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This article was downloaded by: [Dr Kenneth Shapiro]On: 09 June 2015, At: 10:36Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,UK
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If You Knew What WasGood For You! The Value ofEnvironmental EnrichmentsWith Known Welfare BenefitsIs Not Demonstrated by SowsUsing Operant TechniquesMonica Renee Pittman Elmore a d , Joseph PaulGarner a e , Anna Kerr Johnson b , Richard D. Kirkdenc , Brian Thomas Richert a & Edmond Anthony Pajor af
a Department of Animal Sciences , Purdue Universityb Department of Animal Science , Iowa StateUniversityc Department of Veterinary Medicine , University ofCambridge , United Kingdomd University of Illinoise Stanford Universityf University of CalgaryPublished online: 28 Jun 2012.
To cite this article: Monica Renee Pittman Elmore , Joseph Paul Garner , AnnaKerr Johnson , Richard D. Kirkden , Brian Thomas Richert & Edmond AnthonyPajor (2012) If You Knew What Was Good For You! The Value of EnvironmentalEnrichments With Known Welfare Benefits Is Not Demonstrated by Sows UsingOperant Techniques, Journal of Applied Animal Welfare Science, 15:3, 254-271, DOI:10.1080/10888705.2012.683982
To link to this article: http://dx.doi.org/10.1080/10888705.2012.683982
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JOURNAL OF APPLIED ANIMAL WELFARE SCIENCE, 15:254–271, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1088-8705 print/1532-7604 online
DOI: 10.1080/10888705.2012.683982
If You Knew What Was Good For You!The Value of Environmental
Enrichments With Known WelfareBenefits Is Not Demonstrated by Sows
Using Operant Techniques
Monica Renee Pittman Elmore,1 Joseph Paul Garner,1
Anna Kerr Johnson,2 Richard D. Kirkden,3
Brian Thomas Richert,1 and Edmond Anthony Pajor1
1Department of Animal Sciences, Purdue University2Department of Animal Science, Iowa State University
3Department of Veterinary Medicine, University of Cambridge,
United Kingdom
This study assessed the motivation of gestating sows housed in standard, barren
gestation stalls (used for breeding/implantation and/or gestation) for access to
environmental enrichment. Enrichment consisted of a cotton rope or rubber mat in
comparison to positive (additional food when fed at commercial levels) and neg-
ative (empty trough) controls. Although environmental enrichment may improve
animal welfare, sows’ valuation of enrichments is largely unknown. This study
used an operant panel and obtained behavioral measures to quantify motivation.
As indicated by a higher price paid and lower latencies to press the panel and
enter the treatment stall (all comparisons, p < .05), sows demonstrated higher
motivation for food compared with all treatments. Sows housed in gestation stalls
Monica Renee Pittman Elmore is now at the University of Illinois Urbana-Champaign. Joseph
Paul Garner is now at Stanford University. Edmond Anthony Pajor is now at the University of
Calgary.
Correspondence should be sent to Monica Elmore, Department of Animal Sciences, University
of Illinois Urbana-Champaign, 1207 West Gregory Drive, Urbana, IL 61801. Email: MonicaRPE
254
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VALUE OF ENRICHMENTS TO SOWS 255
did not demonstrate high motivation via operant responding for a cotton rope or a
rubber mat; nor did they demonstrate any differences in behavioral measures (all
comparisons, p > .10). Although sows’ motivation for a mat did not differ from
that for an empty trough, previous work has demonstrated the welfare benefits
associated with comfort flooring.
Mounting concern for the welfare of nonhuman animals has led to the banning
of sow gestation stalls in a number of states in America and the European Union
(Council Directive 2001/88/EC). Although stalls have been banned for the entire
length of gestation, their use is still permitted during breeding and embryo
implantation (Council Directive 2001/88/EC) to prevent negative impacts on
sow reproductive performance (Arey & Edwards, 1998; Kongsted, 2004). Stalls
have been criticized for causing both physical and social restriction to the animal
(Chapinal et al., 2010; European Food Safety Authority, 2007; Pajor, 2005) com-
pared with group housing (Barnett, Hemsworth, Cronin, Jongman, & Hutson,
2001; Bracke, Metz, Spruijt, & Dijkhuizen, 1999). In addition, most stall and
group systems lack environmental complexity and stimulation (Broom, Mendl,
& Zanella, 1995; Durrell, Sneddon, & Beattie, 1997). Barren environments have
been associated with impairments in learning (Sneddon, Beattie, Dunne, &
Neil, 2000), increases in negative social interactions: biting (Beattie, Walker,
& Sneddon, 1996), signs of apathy (Arey, 1993), and chronic stress (de Jong
et al., 2000), all of which can lead to detriments in animal welfare. Therefore,
investigation into welfare improvements to barren sow housing, including stalls,
is needed.
Environmental enrichment can be defined as biologically relevant (Würbel &
Garner, 2007) additions or modifications to the environment that allow coping
with stressors by promoting species-specific coping behaviors such as foraging
and rooting (Stolba & Wood-Gush, 1989; Van de Weerd & Day, 2009) and
may be linked to the experience of positive affective states in animals (Boissy,
Manteuffel, et al., 2007).
It is important to note that not all resources provided to animals are en-
richments, only those that meet the criteria outlined above. Enrichments may
improve the welfare of sows housed in barren environments by providing op-
portunities for natural behaviors such as foraging (Feddes & Fraser, 1994;
Tuyttens, 2005; Whittaker, Edwards, Spoolder, Lawrence, & Corning, 1999),
which may reduce chronic hunger in restricted-fed sows by increasing gut fill
(e.g., straw; Fraser, 1975) and can lead to reductions in abnormal behavior (e.g.,
stereotypic; Fraser, 1975; Spoolder, Burbidge, Edwards, Simmins, & Lawrence,
1995). In addition, physical and thermal comfort may be improved by the
provision of straw bedding or rubber mats (Boyle, Regan, Leonard, Lynch,
& Brophy, 2000; Elmore, Garner, Johnson, Richert, & Pajor, 2010; Tuyttens,
2005). The motivation of sows for environmental enrichments is largely un-
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256 ELMORE ET AL.
known but is essential knowledge for developing housing that promotes animal
welfare.
Motivation studies can identify resources of value to animals (Dawkins, 1983,
1990) that lead to science-based recommendations, and, ultimately, to improve-
ments in animal welfare. The willingness of an animal to “pay” for access to
a resource is an index of how the animal “feels” about that resource (Dawkins,
1990). This knowledge will become increasingly important as scientists strive
to measure affective states in animals (Boissy, Arnould, et al., 2007; Boissy,
Manteuffel, et al., 2007; Mendl, Burman, Parker, & Paul, 2009). Investigation
into the motivation of animals frequently utilizes measures that are derived from
human economic theory, with elasticity of demand being the most commonly
employed measure in animal studies (Holm, Jensen, & Jeppesen, 2002; Matthews
& Ladewig, 1994; Sherwin & Nicol, 1997). Due to the criticisms against the use
of elasticity (Kirkden, Edwards, & Broom, 2003; Mason, McFarland, & Garner,
1998), reservation price (or the highest price paid) was adopted in this study; it
is considered a more robust and valid measure of animal motivation (Kirkden
et al., 2003; Mason, Cooper, & Clarebrough, 2001; Mason et al., 1998).
The aim of this study was to compare the motivation of gestating sows housed
in standard, barren gestation stalls for access to one of four resources: (a) cotton
rope (enrichment); (b) rubber mat (enrichment); (c) additional food (positive
control) when fed at commercial levels, �30–60% of ad libitum intake (Barnett
et al., 2001; Kirkden & Pajor, 2006a); or (d) an empty trough (negative control).
A cotton rope allows for the expression of oral behaviors observed during for-
aging (Feddes & Fraser, 1994), without complications to existing infrastructure,
which can be problematic when providing other substrates (e.g., straw in a liquid
manure system). Rubber mats can increase flooring and thermal comfort (Boyle
et al., 2000; Tuyttens, Wouters, Struelens, Sonck, & Duchateau, 2008) and can
improve welfare by, for example, reducing lesions (Elmore et al., 2010). We
hypothesized that sow motivation would be affected by the resource provided.
Specifically, we reasoned that sows would show high motivation for food, a
known valued resource, especially when feed-restricted (Matthews & Ladewig,
1994; Patterson-Kane, Pittman, & Pajor, 2008). We further hypothesized, based
on similar negative controls (Cooper, 2004; Mason et al., 2001), that sows
would show low motivation for an empty trough, an assumed unvalued resource.
We predicted that motivation for enrichments of value to the sow would be
significantly different from motivation for an empty trough. Since controls can
act as both low and high comparators to aid in the assessment of resource
value (Cooper, 2004), it is important to use them in animal motivation studies.
In addition, we hypothesized that the behavior of the sows would vary due to
treatment; where sows provided with a cotton rope would show an increase in
general activity due to an increase in foraging-type behaviors (Feddes & Fraser,
1994), sows provided with a rubber mat would show an increase in resting
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VALUE OF ENRICHMENTS TO SOWS 257
behaviors due to an increase in flooring comfort (Boyle et al., 2000; Gravas,
1979; Tuyttens et al., 2008).
MATERIALS AND METHODS
All experimental procedures were approved by the Purdue University Animal
Care and Use Committee. This experiment was conducted daily from 08:00 hr–
12:00 hr during November of 2008 through August of 2009 at the Purdue
University swine farm.
Animals and Husbandry
A total of 40 enrichment naïve Landrace � Yorkshire multiparous (2.15 ˙ 0.36
parities; mean ˙ standard deviation [SD]) sows were used in this study. The
sows were confirmed pregnant via ultrasound (performed by a trained swine
farm employee) at 35 days postbreeding, were moved from gestation housing
(either stalls or groups) to a separate test barn, and were given 24 hr to habituate
to their surroundings prior to the start of the experiment. All sows had previous
experience with both group housing and gestation stalls. The sows had access
to water ad libitum from a nipple drinker and were fed approximately 2.3 kg of
sow gestation diet (12.6% CP and 0.55% lysine) each morning. To enhance the
external validity of our findings, sows were not fed ad libitum but were feed-
restricted to commercial levels. Artificial lighting was provided continuously
for videorecording purposes (infrared was not possible in the barn), air quality
was controlled by a negative pressure exhaust system, and the average room
temperature was recorded at the start of each day and varied due to season
(20.6 ˙ 1.7ıC; mean ˙ SD). Farm employees observed the sows at 08:00 hr
and 15:00 hr daily for overall health.
Treatments
Sows were fed and tested in the same standard, barren gestation stall (hereafter
“test stall”). The test stalls (2.13 m L � 0.61 m W) were constructed of steel and
were positioned over fully slatted concrete flooring. In front of each test stall
was an alleyway (measuring approximately 4 m in length) that led to a separate
stall where the resource was provided (hereafter “treatment stall”; Figure 1). The
alleyway, constructed of opaque plastic boards, created a visual barrier for the
sows. On completion of the operant task, the sow gained immediate access to
the resource by walking forward and entering the treatment stall. Due to space
constraints, the provision of a full-length rubber mat in front of the stall was
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258 ELMORE ET AL.
FIGURE 1 Schematic of room layout with four testing stations. At each testing station,
there were two test sows (T1 and T2), each with her own test stall and treatment stall (where
the assigned resource was provided). However, both sows at each station used the same
operant panel for testing. Sows were tested in homogenous treatment pairs. Treatments were
rotated and balanced across replications to account for location in the room (color figure
available online).
not feasible; a separate treatment stall was required. Resource provision was
standardized to allow for proper comparison against “positive” and “negative”
controls; therefore, all treatments were accessed in a separate treatment stall via
an alleyway. Due to this standardization, sow motivation to exercise, novelty of
the treatment stall, and other potential confounds were controlled for by testing
sow motivation for the negative control (empty trough).
Sows were assigned to one of four treatments at the start of the experiment
(n D 10 sows per treatment): (a) an empty trough in a standard concrete stall
(negative control), (b) cotton rope (environmental enrichment), (c) rubber mat
(environmental enrichment), or (d) additional food (positive control). Food was
considered a positive control in this study because sows were fed at commercial
levels (�30–60% of ad libitum intake; Barnett et al., 2001; Kirkden & Pajor,
2006a), which likely results in feelings of hunger and high motivation for
additional food. The sows remained on the same treatment for the duration
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VALUE OF ENRICHMENTS TO SOWS 259
of the experiment and were not tested on all treatments due to time constraints
imposed by gestation. For the rope treatment, one cotton rope (2.54 cm W,
30.48 cm L, with ends unbraided) was attached with a hose clamp to the bars of
the stall and was allowed to hang freely. The cotton ropes were replaced during
testing if more than half of the length (approximately 15 cm from the bottom)
or half of the diameter (approximately two of the three unbraided sections) was
absent or excessively damaged. In addition, a new rope was provided at the
start of each testing series (see section Experimental Apparatus and Procedure)
and for each new test subject. For the mat treatment, a perforated rubber mat
(1.83 m L � 0.61 m W, hole diameter �2.54 cm) spanning the length and width
of the stall (minus the area covered by the feed trough) was provided to the
sows. For the positive control, a single 0.91 kg portion of the sows’ standard
gestation diet was used as the reward. The enrichments were rotated between
replicates to balance for location in the room.
The room layout used in this experiment consisted of four test stations in the
corners of the room, with two sows per station (Figure 1). Both sows at each
station were test subjects, but the testing times for the sows were staggered 1 hr
apart from each other. The sows were not tested in isolation; they were allowed
olfactory and auditory contact with their respective neighbors. However, a visual
barrier (approximately 1 m L � 1 m H) was installed between the two stalls
to reduce any disruption caused by the companion during testing; this barrier
was not present between the treatment stalls. In addition, because barriers were
not placed in the front of the test stalls, sows had limited contact with one
another when moving from the test stall to the treatment stall. Sows were tested
in homogenous treatment pairs to avoid the influence of a neighbor’s treatment
on sow motivation (e.g., the smell of food when working for an empty trough).
Treatments were rotated and balanced across replications to account for location
in the room.
Experimental Apparatus and Procedure
Sows were allowed 1 hr each morning to consume their daily meal in the test
stall, and any unconsumed feed was removed prior to testing. Sow motivation
for access to the resource was tested 7 days per week following feeding. At the
start of testing each morning, the sow’s feed trough was removed and replaced
with the operant panel. The operant gate consisted of a stainless steel panel
(13 cm L � 10 cm W) attached to a modified gestation-stall, food-trough frame,
which was positioned at the height of the sow. The panel was locked in place
and could not be pressed until the gate had been fitted to the stall. A light cue
(above the snout panel) signaled when the panel was unlocked. A panel press
was registered by a computer when the sow had depressed the panel with her
snout.
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260 ELMORE ET AL.
Prior to testing, sows were trained to press the operant panel (up to 10 presses)
with food as the reward (daily meal; 2 days). Following this initial training, their
assigned resource (empty trough, cotton rope, rubber mat, or food) became
the reward for 5 days of additional training (previously described: Elmore
et al., 2011). After completion of training, sows were permitted access to the
enrichments only after “paying” for access via presses on the operant panel.
Therefore, a traditional closed economy was employed in this study (Cooper,
2004; Mason et al., 1998).
Sows were placed on an ascending series of fixed ratio (FR) schedules, where
the number of panel presses required by the sow increased by 50% each day
after FR 10 (FR 1, 10, 15, 23, 35, 53, 80, 120, 180, 270, 405, 608, 912, 1368,
and 2052). Sow testing order was varied to reduce the impact of the neighbor’s
actions on the sows’ motivation and operant responding. Sows were given 1 hr
each day to complete the required FR schedule. If the sow succeeded, the panel
swung open, and she was permitted immediate access to the resource via an
alleyway (described earlier). The sows were given 5 min to enter the treatment
stall on their own. After this time, the experimenter escorted the sow to the
treatment stall by (a) a hand on her back or (b) if necessary, a herding board.
The sows were then locked inside the treatment stall with a rear gate until the
next day; then testing was repeated (providing a maximum of 23 hr access to
the resource). Resource access times varied depending on the testing order of
the sows and the time it took each sow to reach the required FR schedule.
If the sow failed to reach the required FR schedule within 1 hr, she remained
in the test stall, was not permitted access to the resource, and testing ceased.
The following day, the sow was given a second chance to reach the required
FR schedule. If she succeeded, she was permitted access to the resource, and
testing continued according to the prescribed series of FR schedules. If she
failed a second time, testing ceased permanently for that series. Two separate
series were performed to allow the sows more time to familiarize themselves
with the operant procedure and the resource. The highest price paid represented
the sows’ motivation for the resource. It was calculated from the second series
and was defined as the highest FR schedule that the sow successfully achieved
prior to cessation of pressing (Kirkden & Pajor, 2006b). For additional details
on the training and testing procedures used in this study, refer to Elmore et al.
(2011).
Behavioral Observations
The behavior of the sows during operant response and resource access was
recorded continuously throughout the experiment using time-lapse video. The
sows were marked with livestock paint (All-Weather® Paintstik®) for identifica-
tion on the video. The paint was reapplied as needed. One black/white camera
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VALUE OF ENRICHMENTS TO SOWS 261
(Panasonic WV-BP330, Secaucus, NJ) was mounted on the ceiling above each
pair of test stalls and treatment stalls. The output was recorded using a time-
lapse VCR (Panasonic AGTL950P, Secaucus, NJ) and a multiplexer (Panasonic
WJ-FS216, Secaucus, NJ) in 48 hr mode. All behavior data on the day of highest
price paid for the resource were quantified by one experienced observer.
Latency to press the operant panel, defined as the time (s) between operant
panel attachment and the test sow’s first press, was collected as an additional
measure of motivational strength. Resource use was quantified as (a) general
activity (to measure rope use) and (b) resting behavior (to measure mat use).
General activity (defined as drinking, eating, and manipulating the rope or stall
components: biting, nosing, and rooting) was quantified using 1-0 sampling
every 1 min for a maximum of 23 hr (from the start of resource access until the
following morning at feeding). Finally, resting behavior (defined as kneeling,
sitting, or lying) was quantified using this same procedure. However, all sow
behaviors were not scored (e.g., standing inactive); they were not of interest to
the research question.
Statistical Analysis
Data were analyzed as a generalized linear model (GLM) or as a repeated
measures mixed model (REML), where appropriate, in JMP 6 for Windows
(2005). Data were transformed as necessary to meet the assumptions of GLM
or REML: homogeneity of variance, normality of error, and linearity (Grafen
& Hails, 2002). Significant results (p < .05) were examined with post hoc tests
to further describe the relationship between the tested interactions. Statistical
trends were considered as p < .10. Equivalence tests were performed to confirm
sufficient statistical power for negative results of importance to our hypotheses.
Unless indicated, numerical data are presented as raw means ˙ SE within the
text. For graphing purposes, data are presented on transformed scales where
necessary.
Motivation data. The highest price paid, representing motivation for the
resource, was quantified as the highest FR schedule that the sow successfully
completed. The model used was treatment, blocked by group (accounts for
variability due to replication); location (stall location within the testing station);
and testing order (first or second sow to test). We used equivalence tests of
the Tukey’s 95% confidence interval to test nonsignificant motivation results for
sufficient power. We wished to detect a twofold difference between treatment
means, in particular, compared with the negative control (empty trough). In
addition, the highest number of presses (regardless of schedule completion) was
analyzed; however, this had no effect on statistical outcomes (data not shown)
and was therefore not included within the manuscript. Latency to press the
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262 ELMORE ET AL.
panel and latency to enter the treatment stall were also analyzed. Latency to
press the operant panel acted as an indicator of motivation to work on the
operant, and latency to enter the treatment stall acted as an indicator of certainty
and anticipation for the resource. The prediction was that lower latencies would
represent an increased motivation for access to the resource. Due to video error,
latency to press the panel for 5 sows was missing (one food, two mat, and two
empty trough). The model used for latency to press the panel was the same
as described earlier. Latency to enter the stall was the same as earlier with the
addition of latency for food (during training) as a covariate. Differences in the
highest price paid due to series (1 vs. 2) were analyzed as an REML, where
the sow was treated as a random effect and nested within treatment with the
interactions of treatment and series. All analyses required log transformation.
Resource use: General activity and resting behavior. Both the amount
and pattern of general activity and resting behavior exhibited by sows with
access to an empty trough (negative control) was used as a comparator for all
other treatments. We were most interested in the sows’ behavior (a) while first
accessing the resources and (b) the next morning prior to their being returned to
the test stall for feeding, which are known periods (based on previous data) of
high enrichment use (Elmore et al., 2011). As sow access times to the resource
varied (see section Experimental Apparatus and Procedure), this second measure
could not be collected at the same time point (19:30–21:30 hr) for all sows.
Therefore, raw data were collated in two ways: (a) from the start of resource
access (to test for differences in initial use) and (b) backward from the time since
resource access ended (to test for differences prior to feeding/resource removal).
When analyzed, both analyses showed nearly identical results (data not shown).
Therefore, to avoid repetition within the manuscript, only the general activity and
resting behavior for sows from the start of resource access are presented in the
article. Data were lumped into 1 hr bins for the entire access period (maximum
23 hr); the longest access period that was common for all sows (20 hr) was used
for analysis, and the remaining data after this time point were removed. Data
were analyzed as an REML, where the sow was treated as a random effect and
nested within treatment with all the interactions of time and treatment. Data for
general activity required square root transformation; data for resting behavior
required angular transformation to meet the assumptions of REML.
RESULTS
Motivation
The highest price paid was significantly affected by treatment (GLM: F3;32 D
6.27, p D .002; Figure 2), with sows showing higher motivation for food
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VALUE OF ENRICHMENTS TO SOWS 263
FIGURE 2 Comparison of the motivation (defined as highest price paid) of gestating sows
for access to one of four resources (Food D positive control, Cotton Rope or Rubber Mat D
environmental enrichments, Empty Trough D negative control; n D 10/treatment) in a stall.
LSM ˙ SE are plotted. Significant Tukey comparisons are indicated by columns not sharing a
common letter (p < .05). To illustrate sufficient power for negative results, the upper limit of
the Tukey’s 95% confidence interval for the control treatment (empty trough) was determined
and is represented by a dashed line on the graph. Data are transformed and presented on a
log scale.
compared to a cotton rope (p D .02), a rubber mat (p D .003), and an empty
trough (p D .006). Equivalence tests revealed that we were able to detect a 1.69-
fold difference between treatment means and therefore had sufficient power in
this experiment. Latency to press the operant panel was also affected by treatment
(GLM: F3;27 D 6.51, p D .002; Figure 3), where sows working for food showed
a reduced latency to press the panel compared with a cotton rope (p < .001).
There was also a trend for sows working for food to show a reduced latency
to press the panel compared with a rubber mat (p D .06) and an empty trough
(p D .08). However, no other treatment differences were found (all comparisons,
p > .10). Latency to enter the treatment stall was affected by treatment (GLM:
F3;31 D 29.43, p < .001), where sows accessing food entered the stall much
sooner (17.0 s ˙ 6.76) than for all other resources (Rope: 182.0 s ˙ 43.04; Mat:
243.90 s ˙ 32.99; Trough: 223.10 s ˙ 38.72; all comparisons, p < .05). No other
treatment differences were found (all comparisons, p > .10). Series affected the
highest price paid (REML: F1;36 D 14.31, p < .001), where sows showed higher
operant responding in Series 2 (292.33 presses ˙ 64.52) compared with Series 1
(238.78 presses ˙ 84.66). However, the interaction of series and treatment was
not significant (REML: F3;36 D 1.01, p D .40).
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264 ELMORE ET AL.
FIGURE 3 Comparison of the latency to press the operant panel(s) by gestating sows for
access to one of four resources (Food D positive control, Cotton Rope or Rubber Mat D
environmental enrichments, Empty Trough D negative control; n D 10/treatment) in a stall.
LSM ˙ SE are plotted. Significant Tukey comparisons are indicated by columns not sharing
a common letter (p < .05). Data are transformed and presented on a log scale.
Resource Use: General Activity
No treatment differences were found in general activity (Food, 3.82% of obser-
vations ˙ 0.12; Rope, 10.03% ˙ 0.11; Mat, 6.56% ˙ 0.14; Trough, 7.22% ˙
0.14, back transformed data; REML: F3;31 D 2.11, p D .12) or the interaction
of general activity and time (REML: F60;619 D 1.11, p D .28). However, there
was a time effect (REML: F20;619 D 27.22, p < .001; Figure 4), where general
activity was highest during the first 2 hr after resource access and the last 1 hr
before resource access ended, regardless of assigned treatment (all comparisons,
p < .05).
Resource Use: Resting Behavior
Similar to general activity, no treatment differences were found in resting be-
havior (Food, 95.77% of observations ˙ 0.29; Rope, 87.31% ˙ 0.26; Mat,
92.26% ˙ 0.32; Trough, 90.63% ˙ 0.32, back transformed data; REML: F3;31 D
1.55, p D .22) or the interaction of resting behavior and time (REML: F60;620 D
0.94, p D .60). However, there was a time effect (REML: F20;620 D 24.21,
p < .001; Figure 5), where, regardless of treatment, resting behavior was lowest
during the first 5 hr after resource access and the last 2 hr before resource access
ended (all comparisons, p < .05).
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FIGURE 4 Change in general activity behavior over time since start of treatment access
(h), all treatments combined (n D 40). LSM ˙ SE are plotted. Data points that were
significantly different from the mean are indicated by *p < .05. Data are transformed and
presented on a square root scale.
FIGURE 5 Change in resting behavior over time since start of treatment access (h), all
treatments combined (n D 40). LSM ˙ SE are plotted. Data points that were significantly
different from the mean are indicated by *p < .05. Data are transformed and presented on
an angular scale.
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266 ELMORE ET AL.
DISCUSSION
This study represents one of the first attempts to assess the value of enrichments
to gestating sows housed in standard, barren stalls, where the motivation of
sows for a positive control (additional food when fed at commercial levels),
negative control (empty trough), or enrichments (cotton rope or rubber mat)
were compared. As predicted, sows showed the highest motivation (as indicated
by the highest price paid and a reduced latency to press the operant panel or
enter the treatment stall) for access to food. The motivation of sows for access
to a cotton rope or a rubber mat did not differ significantly from that for an
empty trough, indicating that these enrichments were not highly valued by the
sows in this study.
A previous study—using the same operant equipment, training, and testing
procedures—assessed the motivation of sows for access to a food reward at
various hunger levels, creating a food-based reference scale (Patterson-Kane,
Kirkden, & Pajor, 2011). According to this scale, sows in the present study
showed high levels of motivation for both enrichments and an empty trough,
responding at similar rates to sows who had consumed 0–25% (approximately
0–2 kg) of their ad libitum intake level. However, this finding is likely due
to the rewarding nature of locomotion and investigation to stall-housed sows
and an association between the trough and access to food by feed-restricted
sows, introduced by the operant procedure and controls (see later for further
discussion).
The majority of work concerning environmental enrichment for swine has
focused on grow/finish pigs (Van de Weerd & Day, 2009) but can provide
insight into enrichments that can be beneficial to sows as well. In a study by
Van de Weerd, Docking, Day, Avery, & Edwards (2003), researchers found that
pigs interacted most with enrichments that stimulated foraging and exploratory
behavior, including odorous, deformable, chewable, and destructible enrich-
ments. This finding mirrored those of Feddes & Fraser (1994), who found that
cotton ropes elicited higher responses from piglets when the end was exposed
(allowing greater destructibility) compared with a loop or a rubber strip. This
study represents one of the first attempts to provide a cotton rope to sows
as a form of environmental enrichment. Due to additional labor requirements,
disease considerations, and current difficulties for the liquid manure-handling
systems (Day et al., 2002; Tuyttens, 2005), straw is not commonly provided
in U.S. swine systems. A cotton rope may offer an alternative to straw and
allow for the expression of oral behavior (chewing) in intensive systems, which
may be especially important for sows who are feed-restricted. However, based
on the behavior and motivation measures gathered in this study, a cotton rope
does not appear to be a valuable enrichment to gestating sows housed in stalls.
For commercial sows fed a restricted diet, �30–60% of their ad libitum intake
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VALUE OF ENRICHMENTS TO SOWS 267
(Barnett et al., 2001; Kirkden & Pajor, 2006a), the expression of the appetitive
component of foraging behavior—without the consummatory component (lead-
ing to gut fill and satiety; Rushen, 1984)—may be insufficient to satisfy the
needs of the sow (de Jonge, Tilly, Baars, & Spruijt, 2008; Hughes & Duncan,
1988), thus reducing motivation for a cotton rope. It is interesting to note that
the motivation for a cotton rope varied across sows, with some sows showing
very high motivation for rope access. This indicates that a cotton rope may be
a highly valued enrichment to some, but not all, sows. However, the feasibility
and economic impact of tailoring enrichment provision for individual sows is not
practical in commercial conditions; therefore, an environmental enrichment that
is valued by a wider proportion of sows should be identified for implementation
on farms.
Previous work has shown that sows prefer to rest on rubber mats (Elmore
et al., 2010; Gravås, 1979; Tuyttens et al., 2008) and that mats can lead to
many benefits for sow welfare, including an increase in the ease of getting up
and down (Elmore et al., 2010), reduced slipping (Boyle et al., 2000), fewer
lesions (Elmore et al., 2010), and a reduction in lesion healing time (Zurbrigg,
2006). However, based on the motivation and behavior measures in this study,
sows did not value access to a rubber mat in a stall. Although the empty trough
treatment was added to control for potential confounds of the operant procedure,
the opportunity for locomotion in the alleyway (measuring �4 m in length)
for all treatments may have been rewarding enough to overshadow any slight
preferences the sows had for a rubber mat. In addition, sows were permitted
5 min to enter the stall on their own, allowing them to investigate the alleyway
and, potentially, the other test sow prior to being locked in the treatment stall.
Again, the rewarding nature of investigation may have overpowered any slight
preferences for the mat.
In addition, another possible explanation may be the ecological constraints
on learning introduced by the operant used in this study (Young, Macleod, &
Lawrence, 1994). Sows were required to press the operant panel with their snouts
to gain access to the resource, which lends itself nicely to resources that fulfill
a similar motivation (substrates to root and forage) but may be counterintuitive
for other resources (comfort flooring). Although the operant panel was artificial
(Cooper, 2004), we also incorporated a naturalistic task of walking to access all
resources. However, this may have been insufficient to overcome the constraints
on responding imposed by the operant when working for the rubber mat.
Finally, the lack of motivation observed for a rubber mat may reflect a
fundamental shortcoming of using operant conditioning techniques. When using
these techniques, we are asking the sow to make a decision in the short term
based on long-term benefits. This may not be problematic for resources that
have obvious immediate consequences (e.g., food and gut fill) but may be more
difficult for resources whose benefits are not as immediately forthcoming (e.g.,
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comfort flooring leading to long-term improvements in leg health). In future
studies, testing sows with known leg problems (lameness or hoof lesions) may
increase the sows’ willingness to work on an operant panel to gain access to
this flooring substrate.
CONCLUSION
Gestating sows housed in standard, barren gestation stalls did not demonstrate
high motivation via operant responding for either a cotton rope or a rubber mat,
or any differences in behavior. Although motivation did not differ from that for
an empty trough, previous work has demonstrated health and welfare benefits
associated with the provision of a rubber mat. As animal welfare scientists
strive to measure affective states in animals to improve their welfare, further
investigation into both the value of enrichments to sows and techniques to
understand the sows’ perspective will become increasingly important in the
literature.
ACKNOWLEDGMENTS
This project was supported by the National Research Initiative of the U.S.
Department of Agriculture, Cooperative State Research Education, and Exten-
sion Service, Grant 2005-35204-15215. We thank Dick Byrd and the Purdue
University swine farm staff for their efforts in the construction of experimental
apparatuses. We also thank the following people for their assistance: Dr. Emily
Patterson-Kane (advice on experimental methods), Barry Elmore (installation
and repair of video equipment), Dr. Eric Furgason (repair of operant equipment),
Melissa Elischer (aid in the collection of motivation data, and behavior video
analysis), and Dr. Don Lay (comments on the manuscript).
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