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Poult Sci 2007. 86:1615-1619
© 2007 Poultry Science Association
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ENVIRONMENT, WELL-BEING, AND BEHAVIOR

The Influence of Stocking Density on Body Weight, Egg Weight, and Feed Intake of Adult Broiler Breeder Hens

B. J. Mtileni*,1, K. A. Nephawe*, A. E. Nesamvuni{dagger} and K. Benyi{ddagger}

* Livestock Business Division, Agricultrual Research Council, Private Bag X2, Irene, 0062, South Africa; {dagger} Department of Agriculture, Private Bag X9487, Polokwane, 0700, South Africa; and {ddagger} University of Venda for Science and Technology, Private Bag X5050, Thohoyandou, 0950, South Africa

1 Corresponding author: jmtileni{at}arc.agric.za


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
The influence of stocking density on BW, egg weight (EW), and feed intake (FI) in Ross broiler breeder hens (n = 120) was investigated during the late medium egg production period (from 50 to 54 wk of age). Birds were randomly allocated to 6 pens in densities of 15, 20, and 25 birds/pen, giving rise to a floor space allowance of 5, 6.67, and 8.33 birds/m2, respectively. Each density was replicated twice, and the order among the 6 pens was chosen at random. Data were analyzed using the repeated measures techniques of the Statistical Analysis System, considering the covariance structure of the observed data. There was a significant effect attributable to stocking density, time (in days), and their interaction for BW, EW, and FI. Birds in density of 6.67 per m2 were lighter but had heavier eggs than birds in density of 5 per m2; however, birds in density of 8.33 per m2 had similar BW and EW with birds in the other 2 groups. The mean FI were statistically different among the 3 groups, with a reduction in FI as density increases. Total egg production within the 3 density groups and average egg production per bird were also analyzed using categorical data techniques. The results indicated that stocking density influenced egg production, with birds at higher density producing fewer eggs per bird. Although generous floor space allowances were allocated per bird in this experiment, stocking density influenced the performance of broiler breeder hens.

Key Words: broiler breeder • stocking density • body weight • feed intake • performance


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Social dominance in poultry describes the behavior of a bird that is allowed priority in access to food, mates, water, and nesting sites by others of its species because of its success in previous aggressive encounters. Less dominant birds frequently show subduing behavior toward a more dominant individual, to minimize evident aggression. In a stable flock of birds there may be a linear dominance hierarchy or pecking order (so called because it was first observed in the domestic fowl), with each bird showing subordination to those above it in the hierarchy and dominating those below (Hurnik et al., 1995).

Commercial poultry producers are often tempted to increase the number of breeding stock per pen as a method to reduce housing, equipment, and labor cost per pen. However, the literature indicates that high stocking densities can have a deleterious effect on the economics and welfare of poultry production. Hall (2001) observed a higher mortality, greater incidence of leg problems, and disturbed resting behavior in birds kept at high stocking densities. Chickens at high density grow more slowly, produce fewer eggs, and have higher mortality (Van Kampen, 1981; Deaton, 1983). Wells (1972) reported that feed consumption was significantly reduced among birds reared at high stocking density. On the other hand, eggs produced by birds kept at high stocking density were heavier than those produced by birds kept at low stocking density (Leeson and Summers, 1984; Carey, 1987).

The objective of this study was to evaluate the effect of stocking density on BW, egg weight (EW), feed intake (FI), and egg production (EP) in Ross-broiler breeder hens during the late medium EP period (from 50 to 54 wk of age).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Ross broiler breeder hens (n = 120) were randomly allocated to 6 floor pens measuring 2.5 x 1.2 m (3 m2), so that each pen contained 15, 20, and 25 hens. This gave rise to densities of 5, 6.67, and 8.33 birds/m2, respectively. The density level of 5 birds/m2 was used as control to represent the usual stocking density of 3.5 to 5.5 birds/ m2 (Ross Breeders Manual, 1998). Each density was replicated twice, and the order among the 6 pens was chosen at random. In each pen, birds were exposed to a fixed number of drinking and feeding troughs (1 bell drinker and 2 tube feeders), measuring 40 and 38 cm in diameter, respectively. A set of 12 nest boxes was provided per pen. These allocations were designed to be generously greater than the recommended allowances, and thus feeding, drinking and nesting space should inherently not depress performance.

An open-sided structure was used that had concrete floors covered with wood shavings. Pens were constructed of welded wires to allow birds in neighboring pens to have audio-visual contact as well as limited physical contact while feeding or drinking water from the troughs. The photoperiod was set to 16L:8D during the experimental period.

Birds were fed a predetermined limited quantity of feed based on their weekly EP rate to achieve the recommended commercial EP rate. At 0900 h, hens were offered feed at 140 g/bird of a commercial breeder diet, an amount above maintenance requirements during the experimental period.

The experiment was started from 50 to 54 wk of age after an adaptation period of 7 d. Daily FI was measured by the weigh-feeding-weigh method throughout the experimental period (before feeding and after feeding). Body weight, EW, and EP were also recorded per bird/day.

Statistical Analysis
In this experiment, birds were randomly allocated to pens representing different stocking densities, and multiple measurements of response (BW, EW, and FI) were taken on the same experimental units in a sequence of equally spaced points in time (in days). Data were analyzed using the repeated measures techniques of the Statistical Analysis System (SAS) in PROC MIXED (Littell et al., 1999). The following statistical model was used:


Formula

where yijk = measurement of response on the jth bird kept on ith density at kth time, µ = overall mean, di = effect of ith density on the measurements (i = 15, 20, 25), tk = effect of kth time on measurements (k = 1, 2, ..., 20), (dt)ik = interaction between ith density and kth time, {varepsilon}ij = random effect associated with the jth bird kept in ith density, eijk = random error associated with the jth bird kept in ith density at kth time.

The terms density, time, and density x time interaction were included in the model as fixed effects, whereas birds were considered as random effects. Basically there are 2 error terms, the between birds random error term ({varepsilon}ij) and the within birds random error term (eijk). In a repeated measures setup, 2 measurements taken at adjacent times are expected to be more highly correlated than 2 measurements taken several time points apart. Therefore, first order autoregressive correlation, AR(1), was used to model the covariance structure of the observed data (Littell et al., 1999).

Data were analyzed in 2 separate ways: 1) modeling time as a classification variable (the objectives are to compare stocking density trends over time to assess the possible interactions between stocking densities and time) and 2) modeling time as a regression variable. Regression variable was used because the variable time is quantitative, so as to model BW, EW, and FI as a polynomial function of time. This yields equations that can be used for comparing stocking density at specific times or predicting BW, EW, and FI for a stocking density at a specific time.

The number of eggs produced by each bird was counted to determine total EP for each density level. The categorical data techniques of SAS were used for the analysis of EP, and the average number of eggs per bird was determined for each density.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
The stocking density, time, and their interaction significantly (P < 0.05) influenced BW, EW, and FI of broiler breeder hens, when time was modeled as a classification or regression variable. The least square means (LSM) for different stocking densities for BW, EW, and FI when time was modeled as a classification variable are presented in Table 1Go. Birds kept in a group of 15 per pen were 183 g heavier than birds kept in groups of 20 per pen (P < 0.05). However, birds kept in a group of 25 birds per pen had similar BW to birds in the other 2 groups (P > 0.05). The results are in agreement with the literature reports of Leeson and Summers (1984); Keeling et al. (2003), and Estevez et al. (1997) that stocking density could affect BW in poultry. Leeson and Summers (1984) observed a significant reduction in 50-wk BW among birds kept at 293 cm2/bird compared with those kept at 586 cm2/bird. The effect of stocking density may be confounded with the effect of the group size. Keeling et al. (2003) maintained the stocking density at level 5 birds/m2 and observed that birds in the groups of 30 and 120 per pen were lighter than birds in groups of 15 and 60 per pen. They argued that hierarchical social structure based on individual recognition in small groups breaks down in large groups as birds become less aggressive and more tolerant. Thus birds attempt to form dominance relationships through aggression only up to a certain group size, above which they change strategy to become nonaggressive and more tolerant of each other (Estevez et al., 1997).


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  		Table 1. Least square means (LSM) and their SE for BW, egg weight, and feed intake at different stocking densities, modeling time as a classification variable
 
Birds kept in a group of 20 per pen produced eggs that were 1.38 g heavier (P < 0.05) than birds in a group of 15 per pen (Table 1Go). The mean EW of birds in the 25 group per pen was not different (P > 0.05) from the other 2 groups. Carey (1987) also found that eggs produced by birds reared at the high stocking density were heavier than those produced by birds at the low stocking density. The similar effect was also reported by Christmas et al. (1982) and Leeson and Summers (1984). Keeling et al. (2003) observed that eggs from birds in groups of 30 were significantly smaller than those from birds in the groups of 15, 60, and 120. Flemming (2005) indicated that bigger chicks hatch from bigger eggs hatch of a better quality with more residual yolk and low susceptibility to dehydration and heat loss. However, excessive increases in egg size, especially during late production, may have a negative effect on egg quality and egg handling because big eggs tend to have a poorer hatchability, poorer shell quality, and more cracks (Flemming, 2005). The associated effect of heavier EW on chick weight was not investigated in the current study.

The mean FI was different (P < 0.05) among the 3 groups, with a reduction in FI as density level increases (Table 1Go). Thus, greater stocking densities were associated with significantly lower feed consumption. This may be attributable to increased competition for feeding space. The results are in agreement with previous literature reports (Wells, 1972; Carey, 1987).

Figures 1Go, 2Go, and 3Go contain plots of the LSM for BW, EW, and FI at each stocking density over the several levels of time. Over time, the LSM for BW of birds kept in groups of 20 per pen was generally lower than for the other 2 groups (Figure 1Go). Although the effect of density on BW seemed parallel over time, it was not consistent throughout the experimental period. Noteworthy is that the LSM for EW and FI for different densities over time overlay at certain days but are clearly apart at other days (Figures 2Go and 3Go). The EW and FI might have been affected by crowding because with higher stocking density, there would be presumably more disturbances and less opportunity for individuals to feed. This concurred well with the ANOVA results that indicated significant interaction between stocking density and time for BW, EW, and FI.


Figure 1
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  		Figure 1. Least square means for BW at each stocking density over several levels of time.

 

Figure 2
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  		Figure 2. Least square means for egg weight at each stocking density over several levels of time.

 

Figure 3
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  		Figure 3. Least square means for feed intake at each stocking density over several levels of time.

 
Table 2Go presents parameter estimates (solutions) for the fixed effects of density and time on BW, EW, and FI and their SE, when time was modeled as a regression variable. Only the linear polynomials for the effect of time were included in the model in the final model because the quadratic effect was not significant (P > 0.05). The plots in Figures 1Go, 2Go, and 3Go also indicated that the linear equations should be adequate for regressions of BW, EW, and FI over time.


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  		Table 2. Parameter estimates for the fixed effects of density and time for BW, egg weight, and feed intake and their SE, modeling time as a regression variable
 
The parameter estimates were used to develop the prediction equation for BW, EW, and FI as follows:


Formula

The above equations might be used to predict BW, EW, and FI for birds kept at any of the 3 stocking densities at a particular day. For example, for a bird kept in a density of 20 per pen at d 10 during the peak of EP, its BW could be predicted as BW = 3,742.91 + (10.46 x 10) = 3,847.51 g. Egg weight and FI of broiler breeder hens kept in the studied stocking densities can also be predicted in the similar manner.

The total number of eggs and the average number of eggs per bird for each stocking density are presented in Figures 4Go and 5Go, respectively. The cumulative number of eggs was higher at a high-density environment than at a low-density environment, attributable to the confounding effect of density with group size. However, on a per bird basis, birds kept at a high-density environment produced fewer eggs than the low-density group. The average number of eggs per bird was 10.62, 9.96, and 9.40 for the 5, 6.67, and 8.33 birds/m2, respectively. Similar results have been reported by Ruggles et al. (1967), Ostrander and Young (1969), Van Kampen (1981, 1982), and Deaton (1983) that crowding has a depressing effect on EP per bird.


Figure 4
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  		Figure 4. Total number of eggs for each stocking density.

 

Figure 5
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  		Figure 5. Average number of eggs per bird for each stocking density.

 
Considering the results of this experiment, adequate bird density is an important concern for commercial broiler breeder hens. Broiler breeder growers rationalize that more profit may be realized from the enterprise by increasing the number of birds in a fixed pen. However, the results of this study suggest that the number of eggs per bird is reduced with increasing density levels. Furthermore, broiler breeder hens may produce heavier eggs at an intermediate density as compared with a higher density environment. However, the confounded effect of density with group size on EP rate and the impact of increased EW on chick survival may warrant future investigations.


   ACKNOWLEDGMENTS
 
The authors wish to thank A. Maiwashe, D. P. Visser, and S. F. Voordewind (Agricultural Research Council, Irene, South Africa) and A. Mamphiswana and W. Madzhuta (University of Venda, Thohoyandou, South Africa) for their help in this study. We also wish to acknowledge National Research foundation (NRF-project GUN no: 2050957) and Professional Development Programme (PDP) of the Agricultural Research Council for providing financial support.

Received for publication June 13, 2006. Accepted for publication April 5, 2007.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Carey, J. B. 1987. Effect of Pullet-Stocking Density on Performance of Laying Hens. Poult. Sci. 66:1283–1287.[ISI][Medline]

Christmas, R. B., C. R. Douglas, L. W. Kalck, and R. H. Harms. 1982. The effect of low protein pullet diet on performance of laying hens housed in the fall. Poult. Sci. 61:2103–2106.[ISI][Medline]

Deaton, J. W. 1983. Alleviation of heat stress for avian egg production—A review. World’s Poult. Sci. J. 39:210–217.[ISI]

Estevez, I., R. C. Newberry, and L. Arias de Reyna. 1997. Broiler chickens: A tolerant social system? Etologia 5:19–29.

Flemming, E. 2005. Controlling Late Egg Size. Aviagen. http://thepoultrysite.com/articles/366/controlling-late-egg-size Accessed Apr. 2006.

Hall, A. L. 2001. The effect of stocking density on the welfare and behaviour of broiler chickens reared commercially. Anim. Welf. 10:23–40.[Medline]

Hurnik, J. F., A. B. Webster, and P. B. Siegel. 1995. Dictionary of Farm Animal Behavior, 2nd ed. Iowa State Univ. Press, Ames, IA.

Keeling, L. J., I. Estevez, R. C. Newberry, and M. G. Correia. 2003. Production-related traits of layers in different sized flock: The concept of problematic intermediate group sizes 1. Poult. Sci. 82:1393–1396.[Abstract/Free Full Text]

Leeson, S., and J. D. Summers. 1984. Effect of cage density and diet energy concentration on the performance of growing leghorn pullets subjected to early induced maturity. Poult. Sci. 63:875–882.[ISI][Medline]

Littell, R. C., G. A. Milliken, W. W. Stroup, and R. D. Wolfinger. 1999. SAS System for Mixed Models. SAS Inst. Inc., Cary, NC.

Ostrander, C. E., and R. J. Young. 1969. Effect of density in cages on egg production, feed efficiency, egg size and economics. Poult. Sci. 48:1855. (Abstr.)

Ross Breeders Manual. 1998. Parent Stock Management Manual 308. Ross Breeders Ltd., Newbridge, Midlothian, UK.

Ruggles, L. H., D. L. Anderson, R. A. Damon, and R. M. Grover. 1967. The effects of bird density, light intensity and diet on the performance of heavy type layers in cages. Poult. Sci. 46:1313. (Abstr.)

Van Kampen, M. 1981. Thermal influences on poultry. Pages 131–147 in Environmental Aspects of Housing for Animal Production. J. A. Clark, ed. Butterworths, London, UK.

Van Kampen, M. 1982. Role of physiology in the tropics. Pages 240–256 in Animal Production in the Tropics. M. K. Yousef, ed. Praeger, New York, NY.

Wells, R. G. 1972. The effect of varying stocking density on the development and subsequent laying performance of floor-reared pullets. Poult. Sci. 13:13–25.





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