J. Appl. Poult. Res.
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J APPL POULT RES 2008. 17:505-514. doi:10.3382/japr.2008-00062
© 2008 Poultry Science Association
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Research Reports

Effect of Initial Full Feeding of Broiler Breeder Pullets on Carcass Development and Body Weight Variation

A. Pishnamazi*, R. A. Renema*,1, M. J. Zuidhof{dagger} and F. E. Robinson*

* Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5, Canada; and{dagger} Agriculture Research Division, Alberta Agriculture and Rural Development, Edmonton, Alberta T6H 5T6, Canada

1 Corresponding author: robert.renema{at}ualberta.ca


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Broiler breeder pullets are fully fed for several weeks to give chicks a vigorous start, to establish an adequate frame size, and to build increased flock BW uniformity. This study was designed to determine whether reducing the length of the initial ad libitum feeding period of pullets would be detrimental to subsequent fleshing, skeletal development, and BW variation. A total of 720 Ross 308 pullets were placed in 8 pens on the day of hatch and provided ad libitum access to feed at 1 wk (1WK) or 3 wk (3WK) of age, at which time a 5:2 restriction program began. Individual BW and external fleshing scores, and flock BW variation (CV and uniformity) were monitored. At 4, 8, 12, and 16 wk, 60 randomly selected birds per treatment were dissected for assessment of breast muscle, fatness, and reproductive development. At 3 wk of age, BW of the 3WK pullets (471 g) was greater than that of the 1WK pullets (312 g), and the daily rate of gain was double. Although feed allocation was decreased markedly at 3 wk in 3WK birds, by 4 wk they weighed 30% more, and had a greater frame size and proportion of breast muscle than the 1WK birds. At 8 wk of age, the 3WK birds were still heavier (973 g for 3WK vs. 899 g for 1WK). Most carcass measures were similar between treatments at 12 wk of age, by which time BW profiles were similar. At 16 wk of age, frame size and proportion of breast muscle were not different between groups. The BW variation did not differ through the initial 12 wk, but was superior at 14 and 16 wk of age in 1WK birds, possibly because of greater feed allocation between 8 to 16 wk, which is the most intense feed restriction period. The reduced feed intake of 3WK birds at the onset of feed restriction reduced their ME requirement for maintenance, likely contributing to this result. Increasing the length of the ad libitum feed access period after hatch altered growth and conformation traits to 8 wk of age and did not affect frame size or proportion of breast muscle, but increased BW variability late in the rearing period.

Key Words: broiler breeder • feed restriction • frame size • maintenance energy • flock uniformity


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
The increase in broiler performance has been tremendous in recent years, as measured by growth rate, feed conversion, and carcass yield. There is a negative relationship between increased BW caused by overfeeding and reproductive efficiency in broiler breeders [1]. In general, broiler breeders that are overweight show poor egg production, fertility, and hatchability; an increased likelihood of producing eggs with shell defects or multiple yolks; more than 1 egg laid per day; and a high incidence of eggs laid out of the usual 6- to 8-h period of lay [2, 3]. Broiler breeders are feed restricted to limit growth rate and these associated problems.

Feeding level and feeding patterns during the rearing period can affect sexual maturation and have lasting effects on growth and production traits [4, 5]. Wilson et al. [6] reported that beginning a feed restriction program for breeder pullets as early as 2 wk of age was equivalent to or better than initiation at 4 wk of age or later. The timing and magnitude of breast muscle, abdominal fatpad, and reproductive tract growth have been associated with both feeding level and rate of lay [4, 5, 7–10]. The genetics of broilers has changed greatly since many of these studies were conducted. Increased growth potential requires more severe feed restriction to control BW in broiler breeder pullets [11].

The time period varies in which commercial broiler breeder pullets are given full access to feed early in the pullet-rearing phase. With recommendations for minimum frame sizes and strong early starts, there is the potential for overshooting early BW targets and the need for a sudden change to restricted feeding conditions. When feed allocation is too high early in rearing (21 d), pullets can become overweight. By 28 to 35 d of age, feed increments must have been reduced to prevent birds from becoming too heavy. In commercial practice, managers tend to overcorrect feed allocations when trying to draw deviant BW closer to the target. Slow early growth has been a concern if frame size is also limited because small-framed pullets may gain excessive breast muscle mass even when maintained on a normal target BW profile. The purpose of this study was to determine the effect of an initial 1- or 3-wk ad libitum broiler breeder pullet feeding period on subsequent fleshing and frame size development, and on flock BW uniformity.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
The birds studied in this project were managed according to the Guide to the Care and Use of Experimental Animals [12]. The experimental protocol was approved by the Livestock Animal Care and Use Committee of the University of Alberta.

Stock and Management
At hatch, 720 Ross 308 breeder pullets were randomly allocated to 8 floor pens (90/pen) and were provided ad libitum access to feed to 1 (1WK) or 3 wk (3WK) of age. After the ad libitum period, a 5:2 feed restriction program was used (birds were fed 5 d/wk, interspersed with 2 nonfeed days). Target BW profiles converged at 10 wk of age. Group BW of each pen of pullets were obtained twice per week (on the nonfeed days) and mean BW of the group was used to determine the feed allocation needed to achieve the target BW for the next period. Feed was provided in mash form with 19% CP and 2,900 kcal of ME/kg of starter feed (0 to 21 d of age) and 16.7% CP and 2,900 kcal of ME/kg of grower diet (22 to 112 d of age), following breeder recommendations. Water was available ad libitum. The lighting program consisted of 24 h of light for the first 3 d, followed by a reduction to 8 h of light per day, which was maintained for the duration of the study.

Parameters Measured
Feed intake during the ad libitum phase of the study was recorded weekly on a pen basis and daily once feed restriction began. Individual BW data were recorded between 0600 and 0800 h: weekly from 0 to 4 wk, and every other week thereafter. Variation in BW was measured in each pen through calculation of the CV of BW and the ±15% uniformity. Shank (from the bottom of the footpad to the top of the hock joint) and keel length (from the hypocleidoclavical joint to the caudal end of the sternum) was recorded every 4 wk, and chest width and girth measurements were recorded on all birds at 8, 12, and 16 wk. Shank and keel lengths were recorded by using digital calipers, as an estimate of frame size. Chest width was measured with calipers placed under the wings, 2.5 cm below the clavicle bones at the widest point on the chest. Chest girth was the distance around the thoracic cavity, determined by using a fabric tape measure with the notch of the keel as a reference point, as described by Griffin et al. [13]. At 4, 8, 12, and 16 wk, 60 birds/treatment that had been randomly selected at placement (15/ pen) were processed to determine pectoralis major and pectoralis minor weights. Breast muscle weight was calculated as their combined weight. The liver and abdominal fatpad were weighed at each processing age. The abdominal fatpad included fat adhering to the gizzard and cloaca. Ovary weight was determined at 12 and 16 wk. When birds were removed from the pens, feeder space was reduced to ensure that age-specific recommendations for pullet feeder space were maintained.

Estimation of Energy Requirements
Daily ME requirements for maintenance were estimated weekly to 4 wk and every other week thereafter by using a linear energetics model:


Formula

where MEIit was the ME intake (kcal/d) for each treatment i during time t (wk); BWit was the estimated BW (kg) for treatment i during time t, calculated as (BWt + BWt-1)/2; ADGt was the average daily gain (g) during time t; β1 was the estimated ME requirement for BW gain, estimated as a constant across treatments and time; and β0it was the estimated energy requirement for maintenance for each treatment i at time t.

Statistical Analysis
Data were analyzed as a 1-way ANOVA, with feeding regimens (1WK or 3WK) as the main effect [14]. Data for each age were analyzed independently by using the MIXED procedure of SAS [14]. Pairwise differences between means were determined with the PDIFF option of the LSMEANS statement [14]. Metabolizable energy requirements were estimated by using the MIXED procedure of SAS, with average daily gain and the interaction effect of age x treatment x BW0.75 as sources of variation. Regression analysis was conducted by using the REG procedure of SAS. All statements of significance were based on P ≤ 0.05.


   RESULTS AND DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Feed Consumption and Growth
Feed consumption was similar in the 1WK and 3WK pullet groups to 2 wk of age (Figure 1Go). Despite feed restriction beginning at 7 d in the 1WK group, birds did not consume all their feed until 10 d of age, when feed restriction effectively started. At 2 wk of age, the 3WK birds weighed more (204.7 g) than the 1WK birds (181.4 g; Figure 2Go). By 3 wk, the difference in BW had increased to 157 g, a 51% greater BW in 3WK than in 1WK birds. During the third week, the 3WK birds consumed 2.05 times the feed consumed by the 1WK birds (Figure 1Go), equating to a CP intake of 85.8 vs. 41.9 g, and an ME intake of 1,310 vs. 640 kcal in 3WK vs. 1WK pullets, respectively.


Figure 1
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  		Figure 1. Feed intake profiles for broiler breeder pullets from 1 to 16 wk of age after a 1-wk (1WK) or 3-wk (3WK) initial full feeding period. Feed allocation subsequent to the full feeding phase was designed to meet target BW gains determined twice per week.

 

Figure 2
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  		Figure 2. Body weight profiles for 2 feeding programs for broiler breeder pullets from 0 to 16 wk of age after a 1-wk (1WK) or 3-wk (3WK) initial full feeding period.

 
At 3 wk of age, feed allocation to the 1WK birds increased by 7.3 g/bird (23%) to maintain the target BW profile, whereas the 3WK birds received a 23.1 g/bird (36%) reduction in feed allocation because actual BW were greater than the target BW (Figure 1Go). It is clear that to avoid having to reduce the feed allocation, transition from ad libitum to restricted access to feed must begin before 3 wk of age. Without adequate monitoring of BW, Ross 308 pullets can be well above the target BW before the traditional 3 wk age at transfer to feed restriction suggested for this strain.

Although the BW of the 2 treatments were converging between 4 and 8 wk of age, the 3WK birds remained heavier than pullets on the 1WK treatment (Figure 2Go) despite the greater feed allocation to 1WK birds, surpassing that of the 3 WK birds (Figure 1Go). The 1WK birds consumed 3.2 g/bird per day more than 3WK birds at 8 wk of age. The relationship between energy intake and BW gain is very strong in feed restricted broiler breeder pullets [15].

Between 0 and 16 wk, pullets on the 3WK treatment consumed 5,156 g of feed: 877.4 g of protein, and 14.9 Mcal of ME. Similarly, the 1WK pullets consumed 5,153 g of feed: 871.3 g of protein, and 14.9 Mcal of ME. The 1WK birds consumed less starter feed than the 3WK birds by 3 wk of age, but made up for this shortfall with increased grower feed intake during the 8- to 14-wk period (Figure 1Go). Presumably, the sudden decrease in feed allocation for 3WK birds caused them to become more efficient in the short term, a process that was possibly supported through the use of additional stored energy present at the onset of restriction to sustain growth. These larger birds required less feed than was being allocated to 1WK birds to grow a comparable or slightly reduced amount (Figures 1Go and 2Go). However, providing a reduced feed allocation to 3WK birds compared with 1WK birds during the time when birds are most feed restricted (8 to 16 wk of age) could increase feed competition and have a negative effect on flock BW uniformity.

Energy Requirements
The ME requirement for gain, estimated across treatments and time, was 0.71 kcal/g (P = 0.036). The estimated ME requirement for maintenance (MEm) varied dramatically as a function of time (Figure 3Go), and was proportional to feed intake. Regression analysis confirmed a very strong relationship between MEm and feed intake per unit of BW0.75 for both the 1WK and the 3WK treatments (R2 = 0.994 and 0.996, respectively, P < 0.0001). At 3 wk of age, the ad libitum fed birds (3WK) had a much greater estimated MEm. From 4 to 12 wk, the 3WK birds had a lower feed allocation than the 1WK birds, which reduced the estimated MEm. Despite having a feed intake similar to the 1WK birds (Figure 1Go), during this period the heavier 3WK birds were consuming less feed per unit of BW to achieve the same growth rate because of a reduced MEm (Figure 3Go). These differences in MEm provide evidence that decreased feed intake had a direct negative effect on metabolic rate, and explains why there was no overall difference in efficiency.


Figure 3
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  		Figure 3. Calculated maintenance energy (MEm) requirements for broiler breeder pullets from 1 to 16 wk of age after a 1-wk (1WK) or 3-wk (3WK) initial full feeding period.

 
Gabarrou et al. [16] reported that less efficient hens demonstrate a greater thermogenesis, resulting in dissipation of excess energy as heat, explaining some of the variability in maintenance requirements attributable to feeding activity. Together, the liver, gut, and reproductive tract of broiler breeders represent 26 and 30% of the total energy expenditure in fed and fasted hens, respectively [17]. Differences in size and metabolic rate of these organs can have a considerable effect on maintenance requirements. Fasting increases liver tissue metabolism in broiler breeders, indicating the major role that liver plays in energy metabolism in fasted hens. In a comparison of divergently selected high and low residual feed intake lines, Gabarrou et al. [16] reported that although basal metabolic rate was similar between these groups, there were differences in feeding activity and regulatory thermogenesis. The altered MEm in the current study is part of the group of main sources of variability in residual feed intake summarized by Luiting [18]. The list includes physical activity, feather density, basal metabolic rate, area of bare skin, body temperature, and body composition.

BW Uniformity
From 0 to 12 wk, BW uniformity did not differ between treatments (Figure 4Go). At 14 and 16 wk of age, BW variation in birds in the 1WK treatment was less than that of birds in the 3WK treatment. The spread in results was the greatest at 16 wk of age, where the measures of CV of BW (P = 0.05; Figure 4Go) and ±15% uniformity (P = 0.01; 1WK = 78.7%, 3WK = 64.5%) indicated similar results. Based on how these measures of BW variation are calculated, their results are not always similar.


Figure 4
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  		Figure 4. Coefficient of variation of BW for broiler breeder pullets from 0 to 16 wk of age after a 1-wk (1WK) or 3-wk (3WK) initial full feeding period.

 
It is postulated that decreased feed allocation from 6 wk to control the BW of 3WK birds may have impaired BW uniformity. de Beer and Coon [19] reported that using skip-a-day compared with everyday feeding programs during periods of severe feed restriction improved flock uniformity. Plasma corticosterone concentrations were elevated in feed restricted compared with fully fed broiler breeder pullets between 6 and 18 wk of age [20]. Similarly, plasma heterophyl:lymphocyte ratios at 12 wk of age were reduced in pullets fed a diet diluted with 15 or 30% oat hulls, indicating that feed restriction-related stress may be reduced through increased feed volume [21]. Diet dilution allowed for larger feed intakes, presumably resulting in more equitable feed distribution among individuals, and was associated with improved BW uniformity during both the rearing and laying periods [21]. From approximately 14 wk of age, overfeeding caused excess growth and earlier sexual maturation. As a result, breeder females could become more heavily muscled and produce excess ovarian follicles, resulting in poor reproduction performance [22]. A flock with a highly uniform BW helps to harmonize the onset of sexual maturity, creates good peaks, and enables producers to meet the nutrient requirements of the flock more accurately, because one level of management optimizes the reproduction effect of a large proportion of birds.

Further consideration for an initial period of full feeding may be influenced by initial chick weight, quality, and brooding conditions. The CV for initial chick BW in this study was 7 (Figure 4Go), which is comparable with that reported previously [23].

Frame Size
At 4 and 8 wk of age, shank length and keel length were shorter in the 1WK group than in the 3WK group (Table 1Go). At 8 wk of age, chest girth was less in the 1WK than in the 3WK birds. Chest width was greater in 3WK fully fed pullets at 12 wk only. However, there were no differences in shank length, keel length, and chest girth at 12 or 16 wk of age. The heavier breast muscle weight of 3WK birds may have contributed to the larger chest girth (Table 1Go). These results agree with those of de Beer and Coon [19], who found that shank and keel length were greater in birds fed every day compared with birds fed on a skip-a-day regimen. In the current study, differences in frame size before 12 wk of age can be explained by differences in BW. Other research has shown that feed restriction programs limit keel length in a fashion similar to shank length [24]. This demonstrates that there were no differences in stunting to 16 wk of age caused by the initial full feeding treatments.


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  		Table 1. External carcass measurements, breast muscle, abdominal fatpad, and liver weights of broiler breeder pullets at 4, 8, 12, or 16 wk of age after a 1- or 3-wk initial full feeding period
 
Carcass Composition
The 1WK birds had less breast muscle at 4 and 8 wk (Table 1Go). However, there were no differences in breast muscle weight between treatments at 12 and 16 wk. Changes in breast muscle weight followed a pattern similar to changes in BW, which concurs with previous research [25]. The CP intakes for 3WK birds during the 0- to 3-wk and 4- to 8-wk periods were 135.5 and 265.4 g/bird, respectively, whereas 1WK birds consumed 89.4 and 264.5 g of CP/bird during these periods. Yaissle and Lilburn [26] reported that broiler breeder pullets fed low levels of protein had less breast muscle at 5 wk. Greater CP intake early in the pullet growth period has been reported to directly affect BW, breast weight, and shank and keel length at 6 wk of age, although this effect disappears after subsequently providing equivalent nutrient allocations [27]. This may indicate increased growth potential, particularly of breast muscle tissue in current, high-breast-yielding strains.

The abdominal fatpad weight was greater for 3WK pullets compared with 1WK pullets at 4 wk (Table 1Go). At 16 wk, 3WK birds also had heavier abdominal fatpads, whereas these birds had reduced BW. Consequently, the percentage of abdominal fat was different only at 16 wk, when 1WK birds had less fat than 3WK pullets. However, these data are based on very low fatpad weights, which are likely presenting predominantly dense connective tissue supporting structures rather than the fat itself. Normally, surplus nutrients in overfed birds result in an increased abdominal fatpad [28]. Robinson et al. [24] found a 4-fold difference in relative fatpad weight in birds with low vs. standard or high BW between 18 and 24 wk of age. They suggested that this change was due to a large increase in feed allocation for those birds during that period.

Pullets reared on the 1WK feed restriction program had significantly decreased liver weight at 4 wk of age compared with birds reared on the 3WK feed restriction program (Table 1Go). A large nutrient supply in broiler breeder pullets is associated with an excessive accumulation of lipid in the liver [1]. Yu et al. [4] found that feed restriction (37.2% of ad libitum intake) during rearing (4 to 18 wk) resulted in decreased liver weight (absolute and relative). Liver weight as a percentage was greater for 1WK birds at 4, 8, and 16 wk (Table 1Go). It seems that the greater liver weight as a percentage of BW of 1 WK birds is due to the decreased BW of these birds compared with 3WK birds at 4 and 8 wk of age (Figure 2Go). It would appear that the 1WK birds that were "catching up" in BW because of a more generous feed allowance after 8 wk of age may have been depositing excess dietary energy as stored lipid in the liver. Energy intake for 1WK birds for 8 to 16 wk was 9.0 Mcal of ME compared with 8.3 Mcal of ME for 3WK birds. de Beer and Coon [19] showed that consumption of large amounts of feed increases hepatic lipogenesis and possibly the deposition of more fat in the carcass.

Reproductive Organ Development
There were no significant differences in ovary weight as a consequence of the feeding treatments (data not shown). Even at 16 wk, mean ovary weight was less than 0.5 g. Ovary weight can be very responsive to feed allocation and influenced by BW profile [24]; however, the current study ended before we were able to make this determination.


   CONCLUSIONS AND APPLICATIONS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
REFERENCES AND NOTES
 

  1. Varying the duration of early ad libitum feed access altered growth and conformation traits to 8 wk of age, with no long-term effect on frame size or proportion of breast muscle.
  2. Reduced feed intake through feed restriction reduced the ME requirement for maintenance. Despite temporal differences in feed intake, there was no overall difference in frame size or breast muscle weight at 16 wk.
  3. Birds fully fed for 1 wk had better BW uniformity, beginning at 14 wk of age.
  4. Initial duration of full feeding did not affect reproductive development to 16 wk of age.


   ACKNOWLEDGMENTS
 
This study was supported by funds provided by the Alberta Agricultural Research Institute, the Canadian Poultry Research Centre, and Aviagen North America. Thanks to F. Dennis and the staff and students of the University of Alberta Poultry Research Centre for technical expertise.


   REFERENCES AND NOTES
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 

  1. Renema, R. A., and F. E. Robinson. 2004. Defining normal: Comparison of feed restriction and full feeding of female broiler breeders. Worlds Poult. Sci. J. 60:508–522.[CrossRef][Web of Science]
  2. Hocking, P. M. 1993. Effects of body weight at sexual maturity and the degree and age of restriction during rearing on the ovarian follicular hierarchy of broiler breeder females. Br. Poult. Sci. 34:793–801.[CrossRef][Web of Science][Medline]
  3. Bruggeman, V., O. Onagbesan, E. D’Hondt, N. Buys, M. Safi, D. Vanmontfort, L. Berghman, F. Vandesande, and E. Decuypere. 1999. Effect of timing and duration of feed restriction during rearing on reproductive characteristics in broiler breeder females. Poult. Sci. 78:1424–1434.[Abstract/Free Full Text]
  4. Yu, M. W., F. E. Robinson, and A. R. Robblee. 1992. Effect of feed allowance during rearing and breeding on female broiler breeders. 1. Growth and carcass characteristics. Poult. Sci. 71:1739–1749.[Web of Science][Medline]
  5. Yu, M. W., F. E. Robinson, R. G. Charles, and R. Weingardt. 1992. Effect of feed allowance during rearing and breeding on female broiler breeders. 2. Ovarian morphology and reproduction. Poult. Sci. 71:1750–1761.[Web of Science][Medline]
  6. Wilson, H. R., D. R. Ingram, F. B. Mather, and R. H. Harms. 1989. Effect of daily restriction and age at initiation of a skip-a-day program for young broiler breeders. Poult. Sci. 68:1442–1446.[Web of Science][Medline]
  7. Katanbaf, M. N., E. A. Dunnington, and P. B. Siegel. 1989. Restricted feeding in early and late-feathering chickens. 2. Reproductive responses. Poult. Sci. 68:352–358.[Web of Science][Medline]
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  9. Fattori, T. R., H. R. Wilson, R. H. Harms, and R. D. Miles. 1991. Response of broiler breeder females to feed restriction below recommended levels. 1. Growth and reproduction performance. Poult. Sci. 70:26–36.[Web of Science][Medline]
  10. Tolkamp, B. J., V. Sandilands, and I. Kyriazakis. 2005. Effect of qualitative feed restriction during rearing on the performance of broiler breeders during rearing and lay. Poult. Sci. 84:1286–1293.[Abstract/Free Full Text]
  11. Renema, R. A., F. E. Robinson, and M. E. Rustad. 2007. Implications of changes to commercial broiler and broiler breeder body weight targets over the past 30 years. Worlds Poult. Sci. J. 63:457–472.[Web of Science]
  12. Canadian Council on Animal Care. 1984. Guide to the Care and Use of Experimental Animals. Vol 2. Can. Counc. Anim. Care, Ottawa, Ontario, Canada.
  13. Griffin, A. M., R. A. Renema, F. E. Robinson, and M. J. Zuidhof. 2005. The influence of rearing light period and the use of broiler or broiler breeder diets on 42-day body weight, fleshing and flock uniformity in broiler stocks. J. Appl. Poult. Res. 14:204–216.[Abstract/Free Full Text]
  14. SAS Institute. 2002. SAS Version 9.1. SAS Inst. Inc., Cary, NC.
  15. Lilburn, M. S., K. Ngiam-Rilling, and J. H. Smith. 1987. Relationships between dietary protein, dietary energy, rearing environment, and nutritional utilization by broiler breeder pullets. Poult. Sci. 66:1111–1118.[Web of Science][Medline]
  16. Gabarrou, J. F., P. A. Geraert, N. Francois, S. Guillaumin, M. Picard, and A. Bordas. 1998. Energy balance of laying hens selected on residual food consumption. Br. Poult. Sci. 39:79–89.[CrossRef][Web of Science][Medline]
  17. Spratt, R. S., B. W. McBride, H. S. Bayley, and S. Leeson. 1990. Energy metabolism of broiler breeder hens. 2. Contribution of tissues to total heat production in fed and fasted hens. Poult. Sci. 69:1348–1356.[Web of Science][Medline]
  18. Luiting, P. 1990. Genetic variation on energy partitioning in laying hens: Causes of variation in residual feed consumption. Worlds Poult. Sci. J. 46:133–148.[CrossRef][Web of Science]
  19. de Beer, M., and C. N. Coon. 2007. The effect of different feed restriction programs on reproductive performance, efficiency, frame size, and uniformity in broiler breeder hens. Poult. Sci. 86:1927–1939.[Abstract/Free Full Text]
  20. Hocking, P. M. 1996. Role of body weight and food intake after photostimulation on ovarian function at first egg in broiler breeder females. Br. Poult. Sci. 37:841–851.[CrossRef][Web of Science][Medline]
  21. Zuidhof, M. J., F. E. Robinson, J. J. R. Feddes, R. T. Hardin, J. L. Wilson, R. I. McKay, and M. Newcombe. 1995. The effects of nutrient dilution on the well-being and performance of female broiler breeders. Poult. Sci. 74:441–456.[Web of Science][Medline]
  22. Renema, R. A., F. E. Robinson, M. Newcombe, and R. I. McKay. 1999. Effect of body weight and feed allocation during sexual maturation in broiler breeder hens. 1. Growth and carcass characteristics. Poult. Sci. 78:619–628.[Abstract/Free Full Text]
  23. Wolanski, N. J., F. E. Robinson, R. A. Renema, V. L. Carney, and B. I. Fancher. 2007. Relationships among egg characteristics, chick measurements, and early growth traits in ten broiler breeder strains. Poult. Sci. 86:1784–1792.[Abstract/Free Full Text]
  24. Robinson, F. E., M. J. Zuidhof, and R. A. Renema. 2007. Reproductive efficiency and metabolism of female broiler breeders as affected by genotype, feed allocation and age at photostimulation: 1. Pullet growth and development. Poult. Sci. 86:2256–2266.[Abstract/Free Full Text]
  25. Robinson, F. E., R. A. Renema, L. Bouvier, J. J. R. Feddes, M. Newcombe, and R. I. McKay. 1998. Effects of photostimulatory lighting and feed allocation in female broiler breeders. 1. Reproductive development. Can. J. Anim. Sci. 78:603–613.
  26. Yaissle, J., and M. S. Lilburn. 1998. Effects of dietary protein and strain on the growth of broiler breeder pullets from zero to five weeks of age. Poult. Sci. 77:1613–1619.[Abstract/Free Full Text]
  27. Hudson, B. I., R. J. Lien, and J. B. Hess. 2000. Effects of early protein intake on development and subsequent egg production of broiler breeder hens. J. Appl. Poult. Res. 9:324–333.[Abstract/Free Full Text]
  28. Wilson, J. L., F. E. Robinson, N. A. Robinson, and R. T. Hardin. 1995. Effect of feed allocation on female broiler breeders. J. Appl. Poult. Res. 4:193–202.[Abstract/Free Full Text]




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