
81,7
18,3
8 Healed lesion (scar) that is adherent by palpation
24,6
0,0
24,6
75,4
9 Crust and large firm swelling (60-65) with adherence by palpation
33,2
63,8
97,0
3,0
10 Body condtion - Thin - Normal
2,8 0,48
1,4 0,48
4,2 0,96
95,8 99,04
11 Thin sow with crust, a large firm swelling (60-65mm) and adherence by palpation
44,7
53,7
98,4
1,6
12 Normal/fat sow with crust, a large firm swelling (60-65 mm) and adherence by palpation
28,4
68,1
96,5
3,5
36
The first row in table 3.12 shows the probabilities (in percent) of post-mortem grade three, four and
notifiable shoulder lesions without any evidence. This is the conditioned probabilities calculated in
the net based on data of what one would expect to find if there is no evidence given, and we have to
rely on a priori information on body condition and the resulting conditional probabilities in the net.
Comparing evidence of the skin (erythema and crust) and evidence of underlying tissue reaction
(firm swelling), the probability of notifiability rises approximately by the double percentage (from
~11% to 21,8%). When evidence of both the skin and of underlying tissue reaction is present (crust,
erythema and firm swelling), the probability rises by the triple percentage (21,8% to 71,1%)
compared to evidence of underlying tissue reaction alone (firm swelling).
In table 3.12 the diameter of a firm swelling was entered with two different intervals while keeping
evidence of the skin unchanged (erythema and crust). The intervals as basis of comparison are
chosen as being one standard deviation to either side of the mean of the diameter of swelling (figure
3.3). The intervals are 30-35 mm (small lesion) and 60-65 mm (large lesion), respectively. The
probability of a shoulder lesion being notifiable rises by approximately 2.3 times (35.5% to 81.7%)
when increasing the width of the lesion from 30-35 mm to 60-65 mm.
Example nine, including adherence by palpation, results in a very high probability of the shoulder
lesion being notifiable (96.7%). Also, it is seen from the table that 2/3 of the total probability of
being notifiable is allocated to grade 4 shoulder lesions.
Finally, if known state of the risk factor body condition is used as the only evidence the risk of
notifiable shoulder lesion increases approximately 4,5 times (from 0.96% to 4.2%) – a fairly large
increase but from a low level. If known state of the body condition is added to the evidence of a
severe shoulder lesion (se table 3.12) the probability is increased by 1.04 times (from 96.5 to 98.4
%) for thin sows having a notifiable lesion by post-mortem examination compared to normal/fat
sows.
3.4.3 Evaluation of inter-observer agreement The weighted kappa-coefficient calculated from the observer agreement-test was 0.64 with a 95%
CI [0.42; 0.86]. This is interpreted as excellent agreement (in the interval 0.6-0.8) as described by
Fleiss (1981) cited from (Houe et al., 2004b).
37
3.4.4 Valuable clinical signs as marker of pathological shoulder lesions Based on calculations in the Bayesian network the most probable markers of notifiable shoulder
lesions are;
Firm swellings with a fair extent (>50 mm in width).
Adherence of lesions to the underlying bony foundation.
Crusting and erythema only when overlaying larger firm lesions.
Summarized;
- The condition of the skin (crust/scar)) in itself is of little value if not compared with the palpable
findings in the tissue underneath where especially adherence to the underlying bony foundation (the
tuber spina scapula) and firm larger swellings are the best marker of pathological lesions being
notifiable (grade 3 and 4).
3.4.5 Sensitivity and specificity of the diagnosis “notifiable shoulder lesion” Table 3.12 Cross tabulation of notifiable shoulder lesions estimated by detailed pato-anatomical examination (Golden Standard) in relation to the mandatory meat-inspection. Notifiable Not notifiable Sum
Code 44 and “red label” 16 10 26
No coding 4 382 386
Sum 20 392 412 sows
- Sensitivity = 80% [55.7; 93.4]*
- Specificity = 97% [95.2; 98.7]*
*The calculations have been performed on the VassarStats-homepage (VassarStats, 2006).
3.5 Discussion
3.5.1 The prevalence-study The sows delivered to the abattoir in question are collected from most parts of Jutland and the
abattoir in Skærbæk is slaughtering more than half of all Danish culled sows per year. In 2005 a
total of 233,547 sows were slaughtered at the abattoir in Skærbæk (Christensen, 2006) out of a total
of 433,000 slaughtered/exported sows on a national scale (Danmarks Statestik, 2006) which equals
a proportion of 54 %. Also, the sows in the prevalence study were sampled from 148 different
farmers where the maximum delivered sows per farmer were 10 - only recorded for two different
suppliers. On these grounds, the sows in the study population are assumed representative of the total
population of culled sows from Danish sow farms related to the prevalence study.
38
The obtained sample size for the prevalence study is not as large as calculated. 363 sows were
examined in comparison with the 385 sows calculated as necessary sample size. This has an
implication for the accuracy with which the apparent prevalence can be estimated (the maximum
allowable error increases by 0,09%, i.e. from 3% til 3,09% under the same assumptions).
It has been shown that the lower grade shoulder lesion cases are more difficult to detect at ante-
mortem examination since 39 cases were found only at post-mortem examination. Of these, nine
cases are grade two lesions. This is clearly a problematic finding, because it illustrates that shoulder
lesion diagnosis can be difficult at ante-mortem and that veterinarians are faced with a difficult task
at hand because they have also to mind other aspect at the same time. However, all notifiable cases
were detected at ante-mortem, and they were described by approximately the same clinical
symptoms (skin alteration and firm swelling that is adherent by palpation). Also, the width of the
firm swellings had a clear impact on the grading at post-mortem since the eight lower grade
shoulder lesion cases with firm swelling are all measured with a width below 40 mm, whereas all
the notifiable shoulder lesion cases (figure 3.3 to the left) were measured with a width of the firm
swellings above 55 mm. Thus, applying the width will differentiate the notifiable shoulder lesions
from lower grading shoulder lesion cases with respect to clinical signs.
The prevalence of post-mortem shoulder lesions is much higher (22.9%, grade 1-4 in total) than
what was reported by Lund (2003). In the present study grade one lesions are found with a
prevalence of 12.4% compared to 6.6% and grade two lesions are found with a prevalence of 8.5%
compared to only 2.8% in the study by Lund (2003). For the more severe gradings, the prevalences
are in accordance with findings reported by Lund (2003) having prevalences of 2.1% and 0.8% for
grade 3 and 4 shoulder lesions compared to 1.1% and 0.8% in the present study.
Reasons for bias on post-mortem grading may be that some level of overestimation of grade one
shoulder lesions was made due to the fact that grade one lesions limit to the epidermis, and they are
easily mistaken for traumatic lesions/bite wounds and may figure as false positives on these
grounds. Presumably, the prevalence of grade two lesions in this survey may have been
overestimated because they also include some grade three lesions that were not recorded as such
because of the high specificity applied to shoulder lesion diagnosis which may lower the sensitivity,
i.e it requires a very high level of certainty before cases are reported (Christensen, 2006). Again,
grading scales are open to bias and subjectivity due to individual interpretation which reflects user
39
knowledge and clinical ability to identify anatomical structures and relevant clinical changes – all
aspects which make grading scales vulnerable to low levels of inter-rater reliability (Pedley, 2004).
The prevalence-estimates from the present study is based on a sample size that equals only ~11% of
the samples included in the study by Lund (2003) which results in a higher level of uncertainty
connected to the estimates of prevalence in this present study. The wide confidence interval
calculated for the overall prevalence [18.7; 27.1%] reflects this lower power.
The fat-layer measured in this survey is used as an approximated back fat measure which has
proved to be a significant factor on the shoulder lesion prevalence in earlier studies (Davies et al.,
1997; Christensen et al., 2002). However, the results in this survey are inclusive due to the small
number of samples in the higher end of the shoulder lesion grading scale (grade 3 and 4) and
because the distribution of fat-layer measurements does not allow grouping into for example a thin
and thick fat-layer group.
3.5.2 The study of clinical signs as marker for pathological shoulder lesions (Bayesian net) In this data-set soft swellings are not very reliable markers of notifiable lesions (low probability)
which indicate that they may have been clinical recordings of abscesses or hematomas found by
post-mortem examination; therefore they cannot be deduced as reliable markers for pathological
shoulder lesions.
In table 3.12 cases of shoulder lesions were created based on selected evidence entered into the
Bayesian net. Specific combinations of clinical symptoms combined with knowledge of a poor body
condition resulted in a probability of 98 % for such a lesion being notifiable. However, caution is
demanded when directly trying to extrapolate these results to the target population being Danish
culled sows delivered to abattoirs. These conditioned probabilities calculated in the Bayesian net are
only as valid as the data foundation on which they are calculated (the number of animals to each
combination of symptom by grade). In this specific abattoir survey only 20 notifiable lesions and a
total of 151 shoulder lesions were evaluated.
A possible source of bias to this part of the survey is the sampling procedure during the second
week of sampling. 13 of the 20 notifiable shoulder lesions were sampled during this week of
sampling – all sampled on predefined criteria in order to achieve a better representation of all
clinical signs. In this context it is possible that the clinical signs being very good markers of
notifiable lesions to some extend are an outcome of the sampling procedure.
40
Still, this is the first survey conducted in this specific field of research with the relation between
clinical findings and post-mortem evaluation on shoulder lesions in sows. Therefore, the results
obtained are my proposal to a precise description concerning the relation. Also, animals were
examined and described by combinations of clinical signs as they were apparent. This vast
information (i.e. large number of combinations) was gathered in a Bayesian network and modelled
according to the post-mortem assessment for each symptom recorded. Therefore, the relation
between clinical findings and post-mortem assessment was subject to an optimum unbiased
evaluation, also because predetermined scales of clinical signs have not been applied to the sows as
in previous studies on ante-mortem examination.
3.5.3 Evaluation of inter-observer agreement The inter-observer agreement test supports a notion of a post-mortem grading done with a fair level
of correctness in the present study. The result shows a test performed in excellent agreement with a
trained veterinarian of the mandatory meat-inspection (kappa=0.64). Still, the latter is based on the
correct grading at post-mortem examination by the trained veterinarian.
3.5.4 Valuable clinical signs as marker of pathological shoulder lesions Some clinical findings are more valid than others as marker for notifiable shoulder lesions. On these
grounds, I have summarized some recommendations related to the clinical examination of shoulder
lesions. Importantly, it has been shown in the prevalence study that the notifiable shoulder lesions
are grouped almost with the same clinical findings and these findings also result in a very high
probability of the shoulder lesion cases being notifiable (~97%) in the Bayesian network. Also,
there is a clear effect of the diameter of lesions in both the prevalence study and in the Bayesian net.
All the lower grade shoulder lesion cases are considerably smaller in extent than the notifiable ones
which differentiates the notifiable shoulder lesions from lower grading shoulder lesion cases with
respect to clinical signs. Thereby, it is reasonably to deduce reliable markers from the Bayesian
network.
3.5.5 Sensitivity and specificity of the diagnosis “notifiable shoulder lesion” A fairly high sensitivity, 80 % with a confidence interval [55.7; 93.4] and a high specificity, 97%
with a confidence interval [95.2; 98.7] was found for the mandatory meat-inspection when
diagnosing notifiable shoulder lesions. This indicates that much higher proportion of severe
shoulder lesions are being found by the mandatory-inspection (i.e. higher sensitivity) than what has
been reported in an earlier study by Christensen (2003) who estimated a sensitivity of
41
approximately 54%. The specificity was high in this survey and also in the survey by Christensen
(2003). This implies that notifiable lesions are seldom falsely diagnosed as being notifiable (code
44 and read code) by the mandatory meat-inspection (few false-positive). The two studies are not
directly comparable because the Golden Standard by Christensen (2003) was defined as severe
lesions diagnosed by ante-mortem examination where the Golden Standard used in the present
study is grade three and four shoulder lesions by post-mortem examination. Still, the sensitivity is
higher today in 2006 than before the new recommendations from 2003 (Det Veterinære
Sundhedsråd, 2003). The estimates presented from this survey are to some extent biased because the
sampled sows pass the mandatory meat-inspection platform in sequence and it therefore is possible
that the veterinary technicians may have been somewhat “alerted”.
3.6 Conclusion The lower grade shoulder lesion cases (grade one and two) were more difficult to detect at ante-
mortem examination than post-mortem since 39 cases (30 grade one- and nine grade two lesions)
was found only at post-mortem examination. However, all notifiable cases were detected at ante-
mortem, and they were described by approximately the same clinical symptoms (skin alteration and
firm swelling (>55 mm) that is adherent by palpation). The collected prevalence of notifiable
shoulder lesions (grade three and four by post-mortem investigation) was in this survey 1.93%.
It was not possible to deduce an association between subcutaneous fat-layer and shoulder lesions
prevalence which leaves an inconclusive pattern in this survey of subcutaneous fat-layer and
prevalence of shoulder lesions.
A stochastic biological model for pathological shoulder lesions was constructed using a Bayesian
network approach where grading by post-mortem investigation was modelled by evidence of
clinical findings from ante-mortem investigation and knowledge of the only included risk factor,
body condition. The combination of a shoulder lesion case recorded with crust, a large firm
swelling (60-65mm) and adherence by palpation resulted in 97 % probability of the shoulder lesion
being notifiable on post mortem examination. These combinations were recorded in six out of seven
cases from the prevalence study.
Results from the model show that when undertaking clinical examination of shoulder lesions, the
condition of the skin (crust/scar)) in itself is of little value if not compared with the palpable
findings in the tissue underneath where especially adherence to underlying bony foundation (the
42
tuber) and firm larger swellings are the best marker of pathological lesions being notifiable (grade 3
and 4).
Most probable markers of notifiable shoulder lesions were;
Firm swellings with a fair extend (>50 mm in width)
Adherence of firm swellings of some extend
Crusting and erythema when overlaying larger firm lesions.
A fairly high sensitivity, 80 % with confidence interval [55.7; 93.4] and a high specificity, 97%
with confidence interval [95.2; 98.7] was found at the mandatory meat-inspection when diagnosing
notifiable shoulder lesions.
3.7 Perspectives Markers of pathological shoulder lesions were deduced in this abattoir-survey. The next step in
obtaining more solid knowledge on ante-mortem examination of shoulder lesions is to apply the
deduced markers in a new field trial where positive predictive values can be calculated on basis of
how the test performs according to post-mortem grading. Thereby, a measure of the validity of the
markers can be obtained for use in advisory situations of farmers when they in the future are
making an intervention (culling, treating sows in sick-pens, slaugther). The positive predictive
values should be applied to evaluate how these markers perform because they are prevalence-
dependent.
Pressure and duration experiments in the shoulder region of sows should be conducted in the
nearest future. This should elucidate whether pressure ulcers can develop “from bottom-to-top” or
not. This will influence what is interpreted as “in time interventions”. If erythema in skin is the only
evident sign in the skin of a sow already affected by a large underlying necrosis then isolation in
sick-pens with soft flooring will not prevent ulcer development. In this case new criteria for
intervention should be established in order to prevent these lesions.
43
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Dohoo, I., Martin, W., Stryhn, H., 2003. Veterinary Epidemiologic Research. University of Prince Edward Island, 550 University Avenue Charlottetown, Prince Edward Island; Prince Edward Island.
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pp. 91 -92
Edlich, R.F., Winters, K.L., Woodard, C.R., Buschbacher, R.M., Long, W.B., Gebhart, J.H., Ma, E.K., 2004. Pressure ulcer prevention. J. Long. Term. Eff. Med. Implants. 14. pp. 285-304
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König, H.E., Liebich, H.G., Bragulla, H., 2005. Veterinary anatomy of domestic mammals. textbook and colour atlas. Schattauer, Stuttgart. pp. 186 -188
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48
5. Enclosures
Enclosure 1
Schedule for ante-mortem examination
Enclosure 2
Schedule for post-mortem examination
Enclosure 3
Photos of sows ante- and post-mortem for comparison
Enclosure 4
Kappa-test with setting and results
Enclosure 5
Print of data-set for the prevalence study and the data-set for the study
of clinical signs as predictor of notifiable shoulder lesions.
Enclosure 6
Print of all SAS-coding used in data-analysis
Enclosure 7
Output for the logistic analysis of tissue loss
Enclosure 8
Output for the model of diameter of swelling
Enclosure 9
Output for the one-way analysis of variance of fat-layer by grading
49
Enclosure 1 ________________________________________________________________________________
Enclosure 2
1
Enclosure 3
Sow number 257 - Nov. 15th 2006
Post-mortem; Grade 3 Ante-mortem; Crust, erythema, firm swelling
diameter of swelling = 71 mm
Sow number 356 – Nov. 16th 2006
Post-mortem; Grade 4 Ante-mortem; Crust, tissue-loss, adherent, firm swelling = 58 mm
2
Sow number 2137 – Nov. 8th 2006.
Post-mortem; Grade 4 Ante-mortem; Crust, erythema, firm adherent swelling =
72 mm
Sow number 369 – Nov. 8th 2006.
Post-mortem; Grade 2 Ante-mortem; Crust and firm swelling = 35mm
3
Enclosure 4
The FREQ Procedure Table of (obs_he by obs_js) obs_he(obs_he) obs_js Frequency‚ Percent ‚ 1‚ 2‚ 3‚ 4‚ Total ƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆ 1 ‚ 1 ‚ 4 ‚ 0 ‚ 0 ‚ 5 ‚ 4.00 ‚ 16.00 ‚ 0.00 ‚ 0.00 ‚ 20.00 ƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆ 2 ‚ 3 ‚ 8 ‚ 0 ‚ 0 ‚ 11 ‚ 12.00 ‚ 32.00 ‚ 0.00 ‚ 0.00 ‚ 44.00 ƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆ 3 ‚ 0 ‚ 2 ‚ 3 ‚ 0 ‚ 5 ‚ 0.00 ‚ 8.00 ‚ 12.00 ‚ 0.00 ‚ 20.00 ƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆ 4 ‚ 0 ‚ 0 ‚ 0 ‚ 4 ‚ 4 ‚ 0.00 ‚ 0.00 ‚ 0.00 ‚ 16.00 ‚ 16.00 ƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒˆ Total 4 14 3 4 25 16.00 56.00 12.00 16.00 100.00
Weighted Kappa Coefficien
ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ Weighted Kappa 0.6411 ASE 0.1118 95% Lower Conf Limit 0.4219 95% Upper Conf Limit 0.8604 Sample Size = 25
4
Enclosure 5
Prevalens-study – print preview
f o s s s p r l l l l h h s h s h s g g g a u u a a k u l t t t c l d r a o v e y l l g _ _ _ s e d _ o r m v v d e d t k k k o d r _ d e s f s e e v _ g _ o o o O _ a i l a d k a t l l _ d r v d d d b i t n e e m r n a s i a n o a g e e e s d o g v k e p g b e g r r d d t 1 2 3 1 14 09NOV2006 hs 3 1 2 2 0 2 1 1 2 . 24 0 . . . . 2 17 08NOV2006 hs 3 1 2 2 0 2 1 1 2 21601 24 2 153.2 23 41 1 3 20 07NOV2006 hs 3 1 2 2 0 2 1 1 2 3282 23 0 217.7 1 1 1 4 36 09NOV2006 hs 3 2 2 1 36 1 1 1 2 69977 24 1 154.9 1 1 1 5 38 08NOV2006 hs 2 1 1 2 30 2 1 1 2 71283 27 0 148.4 1 1 1 6 41 06NOV2006 vs 3 1 2 2 0 2 1 1 2 23050 34 1 167.0 23 1 1 7 42 08NOV2006 hs 4 1 2 2 34 2 1 1 1 69977 41 0 199.3 1 1 1 8 45 07NOV2006 hs 3 1 2 2 0 2 1 1 2 63765 21 0 137.7 1 1 1 9 50 08NOV2006 hs 4 1 2 2 0 2 1 1 2 69977 34 0 168.3 66 1 1 10 65 06NOV2006 hs 3 1 2 2 0 2 1 1 2 29962 32 0 218.2 71 1 1
Study of clinical signs as marker for pathological lesions f o s s s p r l l l l h h s h s h s g g g a u u a a k u l t t t c l d r a o v e y l l g _ _ _ s e d _ o r m v v d e d t k k k o d r _ d e s f s e e v _ g _ o o o O _ a i l a d k a t l l _ d r v d d d h b i t n e e m r n a s i a n o a g e e e u s d o g v k e p g b e g r r d d t 1 2 3 d 761 679 17NOV2006 vs 2 2 2 1 56 2 3 1 2 . 16 0 . 44 1 1 1 762 773 17NOV2006 hs 3 2 2 1 53 1 1 1 2 12968 30 2 . 71 1 1 1 763 773 17NOV2006 vs 3 1 2 2 46 1 1 1 1 12968 30 1 . 71 1 1 2 764 966 17NOV2006 hs 3 1 2 2 0 2 1 1 2 78376 31 0 . 1 1 1 0 765 966 17NOV2006 vs 3 2 2 1 53 1 1 1 2 78376 31 2 . 1 1 1 1 766 1051 17NOV2006 hs 2 2 2 1 84 2 3 2 2 55778 16 4 . 44 1 1 1 767 1051 17NOV2006 vs 2 1 2 2 34 1 1 1 1 55778 16 2 . 44 1 1 2 768 1116 17NOV2006 hs 2 2 2 1 70 2 3 2 2 23207 14 4 . 44 1 1 1 769 1116 17NOV2006 vs 2 1 2 2 0 2 1 1 2 23207 14 0 . 44 1 1 0 770 1122 17NOV2006 hs 2 2 2 1 61 2 3 1 2 5688 22 2 . 71 1 1 1 771 1122 17NOV2006 vs 2 2 2 1 33 2 1 1 2 5688 22 0 . 71 1 1 1 772 1200 17NOV2006 hs 3 2 2 1 57 1 3 2 2 . 24 4 . 44 1 1 1 773 1200 17NOV2006 vs 3 1 2 2 0 2 1 1 2 . 24 0 . 44 1 1 0 774 2178 17NOV2006 hs 3 1 2 2 50 1 1 1 1 . 19 2 . 44 1 1 2 775 2178 17NOV2006 vs 3 2 2 1 48 1 3 1 2 . 19 0 . 44 1 1
5
Enclosure 6 Prevalens –study libname dat "D:\Speciale_skuldersår\Data"; data a; set dat.tvaersnit; if so_id=1358 and dato=mdy(11,07,06) then so_id=1359; where grad<5; run; *Der udvælges én linje data per so baseret på værste grad; proc sort data=a; by grad; run; proc sort data=a out=b; by so_id dato descending grad; run; proc print data=b; where grad>4; ; run; data c; set b; by so_id dato descending grad; if first.so_id; run; *Kliniske symptomer gruppering; data xy; set c; if hud_daek = 1 then hud = 0; if saarskrp = 1 then hud = 1; if afhelet_laes = 1 then hud = 2; if roedme=1 then hud=3; if hud=. then hud=0; if haevelse=. then haevelse=1; if forskydelig=. then forskydelig=1; where 0< grad <3; run; data hud_comp; set xy; if hud>0 and forskydelig=1 and haevelse=1 then hud_comp=1; if haevelse>2 and forskydelig=1 and haevelse=1 then hud_comp=2; if forskydelig=2 and hud=0 and haevelse=1 then hud_comp=3; if hud>0 and haevelse>2 and forskydelig=1 then hud_comp=4; if haevelse>2 and forskydelig=2 and hud=0 then hud_comp=5; if hud>0 and forskydelig=2 and haevelse=1 then hud_comp=6; if hud>0 and forskydelig=2 and haevelse>2 then hud_comp=7; run; proc freq data= hud_comp; tables Hud_comp; run; proc print data=hud_comp; run; data hud_comp1; set hud_comp; if hud=0 and forskydelig=1 and haevelse=1 and grad=2 then hud_comp=10; run; proc freq data= hud_comp1; tables hud_comp; run; Data hud_comp2; set hud_comp;
6
if hud >0 and haevelse>2 and omfang >40 then hud_comp=11; run; proc freq data= hud_comp2; tables hud_comp; run; *Skuldersår fordelt på huld-gruppering; proc sort data=c; by grad; run; proc gplot data=c; plot grad*huld_dod; symbol V=dot I=RL C=BLUE; run; proc mixed data=c; class grad; model huld_dod = grad / solution outp=stat; lsmeans grad/ pdiff; run; proc univariate data=stat; var resid; histogram resid / normal; qqplot resid /normal (MU=EST SIGMA=EST); proc gplot data=stat; plot resid*pred /vref=0; run; data c1; set c; nygrad=SUM(grad,1); loggrad=log10(nygrad); run; proc mixed data=c1; model loggrad = huld_dod / solution outp=stat; run; proc univariate data=stat; var resid; histogram resid / normal; qqplot resid /normal (MU=EST SIGMA=EST); run; proc reg data=c1; model loggrad= huld_dod; run; data c13; set c; if huld_dod=<10 then huld_dod_gr=1; if 10< huld_dod =<20 then huld_dod_gr=2; if 20< huld_dod =<30 then huld_dod_gr=3; if 30 < huld_dod =< 40 then huld_dod_gr=4; if huld_dod > 40 then huld_dod_gr=5; run; proc freq data= c13; tables huld_dod_gr*grad; run; *Højre og venstre skuldersår, test for forskel; proc sort data=a; by so_id; run;
7
data c14; set a; by so_id; if first.so_id; keep so_id; run; data c14a; set a; if placering = "hs" then grad_hs=grad; if grad_hs = . then delete; keep so_id grad_hs; data c14b; set a; if placering = "vs" then grad_vs=grad; if grad_vs = . then delete; keep so_id grad_vs; run; data c14ab; merge c14 c14b c14a; by so_id; if grad_hs=. then grad_hs=0; if grad_vs=. then grad_vs=0; run; proc freq data=c14ab; tables grad_hs*grad_vs / exact ; run; *Isolering af søer med dobbelte skuldersår i datasættet d; data x; set c14ab; if grad_hs > 0 and grad_vs > 0; proc print data=x ; var so_id grad_hs grad_vs; run; *Symptom fordeling ved kombinationens hyppigheder; proc freq data=c; tables hud_daek*roedme*saarskrp*vvstab*forskydelig*afhelet_laes*haevelse/ noprint out=c2; run; proc print data=c2; run; *Tabulering af kombinationer med >=4 søer; data c3; set c2; where count>=4; run; proc print data=c3; run; *Generering af ny variable - Hævelse_omfang; data cp; set c; if haevelse > 1; run; goptions reset=all; ods rtf style=journal; ods graphics on; Proc univariate data=cp; var omfang; histogram omfang / normal; qqplot omfang /normal (MU=EST SIGMA=EST);
8
run; ods rtf close; run; *generering af ny variabel - saar_omfang. Bemærk at det kun er skuldre UDEN hævelser, der medtages her, idet søer med hævelser indgår i variablen Haevelse_diameter; proc sort data = c; by grad haevelse; data cpp; set c; if haevelse = 1; if hud > 0; run; proc sort; by hud; proc univariate data=cpp; class hud; var omfang; run; *evaluering af parameteren slagtevægt - fortsat datasæt c; Proc univariate data=c; var slgt_vgt; histogram slgt_vgt / normal; qqplot slgt_vgt / normal (MU=EST SIGMA=EST); Run; *evaluering af slagtevægt og skuldersår - vægtgrupper baseres på median i datasæt e; data e; set c; if slgt_vgt < 185 then slgt_vgt_gr='smal'; if slgt_vgt > 185 then slgt_vgt_gr='large'; if slgt_vgt =. then delete; run; *Antal lev_nr i tværsnitsundersøgelsen (datasæt f); data f; set c; run; proc sort data=f; by lev_nr; run; proc freq data=f; tables lev_nr / out=f1; run; proc print data=f1; run; proc freq data=f; tables lev_nr; where lev_nr=.; run; *Antal søer per lev_nr; proc means data=f nway noprint; class lev_nr; var so_id; output out=N_lev (drop=_:) n=antal_so; run; proc means data=N_lev nway noprint; class antal_so;
9
var lev_nr; output out=N_so_lev (drop=_:) n=N_lev; run; proc print; run; data tabul; merge e N_lev (in=i where=(antal_so>5)); by lev_nr; if i; run; proc print data=tabul; run; Study of clinical signs as marker for pathological lesions libname js "D:\Speciale_skuldersår\Data"; *dannelse af variablen hud og udvælgelse af skuldersår grad 0-4; data et; set js.tvaersnit js.case; if hud_daek = 1 then hud = 0; if saarskrp = 1 then hud = 1; if afhelet_laes = 1 then hud = 2; if grad < 5; run; *strattificering af roedme på grader; proc sort; by grad; proc freq; by grad; tables roedme; run; *strattificering af forskydelighed på grader; proc freq; by grad; tables forskydelig; run; *strattificering af haevelse på grader; proc freq; by grad; tables haevelse; run; *strattificering af hud på grader; proc freq; by grad; tables hud; run; *Generering af ny variable - Hævelse_omfang; proc sort data = et; by grad haevelse; data to; set et; if haevelse > 1; run; proc means data=to; by grad haevelse; var omfang; run; proc glm data=to;
10
class grad haevelse; model omfang = grad haevelse/solution ss3; lsmeans grad haevelse; run;quit; *generering af ny variabel - saar_omfang. Bemærk at det kun er skuldre UDEN hævelser, der medtages her, idet søer med hævelser indgår i variablen Haevelse_diameter; data tre; set et; if haevelse = 1; if hud > 0; proc sort; by grad hud; proc means; by grad hud; var omfang; run; *Dannelse af knuden Body condition og beregning af gradsfordeling efter BC; data etb; set js.tvaersnit; if huld_lev<3 then huld='tynd'; if huld_lev =>3 then huld='normal/tyk'; where grad<5; run; proc freq data=etb; tables huld; run; proc sort data=etb; by huld grad; run; proc freq data=etb; tables grad; by huld; run; *Dannelse af datasættet fire udfra datasæt et og dannelse af knuden vævsstab; data fire; set et; where hud>0; run; proc sort data=fire; by grad hud; run; proc freq data=fire; tables vvstab / norow nocol; by grad hud; run; Proc contents data=fire; run; proc genmod data=fire; class hud; model vvstab = grad hud / type3 link=logit dist=bin; run;
11
Enclosure 7
___________________________________________________________________ The GENMOD Procedure
Model Information Data Set WORK.FIRE Distribution Binomial Link Function Logit Dependent Variable vvstab vvstab Number of Observations Read 187 Number of Observations Used 187 Number of Events 67 Number of Trials 187 Class Level Information Class Levels Values hud 2 1 2 Response Profile Ordered Total Value vvstab Frequency 1 1 67 2 2 120 PROC GENMOD is modeling the probability that vvstab='1'. One way to change this to model the probability that vvstab='2' is to specify the DESCENDING option in the PROC statement. Criteria For Assessing Goodness Of Fit Criterion DF Value Value/DF Deviance 184 229.5540 1.2476 Scaled Deviance 184 229.5540 1.2476 Pearson Chi-Square 184 186.7962 1.0152 Scaled Pearson X2 184 186.7962 1.0152 Log Likelihood -114.7770 Algorithm converged
The GENMOD Procedure Analysis Of Parameter Estimates Standard Wald 95% Confidence Chi- Parameter DF Estimate Error Limits Square Pr > ChiSq Intercept 1 -0.1347 0.2322 -0.5899 0.3205 0.34 0.5620 grad 1 0.2015 0.1475 -0.0876 0.4906 1.87 0.1720 hud 1 1 -1.3170 0.3606 -2.0237 -0.6102 13.34 0.0003 hud 2 0 0.0000 0.0000 0.0000 0.0000 . . Scale 0 1.0000 0.0000 1.0000 1.0000 NOTE: The scale parameter was held fixed. LR Statistics For Type 3 Analysis Chi- Source DF Square Pr > ChiSq grad 1 1.87 0.1710 hud 1 14.38 0.0001
12
Enclosure 8
The GLM Procedure Class Level Information Class Levels Values grad 5 0 1 2 3 4 haevelse 2 2 3 Number of Observations Read 81 Number of Observations Used 81
Dependent Variable: omfang omfang Sum of Source DF Squares Mean Square F Value Pr > F Model 5 8730.87793 1746.17559 5.47 0.0002 Error 75 23939.14677 319.18862 Corrected Total 80 32670.02469 R-Square Coeff Var Root MSE omfang Mean 0.267244 34.17888 17.86585 52.27160 Source DF Type III SS Mean Square F Value Pr > F grad 4 8714.794024 2178.698506 6.83 <.0001 haevelse 1 545.480608 545.480608 1.71 0.1951 Standard Parameter Estimate Error t Value Pr > |t| Intercept 69.72727273 B 5.38675669 12.94 <.0001 grad 0 -19.29948325 B 6.73078030 -2.87 0.0054 grad 1 -33.83236045 B 7.49847230 -4.51 <.0001 grad 2 -25.70376396 B 6.85102247 -3.75 0.0003 grad 3 -6.18622010 B 8.04699047 -0.77 0.4444 grad 4 0.00000000 B . . . haevelse 2 6.13052632 B 4.68955685 1.31 0.1951 haevelse 3 0.00000000 B . . .
Least Squares Means Omfang grad LSMEAN 0 53.4930526 1 38.9601754 2 47.0887719 3 66.6063158 4 72.7925359
omfang haevelse LSMEAN 2 58.8534335 3 52.7229072
13
Enclosure 9
The Mixed Procedure
Model Information Data Set WORK.C Dependent Variable huld_dod Covariance Structure Diagonal Estimation Method REML Residual Variance Method Profile Fixed Effects SE Method Model-Based Degrees of Freedom Metho
Class Level Information
Class Levels Values grad 5 0 1 2 3 4 Dimensions Covariance Parameters 1 Columns in X 6 Columns in Z 0 Subjects 1 Max Obs Per Subject 363 Number of Observations Number of Observations Read 363 Number of Observations Used 349 Number of Observations Not Used 14 Covariance Parameter Estimates Cov Parm Estimate Residual 43.5541 Fit Statistics -2 Res Log Likelihood 2289.6 AIC (smaller is better) 2291.6 AICC (smaller is better) 2291.6 BIC (smaller is better) 2295.5
14
The SAS System The Mixed Procedure Solution for Fixed Effects Standard Effect grad Estimate Error DF t Value Pr > |t| Intercept 25.0000 3.8103 344 6.56 <.0001 grad 0 3.4118 3.8312 344 0.89 0.3738 grad 1 0.4884 3.9409 344 0.12 0.9014 grad 2 -1.0000 4.0164 344 -0.25 0.8035 grad 3 7.0000 5.0405 344 1.39 0.1658 grad 4 0 . . . . Type 3 Tests of Fixed Effects Num Den Effect DF DF F Value Pr > F grad 4 344 4.67 0.0011 Least Squares Means Standard Effect grad Estimate Error DF t Value Pr > |t| grad 0 28.4118 0.4002 344 71.00 <.0001 grad 1 25.4884 1.0064 344 25.33 <.0001 grad 2 24.0000 1.2701 344 18.90 <.0001 grad 3 32.0000 3.2998 344 9.70 <.0001 grad 4 25.0000 3.8103 344 6.56 <.0001 Differences of Least Squares Means Standard Effect grad grad Estimate Error DF t Value Pr > |t| grad 0 1 2.9234 1.0831 344 2.70 0.0073 grad 0 2 4.4118 1.3316 344 3.31 0.0010 grad 0 3 -3.5882 3.3240 344 -1.08 0.2811 grad 0 4 3.4118 3.8312 344 0.89 0.3738 grad 1 2 1.4884 1.6205 344 0.92 0.3590 grad 1 3 -6.5116 3.4498 344 -1.89 0.0599 grad 1 4 0.4884 3.9409 344 0.12 0.9014 grad 2 3 -8.0000 3.5358 344 -2.26 0.0243 grad 2 4 -1.0000 4.0164 344 -0.25 0.8035
grad 3 4 7.0000 5.0405 344 1.39 0.165