Effects of Population Density on Layer Performance1

Effects of Population Density on Layer Performance1 K. LEE and C. W. MOSS Department of Agriculture, University of Arkansas, Pine Bluff, Arkansas 71601 ABSTRACT Four experiments were conducted to study the effects of population density on layer performance. In each experiment, 20-wk-old White Leghorn pullets were housed in 30.5 x 50.8 cm cages at the rate of one, two, three, and four birds per cage for Treatments 1, 2, 3, and 4, respectively. In Experiment 4, there were three additional treatments: for Treatments 5,6, and 7, birds were placed into identical cages (30.5 x 50.8 cm) at the rate of three, two, and three birds per cage, respectively, at 20 wk of age. At 28 wk of age, one bird was removed from each cage in Treatment 5, and one bird was added to each cage in Treatments 6 and 7. In the first three experiments, all eggs that were collected for 2 consecutive d every 8 wk starting at 28 wk of age were used to measure egg traits. In Experiment 4, egg traits were determined once at 52 wk of age. Birds at the highest population density had the lowest percentage hen-day egg production and had one of the poorest feed efficiencies. Egg production was negatively correlated (P < .01, Experiments 1, 2, 3; P < .05, Experiment 4) with population density. Feed required to produce a dozen eggs was positively correlated (P <, .01, Experiments 1, 2; P < .05, Experiment 3) with population density in three out of the four experiments. The addition or removal of a cage mate to or from a multiple-bird cage in Experiment 4 did not (P > .05) affect egg production or feed efficiency. Final BW, mortality, and egg weight were not (P > .05) affected by population density. Only in one out of the four experiments was feed consumption (Experiment 1), eggshell thickness (Experiment 2), or albumen height (Experiment 3) lowered (P < .05) by having more than one bird per cage. This study showed that increasing population density decreased laying performance of the birds. (Key words: population density, egg production, feed efficiency, mortality, egg measurements) 1995 Poultry Science 74:1754-1760

INTRODUCTION

Floor space allowance per bird and group size per given space may affect layer performance and profitability. The magnitude of their influence may depend upon the housing type and bird placing practice. Lee (1989) reported that floor space allowance and group size did not seem to have an additive effect on production parameters in a floor pen environ-

Received for publication February 2, 1995. Accepted for publication June 16, 1995. Research supported by CSRS Evans-Allen PL 95-113, Section 1445, AR. X. 01351.

ment. However, in cage housing, Hill (1977) reported that floor space allowance and group size effects were independent and additive, the latter being more important in determining profitability. Increasing population density decreases floor space allowance and increases group size. Studies on the subject of population density effects on production parameters have shown conflicting results. Increasing population density has been reported to decrease egg production (Bramhall and Little, 1966; Rose and Sell, 1969; Mather and Gleaves, 1970; Cunningham, 1988), reduce feed efficiency (Roush et al, 1984; Adams and Craig, 1985), and increase mortality (Roush et al., 1984;

1754

POPULATION DENSITY AND LAYER PERFORMANCE

Sandoval et al, 1991). Other studies, however, indicated that increasing population density had no effect on egg production (Marks et al, 1970; Craig et al, 1986; Okpokho et al, 1987), feed efficiency (Marks et al, 1970; Quart and Adams, 1982; Okpokho et al, 1987), mortality (Bramhall and Little, 1966; Marks et al., 1970), egg weight, shell thickness, or Haugh units (Marks et al, 1970; Hill, 1977). The inconsistency of population density effects on feed consumption, egg production, and feed efficiency was noticed by Brake and Peebles (1992), who employed the same three density levels in two trials. Objectives of this study were to examine the effects of population density on BW, feed consumption, egg production, feed efficiency, egg characteristics, and pullet mortality. MATERIALS AND METHODS Four experiments were conducted with two commercial strains of White Leghorns. Hy-Line® W-36 pullets were used in Experiments 1, 2, and 4, and Shaver®288 birds were used in Experiment 3. In each experiment, 20-wk-old pullets were individually weighed, leg-banded, and randomly placed into 30.5 x 50.8 cm cages at the rate of one, two, three, and four birds per cage for Treatments 1, 2, 3, and 4, respectively. Because regrouping of birds occurs in the poultry industry, three additional treatments were included in Experiment 4 to examine whether early addition or removal of a bird to or from the cage would influence bird performance. In Treatments 5, 6, and 7, pullets were placed into identical cages (30.5 x 50.8 cm) at the rate of three, two, and three birds per cage, respectively, at 20 wk of age. At 28 wk of age, one bird was removed from each cage in Treatment 5, and one bird from like environments was added to each cage in Treatments 6 and 7. In all experiments, each treatment had six replicate cage sections, except for Experiment 4, in which each treatment had three replicate cage sections. There were six cages together in a replicate cage section in Experiments 1 and 2, whereas in Experiments 3 and 4, three cages were together in a replicate cage section.

1755

All data except for BW were collected on a replicate cage section basis. Final BW was measured individually at 52 wk of age and then averaged on a replicate cage section basis. Feed and water were consumed ad libitum for a period of 32 wk under a 16 h / d lighting regimen. Feed was weighed every 8 wk starting at 20 wk of age. Egg production and mortality were recorded daily. In the first three experiments, eggs were collected for 2 consecutive d every 8 wk starting at 28 wk of age and were used to measure egg weight, albumen height, and eggshell thickness. In Experiment 4, these measures were determined once at 52 wk of age. All data, except for mortality, were analyzed using ANOVA procedure of SAS/STAT® (SAS Institute, 1985) with means separated by Duncan's multiple range test at the 5% level of probability. Mortality data were analyzed using the chi-square test (Gill, 1978). Correlation coefficients between population density and layer performance were computed using SAS/STAT®. RESULTS AND DISCUSSION Birds at the highest density level (Treatment 4) had a lower (P < .05) percentage hen-day egg production than birds at the lowest density level (Treatment 1) in all experiments, except for Experiment 4, in which no differences were found among treatments (Tables 1 and 2). This is in general agreement with the findings of Hester and Wilson (1986), who reported that a decline in ovulation rate of birds in higher density treatments accounted for the decrease in hen-day egg production. Currently, most U.S. egg producers use relatively high population density (floor space range: 271 to 348 cm2 per bird per cage) as compared to that of European producers (approximate floor space range: 432 to 561 cm2 per bird per cage), according to Craig and Swanson (1994). North and Bell (1990) suggested a floor space allowance of 387 cm2 per bird for caged layers (standard Leghorn, 19 wk and older). In this study, birds in Treatment 4 had 387 cm2 of floor space allowance per bird, yet their laying performance was the poorest in the first three

1 2 3 4 SEM, pooled ANOVA summary Source of variation Population density

1,549 775 516 387

1,549 775 516 387

1 2 3 4

1 2 3 4

(cm2) 1,549 775 516 387

(no.) 1 2 3 4

1 2 3 4

SEM, pooled ANOVA summary Source of variation Population density 1 2 3 4 SEM, pooled ANOVA summary Source of variation Population density

Floor space/bird

Bird/ cage

Treatment

1,843 1,812 1,826 1,825 13

9

1,504 1,514 1,525 1,542

.1635 125.8 124.1 124.0 120.4 1.2

.4341

.1313

1.0

.0004 111.3 111.5 110.5 106.2

108.6" 103.2b 101.1'' 99.8b .9

— (g)

Feed/bird/d

.5405

.4085

1,449 1,489 1,461 1,498 11

BW (52 wk)

.

1.0

80. 78. 76.8 71.5

.

81. 76. 77. 69. 1.2

.

80. 78. 73. 69. 1.

(%

He pro

"-'Means within a column within each experiment with no common superscript differ significantly (P S .05). iHy-Line® W-36, Experiments 1 and 2; Shaver®-288, Experiment 3.

Experiment

TABLE 1. Effects of population density on final BW, laying performance, and mortality of b

iHy-Line® W-36.

1 2 3 4 5 6 7 SEM, pooled ANOVA summary Source of variation Population density

Treatment

(20 wk)

(no.)

Bird/cage

(28 wk) 1,549 775 516 387 516 775 516

(20 wk) (cm*) 1,549 775 516 387 775 516 387

(28 wk)

Floor space/bird .

.9905

15

1,398 1,406 1,361 1,397 1,371 1398 1,397

BW (52 wk)

(g)

.7070

102.4 109.7 107.3 1065 112.9 108.8 103.7 1.6 Pr

Feed/bird/d

TABLE 2. Effects of population density and addition or removal of a cage mate on fin and mortality of birds1 from 20 to 52 wk of age. Experiment

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LEE AND MOSS TABLE 3. Correlation coefficients between population density and layer1 performance from 20 to 52 wk of age Experiment

Variable correlated

1

2

Population density and hen-day egg production Population density and feed/doz eggs

-.867** .555"

-.723" .594"

3

4

-.655" .419*

-.449* .215

(r)

iHy-Line® W-36, Experiments 1, 2, and 4; Shaver®-288, Experiment 3. *P £ .05. " P S .01.

experiments. Although this study shows that percentage hen-day egg production is generally higher for birds in single-bird cages than birds in multiple-bird cages, placing only one bird per cage is obviously not economically advantageous when considering labor and equipment costs per cage. Feed and egg prices also influence profitability. Roush et al. (1984) reported that profitability associated with increased population density was sensitive to changes in those prices. Only in one (Experiment 1) out of the four experiments, did placing more than one bird per cage result in a reduction (P £ .05) in feed consumption per bird without affecting final BW (Tables 1 and 2). Carey (1990) reported that feed consumption of layers was not affected by cage population. In his study, however, floor space allowance per bird was held constant. Havenstein et al. (1989) reported that pullets housed at three per cage weighed less (P < .001) than those housed at four per cage at 35 wk of age. Feed efficiency was poorer (P ^ .05) for birds in Treatment 4 than for birds in Treatment 1 in Experiments 1 and 2 (Table 1). This was due to reduced egg production rates of birds in Treatment 4. In Experiment 3, feed efficiency for birds in Treatment 4 was the poorest (P > .05) among all groups. In Experiment 4, feed efficiency was not different among treatments (Table 2). Poorer feed efficiency due to increased population density was reported by Davami et al. (1987), whereas Cunningham and Ostrander (1982) observed the opposite. In this study, correlation coefficient analyses revealed that egg production was negatively correlated (P ^

.01, Experiments 1, 2? 3; P <, .05, Experiment 4) with population density (Table 3). Feed required to produce a dozen eggs was positively correlated (P < .01, Experiments 1, 2; P < .05, Experiment 3) with population density in three out of the four experiments. In analyzing 15 reports published between 1971 and 1983, Adams and Craig (1985) found a curvilinear relationship between population density and performance traits, such as egg production and feed efficiency, with more rapidly declining performance at higher densities. The addition or removal of a cage mate to or from a multiple-bird cage in Experiment 4 did not affect egg production or feed efficiency (Table 2). The results may indicate that this type of practice does not sufficiently alter the environmental or social pressure to affect layer performance. Previously, Hester and Wilson (1986) reported that introduction of unfamiliar birds to resident birds at specific times during the laying cycle did not influence egg production or feed efficiency. Mortality was unaffected by population density (Tables 1 and 2). This is in agreement with the findings of Davami et al. (1987), but not in agreement with Sandoval et al. (1991), who noticed higher mortality for birds in crowded cages. Four-period average egg weight (Experiments 1, 2, and 3) or 52-wk egg weight (Experiment 4) was not affected by population density (Tables 4 and 5). This is in agreement with the findings of Cunningham and Ostrander (1982). The addition or removal of a cage mate to or from a multiple-bird cage did not affect 52-wk egg weight in Experiment 4 (Table 5). Only in one out of the four experiments

1759

POPULATION DENSITY AND LAYER PERFORMANCE 1

TABLE 4. Effects of population density on average egg measurements Experiment2

Treatment 1 2 3 4 SEM, pooled ANOVA summary Source of variation Population density 1 2 3 4 SEM, pooled ANOVA summary Source of variation Population density 1 2 3 4 SEM, pooled ANOVA summary Source of variation Population density

Bird/cage

Floor space/bird

Egg weight

Albumen height

(no.) 1 2 3 4

(cm*) 1,549 775 516 387

(g) 54.6 55.5 56.0 56.3 .3

7.46 6.91 7.08 7.10 .09

1 2 3 4

1,549 775 516 387

59.6 58.8 59.4 57.8 .4

8.05 7.81 7.91 8.15 .07

1 2 3 4

1,549 775 516 387

.4461 57.9 55.4 56.0 56.5 .4

.2960 8.52" 7.92" 7.97b 7.88" .08

.0926

Shell thickness (mm) .358 .363 .365 .369 .002

.1424 .387" .374" .374b .364" .002

.1600

.0032 .405 .400 .399 .405 .001

— Probability • .2881 .0080

.1313

"•"Means within a column within each experiment with no common superscripts differ significantly (P 2 .05).

Average of four 56-d period measurements starting from 28 wk of age. Hy-Line® W-36 pullets were used in Experiments 1 and 2; Shaver®-288 pullets were used in Experiment 3.

2

TABLE 5. Effects of population density and addition or removal of a cage mate1 on 52-wk egg measurements, Experiment 4 Bird/cage Treatment 1 2 3 4 5 6 7

(20 wk) 1 2 3 4 3 2 3

SEM, pooled ANOVA summary Source of variation Population density

iHy-Line® W-36.

(28 wk)

— (no.) 1 2 3 4 2 3 4

Floor space/bird (20 wk) 1,549 775 516 387 516 775 516

(28 wk) (cm2) 1,549 775 516 387 775 516 387

Egg weight

Albumen height

(g) 55.2 54.2 53.4 54.4 53.4 53.3 53.1

7.80 7.50 7.45 7.21 7.28 7.50 7.12

(mm) .397 .396 .395 .390 .397 .392 .399

.4

.09

.002

.8029

Shell thickness

— Probability .4440 .9609

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LEE AND MOSS

was eggshell thickness (Experiment 2) or albumen height (Experiment 3) lowered (P < .05) by having more than one bird per cage (Tables 4 and 5). Results of this study showed that increasing population density resulted in decreased laying performance of the birds under the conditions of this study. REFERENCES Adams, A. W., and J. V. Craig, 1985. Effects of crowding and cage shape on productivity and profitability of caged layers: A survey. Poultry Sri. 64:238-242. Brake, J. D., and E. D. Peebles, 1992. Laying hen performance as affected by diet and caging density. Poultry Sci. 71:945-950. Bramhall, E. L., and T. A. Little, 1966. Layer performance as affected by debeaking method and cage density. Poultry Sci. 45:1072.(Abstr.) Carey, J. B., 1990. The influence of cage population on the productive performance of three strains of layers. Poultry Sci. 69(Suppl. l):30.(Abstr.) Craig, J. V., and J. C. Swanson, 1994. Review: Welfare perspectives on hens kept for egg production. Poultry Sci. 73:921-938. Craig, J. V., J. Vargas, and G. A. Milliken, 1986. Fearful and associated responses of White Leghorn hens: Effects of cage environments and genetic stocks. Poultry Sci. 65:2199-2207. Cunningham, D. L., 1988. Effects of population size and cage area on agonistic activity and social structure of White Leghorn layers. Poultry Sci. 67:198-204. Cunningham, D. L., and C. E. Ostrander, 1982. The effects of strain and cage shape and density on performance and fearfulness of White Leghorn layers. Poultry Sci. 61:239-243. Davami, A., M. J. Wineland, W. T. Jones, R. L. Ilardi, and R. A. Peterson, 1987. Effects of population size, floor space, and feeder space upon productive performance, external appearance, and plasma corticosterone concentration of laying hens. Poultry Sci. 66:251-257. Gill, J. L., 1978. Design and Analysis of Experiments in the Animal and Medical Sciences. Vol. 1. Iowa State University Press, Ames, IA.

Havenstein, G. B., V. D. Toelle, R. H. Towner, and A. Emsley, 1989. Effects ofy genetic strain, slow versus rapid-feathering maternal genotype, and cage density on the performance of Single Comb White Leghorns. Poultry Sci. 68:596-607. Hester, P. Y., and E. K. Wilson, 1986. Performance of White Leghorn hens in response to cage density and introduction of cage mates. Poultry Sci. 65: 2029-2033. Hill, A. T., 1977. The effects of space allowance and group size on egg production traits and profitability. Br. Poult. Sci. 18:483-492. Lee, K., 1989. Laying performance and fear response of White Leghorns as influenced by floor space allowance and group size. Poultry Sci. 68: 1332-1336. Marks, H. L., L. D. Tindell, and R. H. Lowe, 1970. Performance of egg production stocks under three cage densities. Poultry Sci. 49:1094-1100. Mather, F. B., and E. W. Gleaves, 1970. Performance of commercial stocks of layers as influenced by cage density. Poultry Sci. 49:1412.(Abstr.) North, M. O., and D. D. Bell, 1990. Commercial Chicken Production Manual. 4th ed. Van Nostrand Reinhold, New York, NY. Okpokho, N. A., J. V. Craig, and G. A. MilUken, 1987. Density and group size effects on caged hens of two genetic stocks differing in escape and avoidance behavior. Poultry Sci. 66:1905-1910. Quart, M. D., and A. W. Adams, 1982. Effects of cage design and bird density on layers. 1. Productivity, feathering, and nervousness. Poultry Sci. 61:1606-1613. Rose, R. J., and J. L. Sell, 1969. Comparison of rearing and laying house programs with regard to pullet performance. Poultry Sci. 48:1863.(Abstr.) Roush, W. B., M. M. Mashaly, and H. B. Graves, 1984. Effects of increased bird population in a fixed cage area on production and economic responses of Single Comb White Leghorn laying hens. Poultry Sci. 63:45-48. Sandoval, M., R. D. Miles, and R. D. Jacobs, 1991. Cage density and house temperature gradient effects on performance of White Leghorn hens. Poultry Sci. 70(Suppl. l):103.(Abstr.) SAS Institute, 1985. SAS/STAT® Guide for Personal Computers. Version 6 Edition. SAS Institute Inc., Cary, NC.