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FEED CONVERSION AND FEEDING BEHAVIOUR IN LAYING HENS

J. F. Hurnik

Dept. of Animal and Poultry Science

Guelph University, Guelph, Ontario, Canada, NIG 2WI

Introduction:

T_e high proportion of feed costs in total operating expenses (1,2,6)

indicates that the utilization of feed by the birds is closely related to

the profitability of >oultry operations. The relationship between feed

conversion (expressed as a ratio between weight units of feed consumed per

weight unit of product) and profitability (defined as an increment .of total

income over total costs) is especially important in circumstances where the

total labour costs and fixed costs approach the essential minimum. The same

is true where supply controls are applied and total profit cannot be raised

by production expansion.

In a partially arbitrary way the relationships between profit and feed

conversion is shown in Fig. I. The pertinent calculations were conducted

using constant price of feed and eggs and uniform distribution of all other

costs, except feed costs. Both independent variables, which influence the

response surface, were chosen within an experimentally documented range

(14,15).

Feed conversion:

Feed conversion is a resultant of a broad scale of variables embodied in

feed intake, metabolic efficiency and production performance. Equally to any

other biological trait or trait combination, feed conversion r6flects the

whole Complex array of genetic information controlling each of the participating

variables. In a biologically tolerable environment, both the genetic information

and the environmental condition for their physical and functional realization

differ among individuals and the resulting variation is proportional to the role

of these two basic biological agents.

Prerequisites for the reliable detection of individual feed conversion

ratios are the amount of egg mass produced and theamount of feed consumed. It

is simple to obtain the initial information for a precise definition of egg

mass production. Surprisingly little is known however, about the feed consumption

of individual hens. This probably stems from the fact that in the past price of

feed and the proportion of feed costs to total costs were lower and the amount

of labour required for the individual measurements of feed consumption _elatively

high. Due to the latter reason researchers intended to substitute the direct

measurements of feed consumption by other easily obtainable variables (e.g.

body weight, weight gains etc.) A principal contribution in this field was

made by Nordskog (20) who predicted income over feed costs without feed

consumption data. It may be noted however, that an approximation based on

correlated trait(s), sucb as metabolic rate estimated as a function of body

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weight (16), smoothes the individual variation in ability to metabolize

nutrients, ignores the behavioural characteristics (e.g. waste of nutrients

due to hyperactivity, frustration etc.) and therefore overemphasizes the role

of the applied independent variable. Obviously, any inaccuracy in thedetection

of individual variation shifts the proportions of contributary components of

total variance and thus alters all of the derived parameters (e.g. intraclass

coefficients and heritabilities). This then detracts from the reliability ofthe estimated genetic potential of selected birds.

Feed consumption:

Feed consumption is basically a behavioural response to a homeostatic

drive, activated by disequilibrium in a metabolic state of the organism. The

character of this drive is essentially primary, which indicates that it is

universal in any given species for which there is a physiological basis and

its occurrence in natural circumstances is independent of learning.. In a

simplified way the cyclical occurrence of feeding can be explained as follows:

Cellular metabolism alters the level Of glucose in the blood, this change is

detected in the hypothalamus, and through appropriate cerebral centers a

coordinated behaviour is activated which has a potential to reduce the drive

(e.g. 19). An accurate measurement of the internal processes or states which

govern ingestive behaviour is technically impossible to conduct. For this

reason researchers concentrate on the observable behav£oural patterns and

physiological changes associated with feed deprivation and/or ingestion ofnutrients (7).

Schematically, three kinds of control mechanisms are involved in feedingbehaviour.

i) Prelngestive mechanisms, which control the activation of feeding.

2) Ingestive mechanisms, which control the feeding responses.

3) Postingestive mechanisms, which control the state and duration ofsatiation.

At the operational level each of the three stages can be associated with

distinct stimuli and corresponding behavioural repetoires. The variety of these

stimuli indicates, that the simplified def.[nition of feeding behaviour - as an

observable response to metabolical needs - does not satisfactorily reflect the

motivational complexity which influences the feed intake, as it ignores theextrinsic factors involved. In spite of the central role of metabolic controls

as biological safeguards for instinctive _ngestion and its rhythmical occurrence,

behavioural manifestations of appetite, feeding and satiation can be altered

by various techniques of psychological manipulation. For example, feeding

behaviour can be influenced by external stimulation of the brain (2,3), exogenous

application of chemical compounds (3,18), physical pressure in a food reservoire

(22) by a lighting regime (24), social facilitation (i0), social hierarchy (25),

via the effect of ovlposition on preferential intake of nutrients during the day

(5,11), by natural preference for feed and feeder colour (12), through sensitivity

to feeder patterns (13), and conditioning to flashing lights (17) etc. These few

examples demonstrate the susceptibility of feed consumption to external andinternal stimuli and this fact has to be taken into consideration if accurate

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data are required. It is especially important in selection work, where tile

advantages of exact evaluation analyses are often masked by inadequate accuracyof the input information.

Mechanical devices to measure individual feed consumption should be

psychologically neutral, avoiding both the repulsion or the attraction of

birds. The separation of individual feeding spaces should deviate minimally

from the feeders expected to be used by producers and should not prevent

visual contact between birds. Visual contact across adjacent cages and across

opposite rows is necessary for a standard level of social facilitation of

feeding responses. The process of feed weighing should be arranged to minimize

any positive or negative stimulation. At the present time this cannot be done

without some additional operations to common routines. In such a case, prior

to the commencement of the data collection period, proper attention has to be

paid to achieve an adequate level of habituation in the birds. The length of

time and the number of preliminary trials required for such habituation dependson the overall character of those activities.

An important prerequisite for a high quality of input information about

individual feed consumption is the number of repeated measurements and their

chronological distribution. Generally, the Objective of the observer would

be to minimize the number of measurements without any detrimental effect on

the precision of the estimates representing each bird. Results from a study

conducted on 270 laying hens (9) indicate that the accuracy obtained from 96

measurements per hen (two consecutive days recorded over a pFoduction period of

48 wks) could be reduced within an acceptable limit (_ = .05) to 12 representative

measurements. (Table i). Both, an auto-covariance method (4) and stepwise re_

gression procedure (8) suggested that these 12 measurements should be spaced

regularly over the entire observation period.

Another regression analysis of data from this study revealed that the

largest proportion of the variability in individual feed consumption during

the first production year (Fig. 2) was relatedto egg mass produced (36%), followed

by body weight measurements (30%), which included weight gains, fat pad, visceraand liver weights. Behavioural variables accounted for an additional 12%.

(These variables were defined as arcsin transformed proportions of eating,

drinking, resting and standing time, recorded during two hours (i0:00 - 12:00 hrs)

for one in every 14 days of production). Nevertheless over 20% of the variation

in individual feed consumption remained unexplained. It might be assumed that

the differences in individual metabolic efficiency, acclimation to various

stressors and in the 'wastage' of nutrients for non-profitable hyperactivitiescould account for a substantial part of this residual variation.

The relationship between feed consumption and feed conversion:

The frequency distribution of individual feed conversion ratios revealed

significant positive skewness (Fig. 3). For this reason all further comments

refer to in transformed ratios.

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Naturally, the accuracy of feed conversion estimates is very high(R2 = .995) if all three basic traits - egg number, egg weight and feed

consumption, are available. In such a case, the most influential trait

controlling the variation in feed conversion is the number of eggs laid

(51%) followed by feed consumption (31%) and average egg weight (18%). (As

shown in Table 2 these values include quadratic effects of egg productionand feed consumption).

When feed consumption was deleted from the set of available variables,

the accuracy of feed conversion estimates was noticeably lower (R2 = .827).

The substitutes, selected in descending order via a stepwise regression pro-

cedure were: the body weight at the end of laying period (71 w_s of age), the

weight of abdominal fat pad, body weight at the beginning of laying period(23 wks of age), and liver weight.

Some of the above selected varlables are time consuming and thus costly

to obtain. _hen, for this reason, the set of available traits was reduced,

to consist of only "easily" measured variables,^the resulting accuracy of

the estimates was inevitably further lowered (Rz = .795). Table 3 shows

both the sequence of contributing traits to feed conversion estimates and

their relative importance.

The relationship between feed conversion and profitability:

The economic assessment of declining feed conversion estimates requires

a complex evaluation of the relationships between egg price, feed price and

other costs expected in the future, toward which the breeder orients his

selection objectives. This is naturally a very difficult task. Based on

present economic parameters individual profitabilities of the discussed group

of laying hens varied between -$8.65 to $5.20. The frequency distribution

was negatively skewed and the overall mean was $1.65.

Since certain costs, such as housing or overhead expenses are relatively

constant for all hens, the principal traits which contribute to the variability

in profit are the same as those which control feed conversion. Among them,

the most important was again, egg production (49%), followed by average eggweight (30%) and feed consumption (21%).

A characteristic of basic economic interest in poultry operations is the

development of cumulative profitability during the production period, and the

time taken to reach the break-even point, where the returns equal the costs.

The mean break-even point occurred during the 26th week of the experiment, when

the hens were 49 weeks old. The magnitude of gradual changes in cumulative

profitabilities and their increasing variability, could be used in determining

the economic effects of elimination or replacement of unprofitable hens. In

a simplified situation, where variation due to location and genotype, changes

in prices, the difficulty of obtaining individual performance data, and some

managerial problems are ignored, the follo_,_ing conclusions can be made in relation

to three arbitrarily chosen groups of unprofitable hens,

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i) hens whose expected performance will fall between the break-even

point and $0.50 loss should not be removed,

ii) hens whose predicted performance will cover the maintenance costs,

but not the initial cost of the pullet, should not be removed,

except when replaced before the 22nd week of production (45 wks old),

ill) hens which lay no eggs, but survive, should _e replaced before the

22nd week of production. Thereafter, such hens should simply beremoved.

Assumingthat the replacement hens will exhibit the cumulative profitability

curve of the average hen, they will not be able to produce a profit as such.

Substitution will reduce only the expected loss of the original hens, and thus

contribute to the better overall profitability of the group.

The comparison of observed percentile distributions implies tl{at some

improvement can b@ gained when birds are ranked and selected according to the

magnitude of their absolute profit instead of egg production alone. This

is especially valid if high selection intensity is applied. For example, when

the profit from the top 10% of egg layers was calculated, it accounted for only

88% of that obtained when the top 10% of birds were selected according to theirindividual profit ($3.39 vs. $3.85). On the other hand the best 10% of hens

selected according to feed conversion (Fig. 4) did not show the highest totalincome but provided the best return on investment (%).

Summary: ..

The results from the discussed studies can be summarized as follows:

i) The amount of feed costs represents the largest single component of

total operating costs in contemporary poultry industry. For this

reason Feed conversion, expressed as a ratio Of units of feed consumed

per unit of product, became an important production parameter.

2) An accurate determination of individual feed conversion requires

individual Feed consumption measurements. The utilization of related

variables provides only a partial substitution of feed consumption,

which could be a serious obs_cle for the precise detection of genetic

potentials of birds and makimalgenetic progress, should feed conversion

be subjected to a direct selection.

3) A reliable measurement of individual feed consumptions cannot ignorethe behavioural characteristics of birds and their responsiveness to

the stimulation caused by the process of data collection.

4) Birds which were the best in feed conversion provided the greatest return

on money invested.

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Bibliography

(I) Adolph, R.H., 1975. Changes in cost factors of poultry egg production.Poult. Sci. 54:1725 (Abstract).

(2) Adolph, R.H.,1976. Higher feed costs change management programs in San

Diego County, California. Poult. Sci. 55:2007 (Abstract).

(3) Andersson, B., 1953. The'effect of injections of hypertonic NaCI solutions

into different parts of the hypothalamus of goats. Acta. Physiol.Scand. 28: 188-201.

(4) Box, G.E.P., and Jenkins, G.M., 1976. Time series analysis, forecasting

and control. Revised ed. Holden-Day, San Francisco, 575 p.I

(5) Ballard, P.D. and H.V. Biellier, 1969. The effect of photoperiod and

oviposition on feed and water consumption by chicken and laying hen_.Poult. Sci. 48: 1781-1782. (Abstract).

(6) Bonzer, B.J. and Plumart, P.E., 1976. A five year summary of egg produc-

tion feed costs and conversion. Poult. Sci. 55:2010 (Abstract).

(7) Davis, J.D., R.L. Gallagher and R. Ladove, 1967. Food intake controlled

by blood factor. Science, 156: 1247-1248.

(8) Draper, N.R. and It. Smith, 1966. Applied regression analysis. John wiley& Sons Inc., New York. 407 p.

(9) Hines, R.J. and J.F. Hurnik, 1977. The number and spacing of measurements

for the estimation of feed consumption. Poult. Sci., 56: 2101-2102.

(i0) Hughes, B.O., 1971. Allel0mimetic feeding in the domestic fowl. Br.Poult. Sci. 12: 359-366.

(ii) Hughes, B.O., 1972. A circadian rhythm of calcium intake in the domestic

fowl. Br. Poult. Sci., 13: 487-493.

(12) Hurnik, J.F., F.M. Jerome, B.S. Reinhart and J.D. Summers, 1971. Color

as a stimulus for feed consumption. Poult. Sci. 50: 944-949.

(13) Hurnik, J.F., D.J. Piggins, B.S. Reinhart and J.D. Summers, 1974. The

effect of visial pattern complexity of feeders on feed conuumption oflaying hens. Br. Poult. Sci. 15: 97-105.

(14) Hurnik, J.F., J.D. Summers, B.S. Reinhart and E.M. Swierczewska, 1977a.

Effect of age on the perfox_ance of laying hens during first yearof production. Poult. Sci. 56: 222-230.

(].5) Hurnik, J.F., J.D. Summers, J.P. Walker and W. Szkotnicki, 1977b. Pro-

duction traits influencing the individual feed conversion ratio.Poult. Sci. 56: 912-917.

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(16) Lee, C.Y., and A.W. Nordskog, 1975. Value of feed consumption records

to predict net income in layer-type chickens. Poult. Sci. 54:1912-1918.

(17) Lewis, N. and J.F. Hurnik and J.P. Walker, 1977. Stimulation of feeding

in neonatal turkey poults. Poult. Sci. 57: 1724-1725. (Abstract).

(18) Lindsted, K.J., 1971. Chemical control of feeding behaviour. Comp.

Biochem. Physiol. 39: 553-581.

(19) Mayer-Gross, W. and J. Walker, 1946. Taste and selection of food in

hypoglycemia. Br. J. Exp. Path., 27: 297-305.

(20) Nordskog, A.W., 1960. Importance of egg size and other factors in deter-

mining net income in random sample test. Poult. Sci. 39: 328-338.

(21) Nordskog, A.W., H. French and S.L. Balloun, 1969. Direct versus indirect

estimation of feed efficiency as a measure of performance. Poult. Sci.48: 1303-1310.

(22) Smith, M. and M. Dutty, 1957. Some physiological factors that regulate

eating behaviour. J. Comp. Physiol. Psychol., 50: 601-608.

(23) Valenstein, E.S., C.V. Cox and J.W. Kakolewski, 1968. Modification of

motivated behaviour elicited by electrical stimulation of they

hypothalamus. Science 159: 115-119.

(24) Weaver, W.C. and P.B. Siegel, 1968. Photoperiodicism as a factor in

feeding rhythms of broiler chickens. Poult. Sci. 47: 1148-1154.

(25) Wienzek, G., 1973. Messung des Pickimpulses bei Haush_hnern und K_ken

als quantitativer Verhaltens-Parameter. Forma et functio, 6:113-176.

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PROFIT ESTIMATES RELATED TO FEED CONVERSION

AND EGG PRODUCTION

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ECONOMIC PAI,_AMETERS RELATEDTO PERCENTILE

DISTRIBUTION (109_) OF FEED CONVERSION

INCOMEor i °/o PROFIT

COST $ i

15 .:.. 3s......... .,. Income - . -

_,q, •,Ibm, •

•. , '11'ql.4.•.

14 - " 25• -- . .

_2 :"_ '..

w

13 - '-. • • 15w_Qw

"._.. _• _.12: Cost _)_ 5

_" ..... - _ - : _"-_ 0

_ 'P .

11 - -5

!• .l

10 :_.• - -15

1 2 3 4 5 6 7 8 9 10

PERCENTILE ORDER

FJ.g. 4.

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Table i. Estimated efficiencies of varying number of feed

consumption measurements per hen

Interval

between

two

Number of observations Variancesratio

observations (weeks) (Efficiency)n k %

Twice a week 96 ... i00

Once a week 48 1 98.6

Every second week 24 2 i01.2 a

Every third week 16 3 98.8 a

Every fourth week 12 4 96.1a

Every sixth week 8 6 91.2 a

Every eighth week 8 8 85.6 a

Every twelfth week 4 12 76"9a

aNote: these efficiencies were calculated using the formula:

Cl2 .

Var _n,k ) = n-_ (n+2(n-l)pk + 2(n-2)P2 k + ... + p(n_l)k )

2where o = variance between hens, which is assumed to be constant overtime.

n = number of observations,

Ok= correlations between observations with lag k, 2k, etc.

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Table 2: Regression of l__n_ntransformed feed conversionratios

,i r - ,

A. Regression step__ R 2

1 Eggs .59

2 Eggs + Feed .75

3 Eggs + Feed + EG_._r .922

4 Eggs + Feed.+ EGWT + (eggs)2• 2 .985 Eggs + Feed + EG_ + (eggs) + (feed) .99

B. Regression parameters associated with R2 = .99 accuracy af estimates

, 2)Standard Relative contribution

Traits I) regr. coeff, to the estimate (%)

Eggs -0.829 35.9

Feed 0.670 28.9

EGWT -0. 414 18.0

(eggs) 2(feed)2 0.345 15.0-0.050 2.2

l)Eggs = Total egg production (no)

Feed = Total feed consumed (g)

EGWT = Average egg weight (g)

(eggs) 2

(feed) 2 = Squares of deviation from traint average.

2)Variation s •of the feed conversion'estimate considered as 100%.

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Table 3: Regression of feed conversion ratios onselected traits

A. Regression steps R2

1 Eggs .59

2 Eggs + (eggs) 2 .72

3 Eggs + (eggs) 2 + FBWT .75

4 Eggs + (eggs)2 + FBWT + EGWT .78

5 Eggs + (eggs) Z + FBWT + EG_ + IBWT .79

B. Regression parameters associated with R2 .79 accuracy of estimate '

Standard Relative Contribut ion 2)

Traits I) regr. coeff • to the estimate

s)2 0.404 27.8

FBWT 0.165 11.3

EG_._ .-0.222 15.2

IBWT 0.148 10.2

l)Eggs = Total egg production (no)

FB_ = Body weight at 71 wks of age (g)

EGWT = Average egg weight (g)

IB_ = Body weight at 23 wks of age (g)

(eggs) 2 = Square of deviation from average egg production

2)Variation of the feed conversion estimate considered as 100%.

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Appendix Table I. Estimated Variance Components and

lleritability coefficients for true

production and behavioural traits.

Variance ..

Components ±) Heritab ili ty

^2 ^2

: oF _ --(h2) S.E.(h 2)Production traits

Feed conversion (ratio) 0.0760 0.4461 .29 .103

Feed consumption (g) 39.12 79.27 .66 .112

Egg production (%) 0.00170 0.01387 .22 .099

Egg weight (g) 4.231 8.654 .66 ' .112

Egg mass (g) 9.167 52.010 .30 .103

Shell weight (g) 0.0577 0.1661 .52 .ii0

Deformation (_m) 4.947 12.772 .55 .iii

Egg composition:

Fresh yolk weight (g) 0.5216 0.8988 .73 .iii

Dry yolk weight (g) 0.1484 0.2459 .75 .Iii

Fresh albumen wt (g) 2.461 4.444 .71 .iii

Dry albumen wt (g) 0.0331 0.1461 .37 .i06

Behavioural observations: 2)

Eating 0.00118 0.00711 .28 .102

Drinking 0.00383 0.00547 .82 .II0

Standing 0.00357 0.00906 .54 .iii

Resting 0.00537 0.01558 .51 .Ii0

l)The analyzed sample consisted of 384 laying hens. The family structure was96 sires x 1 dam x 4 daughters.

2)Proportions of observed time, arcsln transformed.

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Appendix Table 2: Economic Figures used in calculation

Price of pullet $ 2.15/bird

Total fixed costs 2.55/bird/year

Labour .89/bird/year

Feed costs 165.00/ton

Price of eggs: Large .70/doz

Medium .62/dozSmall .45/doz

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