J APPL POULT RES 2007. 16:27-38
© 2007 Poultry Science Association
Relationships of Body Weight, Feathering, and Footpad Condition with Reproductive and Carcass Morphology of End-of-Season Commercial Broiler Breeder Hens
R. A. Renema1,
F. E. Robinson,
R. M. Beliveau,
H. C. Davis and
E. A. Lindquist
Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5
1 Corresponding author: robert.renema{at}ualberta.ca
 |
SUMMARY
|
|---|
Reproductive efficiency of broiler breeder hens declines with age. Whereas careful feed management can maximize BW uniformity at housing, there is variability in how rate of lay and flock behavioral dynamics will interact with subsequent growth during the breeder phase. This study characterized differences in carcass and reproductive morphology in end-of-cycle commercial broiler breeder hens based on BW, feather coverage, and footpad condition, and we discuss the potential implications of the findings. At 62 wk of age, 537 hens were studied from an original flock of 3,800. Birds were sorted into subgroups based on BW, feather score, footpad score, and whether they were in laying condition when dissected. The average flock BW was 3.56 kg, with means of 2.86, 3.56, and 4.20 kg for the low (LOW), standard (STD), and high (HIGH) BW groups, respectively. A higher proportion of birds from the STD (85%) and HIGH (81%) groups still had a fully formed reproductive tract compared with birds of the LOW (59%) group. The LOW birds in laying condition had a smaller ovary than the STD or HIGH birds. The ovary condition of birds in laying condition was not related to feather coverage. As feather coverage improved, final hen BW increased, demonstrating a potential role of feather coverage in growth efficiency or of BW in level of mating activity. Birds that received a feather score of 5 (complete back feather coverage) and had a normal reproductive tract made up 14.7% of this flock. It is likely that many of these birds were mating very infrequently or possibly not mating, which has implications for maintenance of flock fertility. Some may also have been returning from a molt. Footpad condition was not related to body size. External traits such as BW, feather score, and footpad score can provide insight into flock reproductive condition and male:female interaction.
Key Words: broiler breeder hen • body weight • ovarian morphology • feather coverage • welfare
|
DESCRIPTION OF THE PROBLEM
|
|---|
Broiler breeder females face the challenge of efficiently producing settable hatching eggs despite having originated from genetic stocks intensely selected for efficient meat production. Because of selection for broiler growth rate, feed conversion, and breast muscle, reproductive performance can be compromised unless quantitative feed restriction programs are used during both the rearing and laying periods.
With continual improvements in broiler growth potential, the degree of feed restriction needed to keep breeder hens on the recommended BW targets is increasing. The increased feeding competition that can result may negatively affect flock BW uniformity during both rearing and lay. Maximizing BW uniformity by the end of the growth period can enable a high proportion of birds to respond in a similar fashion to feed and management decisions. Photostimulating a flock with poor uniformity can hinder the reproductive development of the smaller birds, which are still growing [1]. Following the onset of lay, initial BW differences can be compounded by rate-of-lay effects.
It is assumed that breeder females that have BW gains in accordance with breeder targets attain higher rates of egg production due to more orderly recruitment of follicles and a more normal synchrony between the processes of ovulation and oviposition. Overfeeding can lead to the development of multiple hierarchies, which can disrupt normal ovarian function [2, 3]. Problems such as erratic laying, poor shell quality, a high incidence of double-yolk eggs and reduced settable egg production, ovarian regression, follicular atresia, internal ovulation, and internal oviposition are other complications arising from poor control over reproduction that results from excessive ovarian development [4, 5].
The role of BW variation on carcass and ovarian morphology has been described during the sexual maturation period [1, 6], but limited description of the effect on traits at the end of lay is available [7], particularly in commercial flocks. Bjerstedt et al. [8] reported that 19.3% of end-of-lay Leghorns studied had 1 or more of the previously mentioned disorders, with ovarian regression and internal ovulation accounting for 70% of observed problems. Because the economic benefits of retaining breeder hens past 62 wk of age is reduced due to decreasing egg production and hatchability, it is important to define the factors that are contributing to this decrease in reproductive efficiency. Infertility may result from poor mating efficiency, and poor footpad condition may cause discomfort that could potentially disrupt feeding or mating behavior. To assess these questions, this study characterized differences in carcass and reproductive morphology in end-of-cycle commercial broiler breeder hens based on BW, feather condition, and footpad condition. A second objective of this study was to determine the relationship among BW, feather condition, and footpad condition with the incidence of reproductive disorders.
|
MATERIALS AND METHODS
|
|---|
Stocks and Management
The hens studied in this project were sampled from a commercial flock of 3,800 Hubbard Hi-Y [9] broiler breeders situated in central Alberta, Canada. The birds were housed under light-tight conditions during rearing and lay. Pullets were reared initially with a photoperiod of 24L:0D until 3 d of age, followed by 8L:16D through to 23 wk. Birds were photostimulated (10L:14D) at 23 wk during the month of May. The light period was subsequently increased by 1 h/wk to a maximum of 14L:10D at 26 wk of age. Standard, wheat-based commercial breeder rations were used throughout the life of the flock. Birds were full-fed until 21 d when skip-a-day feeding began and continued to until 19 wk. After 19 wk, birds were fed daily, with feed allocation changing to meet breeder recommended BW targets. At 5% production, feed was increased to 127 g/bird, with a subsequent increase of 2.2 g/bird for every 5% increase in production to a maximum of 159 g/bird at approximately 65% production. Postpeak reduction in feed allocation was based on BW and production, following breeder target BW guidelines. Chlorinated water was provided with nipple drinkers during the daylight period throughout rearing and breeding. Birds were housed in a traditional two-thirds slated-floor housing system with straw litter and a stocking density of 0.167 m2/bird. Female feeder space per bird was above standard recommendations. At the time of this study, the male flock was made up of 7.5 original and 2.0 replacement (spiking) males per 100 females.
On the evening before the flock was dispersed at 62 wk of age, a 1.2-m high solid partition was positioned 10 m from one end of the barn to isolate a random group of hens for the study. These 537 hens were not fed the following morning to ensure that dissected carcass weights would not be confounded by the presence of feed in the gastrointestinal tract. The experimental protocol was approved by the University of Alberta Faculty of Agriculture, Forestry, and Home Economics, Animal Policy and Welfare Committee under the guidelines of the Canadian Council on Animal Care [10].
Parameters Measured
All birds were individually weighed and identified with a leg band. External measurements of each hen included thoracic circumference (girth), shank length, keel length, feather coverage, and footpad condition. External measures were taken in accordance with the methods of Griffin et al. [11]. Girth was measured with a flexible, plastic measuring tape around the approximate widest point of the chest. The measurement was taken during exhalation, to the nearest 0.5 mm. Shank length was measured from the top of the flexed hock joint to the bottom of the footpad. Keel length was measured from the hypocleidoclavical joint to the caudal end of the sternum with calipers. The BW:shank was calculated as an index of bird density [11]. The intent for this measure was to have a representation of fleshing and fatness that could reduce variability due to frame size and be measured in a field setting.
Feather coverage of the back of each hen was scored on a scale of 1 to 5, following modification to the system reported by Sikur et al. [12]. A feather score of 1 indicated hens with completely bare backs and no feather coverage; a score of 2 indicated hens with bare backs and some feather coverage over the tail area; a score of 3 described hens with obvious bare patches across the midsection; a score of 4 described hens with a small bare patch in center of back; and a score of 5 designated hens with completely feather-covered backs, no worn or bare patches, and no areas of broken or new feathers.
Birds were scored on a scale of 1 to 3 based on condition of footpad [13]. A footpad score of 1 was for feet in poor condition with blood, open sores, or severe lesions; a score of 2 was for average footpad condition with few open sores or swollen lesions; and a score of 3 indicated that the feet were in normal condition with little to no abnormalities.
The weight of the abdominal fat pad (including the fat surrounding the gizzard) and the oviduct were recorded. Visual examinations for evidence of internal ovulation, internal oviposition, or both were recorded. The ovary was removed, weighed, and dissected. The number of large yellow follicles (LYF; >10 mm in diameter) and the weight of the ovarian stroma were recorded. The incidence of follicular atresia (a state of dissolution of 1 or more large follicles) and ovarian regression (no LYF) was assessed [1].
Statistical Analysis
Hens were sorted into 3 BW groups representative of the range in BW present [low (LOW; <3,100 kg); standard (STD; 3.101 to 4,000 g), and high (HIGH; >4,000 g)]. In addition, birds were sorted into 5 feather score groups (score of 1 to 5) and 3 footpad score groups (score of 1 to 3).
The data from all hens were used for analysis of carcass morphology traits. A subset of hens that were in laying condition at the time of the study (had an ovary weight of at least 15 g and had at least 1 LYF) was assessed for both carcass and reproductive morphology traits. The data were analyzed using SAS [14] with standard statistical methods [15]. Significance was assessed at the P 
0.05 level.
|
RESULTS AND DISCUSSION
|
|---|
Birds Sorted by BW
The analysis of the data set sorted by 62-wk BW is presented in Table 1
. The BW profile of the 537 hens assessed in this study had a normal distribution with a mean BW of 3.56 kg (Figure 1). The mean BW for the LOW, STD, and HIGH groups were 2.76, 3.54, and 4.20 kg, respectively (Table 1). Flock BW uniformity was calculated as 60.9% at the ±10% level and 89.4% at the ±20% level. Ultimately, the STD group was comprised of 71.1% of the hens in the study (±12.7% of mean BW).
View this table:
[in this window]
[in a new window]
|
Table 1. Mean values (±SEM) for carcass and reproductive traits of 62-wk-old broiler breeder hens (all birds or birds in laying condition) sorted into 3 BW classes
|
|
View larger version (25K):
[in this window]
[in a new window]
|
Figure 1. Frequency distribution of the total population of 537 broiler breeder hens (62 wk of age) sorted into 3 BW groups (LOW, STD, and HIGH) indicating laying condition.
|
|
A key objective of this study was to determine which hens were still in active lay at the end of the production cycle. A higher proportion of birds from the STD (85%) and HIGH (81%) groups still appeared to be in laying condition at 62 wk than in the LOW (59%) group (Table 1
). Within the LOW BW group, most of the birds out of production were below the mean BW of this group (Figure 1). A greater incidence of ovarian regression in smaller birds was also found in a subsequent study [16]. In a similar study carried out with 62-wk-old Leghorn hens, it was found that the incidence of ovarian regression was highest in hens that had a BW lower than the flock mean BW [8]. The distribution of nonlaying birds throughout the population was even wider than expected (Figure 1). It was anticipated that the target BW STD hens would have much less than the observed level of 15% of birds out of lay. In contrast, the HIGH group had more birds in active lay than expected. The potential for obesity-related reproductive disorders, leg problems, and other traits typically associated with overfed birds [17] was expected to hurt the reproductive status of these birds. However, although larger, these birds appeared very capable of maintaining active lay. The 62-wk BW mean of the birds dissected was 3.56 kg. This may have both reduced the incidence of obesity-related disorders and increased the incidence of birds no longer in egg production at the end of the breeder period. Interpretations from this study must be applied accordingly when compared with other breeder operations.
The BW differences among the BW class groups also resulted in differences in all external skeletal size parameters (girth, keel length, and shank length; Table 1). Even when the BW:shank was used to eliminate some of the variability due to frame size, values increased from the LOW to the STD and HIGH groups in the comparison of all birds (26.2, 32.5, and 37.6 g/mm, respectively), with similar values for birds in laying condition. These differences indicate that the degree of fleshing increased with body size. A concern with the larger hens is that excess fleshing will result in an increased metabolic maintenance requirement to maintain the extra muscle. However, it may also be the natural result of a hen either growing more efficiently or having a more aggressive eating behavior compared with the smaller birds.
The single, largest factor influencing final BW is rate of lay. In addition, there can be a high degree of variation in maintenance requirements, with less efficient hens demonstrating a higher regulatory thermogenesis, resulting in dissipation of excess energy as heat [18]. Variation in maintenance requirement may be attributed to differences in body composition. This can be affected by bird genetics, behavior, and management and may affect fat and protein deposition in body tissues, lipid metabolism, egg composition, and the size and metabolic rate of the liver, gut, and reproductive tract. The liver, gut, and reproductive tract alone represent 26 and 30% of the total energy expenditure in fed and fasted broiler breeder hens, respectively [19]. Following the substantial impact of rate of lay, differences in both size and metabolic rate of these organs can have a substantial effect on overall maintenance requirements.
In the comparison of all birds, the abdominal fatpad of the heavier birds represented a greater proportion of BW than it did in the smaller birds (LOW, 1.84%; STD, 3.25%; HIGH, 4.15%; Table 1). The equivalent data for hens in production were very similar, suggesting that the nonlaying hens had a comparable level of fatness. Once hens ceased laying, the concern was that they would simply get fat and skew the carcass trait comparisons—particularly fatness. This did not appear to be the case in this flock.
The weights of the abdominal fatpads for birds of all BW classes were relatively low compared with previously reported values. Renema et al. [7] reported that 61-wk-old caged breeder hens managed on 3 BW profiles (control and ±150 g of target BW) had mean abdominal fat pad values of 4.46% (low curve) to 5.69% (high curve). In a comparison of genetic strains at 53 wk of age, mean fat pad mass has been reported to be 4.8 to 4.9% of BW [20]. Despite similar BW profiles, caged hens could conceivably be fatter than floor-housed hens due to differences in activity level. The producer managing the breeder flock of the current study uses a slightly lighter BW target than usual for Hubbard Hi-Y hens during the final phase of the breeder period, which likely contributed to the leanness of these hens.
The oviduct weight was very consistent among birds of all BW classes, averaging 59.2 g (Table 1). This fits previous observations about similarities in oviduct weight across body size groups [1]. However, ovary and ovarian stroma weights were lower in LOW hens compared with the 2 heavier groups of hens (Table 1). These differences were also reflected in LYF numbers, in which the LOW hens had fewer LYF (5.2) than the STD (5.6) hens. Renema et al. [1] suggested that a naturally high incidence of small-follicle atresia in low-weight birds at sexual maturity may limit the ability of the ovary to generate an adequate number of LYF to maintain comparable rates of egg production to the heavier bird groups. Within restricted-fed birds in their study, they reported a numerical reduction of 1.2 LYF at the onset of lay in birds 20% light at photostimulation compared with control or 20% heavy birds [1]. Low-weight birds can have reduced egg production due to a delayed onset of lay [4].
The incidence of LYF atresia ranged from 0.03 follicles in LOW hens to 0.24 follicles in HIGH hens (Table 1). Variability among birds for this parameter limited the significance of this comparison (P = 0.081). Lower rates of follicular atresia in smaller birds have previously been reported [7]. If a reduced rate of growth efficiency or higher maintenance requirement is limiting the ability of the LOW birds to grow, allocation of nutrients to support ovarian follicle production could be similarly affected. This would explain the reduced ovary size, LYF production, and rates of follicular atresia in LOW birds. The incidence of internal ovulation and internal lay was similar for all 3 BW groups, and the values were very low.
Birds Sorted by Feather Score
The numbers of birds in each of the 5 feather score group varied from 25 (score of 1) to 152 (score of 3), as seen in Table 2. Birds in the FS5 group (complete back feather cover with no broken feathers in saddle area) had the most birds out of laying condition. The distribution of feather scores among the HIGH birds was shifted toward higher values (better feather coverage) than the STD birds when compared across all birds (Table 3). However, when just birds in reproductive condition were compared, the distribution of scores from the HIGH birds differed from that of both the LOW and STD groups. Within the LOW group, only 27% of birds with perfect feathering (FS5) were in laying condition compared with a mean value of 74.8% for the 2 heavier BW classes (Table 3).
View this table:
[in this window]
[in a new window]
|
Table 2. Mean values (±SEM) for carcass and reproductive traits of 62-wk-old broiler breeder hens (all birds or birds in laying condition) sorted by feather score
|
|
View this table:
[in this window]
[in a new window]
|
Table 3. Incidence of specific feather scores of 62-wk-old broiler breeder hens (all birds or birds in laying condition) sorted into 3 BW classes1
|
|
There were no differences in BW among the 5 feather score groups when the entire flock data set was assessed (Table 2). However, when just the birds in laying condition were examined, the birds with the best feather condition (FS5) were heavier than birds with less feather coverage (FS1, FS2, and FS3). In the laying birds, several measures of frame size (chest girth, shank length, and BW:shank length) illustrated that the most poorly feathered birds were also the smallest (Table 2). Whereas values for relative abdominal fat pad differed significantly, the magnitude of these differences was small and did not show a clear pattern.
The lack of feather coverage may have contributed to BW differences. Neme et al. [21] reported a higher maintenance requirement and a general increase in the lower critical temperature in laying pullets with poor feather coverage compared with fully feathered birds in temperatures below 18°C. Despite 62 wk of age occurring in February, low temperature was not a factor in the current study, because birds were housed in a heated, insulated barn with good environmental controls. Despite having a smaller BW, hens in the FS2 group had a heavier oviduct and a higher proportion of abdominal fat than the FS5 birds (Table 2). Eating behavior, nutrient utilization efficiency, rate of lay, or even estrogen status may be additional factors modulating carcass and reproductive traits by the end of the breeder period. Further investigation into the growth and reproductive history of individual birds may provide more insight into the potentially greater contribution of FS2 birds to the reproductive success of the flock.
Male size and aggressiveness may have contributed to reduced feather coverage of smaller birds. Larger males are more likely to initiate forced matings [22]. Alleviating hunger through ad libitum feeding males nearly doubles the aggressive acts toward females [23]. Large females may have better feather condition because they are more difficult for the males to aggressively target. It has also been suggested that dominant mature hens may be less likely to be mated because they intimidate the males—perhaps causing some degree of psychological castration to the males [24] traditionally. Psychological castration has been described in terms of male-to-male interactions [22].
In a commercial male flock characterized at 63 wk of age, original and replacement (spiking) males weighed 4,573 g compared with 4,096 g, respectively [13]. This is 23 and 10% heavier than the 62-wk-old laying females of the FS5 category in the current study. Allowing an extra 5 wk of growth would allow the FS5 hens to grow even closer in BW to those reported for males. Maximizing female BW uniformity by the end of the rearing period can positively affect rate of lay [25]. The current study suggests that tightening BW uniformity may also influence flock mating behavior.
Within the HIGH BW class, 31% of the birds in reproductive condition were in the FS5 group (Table 3). Feather quality and the degree of feather coverage were theorized to be indicative of mating activity, because they result in feather damage and loss from the back of the hen. Although the proportion of birds in the FS5 group was lower in the STD (16%) and LOW (10%) groups, on a flock basis, these perfectly feathered birds with functional ovaries represented 14.7% of the flock. This suggests that many of these birds were either being mated very infrequently or not at all. The potential for having large numbers of unmated or rarely mated females near the end of lay on fertile egg production warrants further investigation to determine which possibility is true. Hens actively avoiding the males may contribute to this finding. It is also likely that some of these superior feathered hens may have undergone a molt and come back into production. A subsequent investigation included assessment of vent area feathering in hens with excellent back feathering [16]. Feathering in the vent area demonstrated evidence of mating activity in birds with a functional reproductive tract, whereas those with a regressed ovary did not. With further validation, back feather score may be a useful indicator of mating frequency.
The effect of hen BW on male mating preference and behavior is not well understood. The dominant hens have long been known to have both greater freedom of the pen and freer access to feed [26]. The dominant males do not mate with all of the same hens the subordinate ones do and will actively suppress the sexual activity of their inferiors [27], which will ultimately influence the mating frequency of specific hens. Guhl and Warren [27] found that 35% of hens that males mated infrequently had fertility of 50% or less. Because males will preferentially mate with females with large sexual ornamentation (comb size) [28], this may be a reproductive hormone-based effect and linked to female quality. A lack of estrogen in hens with a regressing ovary leads to a decrease in breeding activity [29] and eventually to a molt.
Despite differences in feather score, all birds that were laying had similar reproductive tract morphology (Table 2). This suggests that feather score was not a good indicator of laying status. This may indicate that mating activity as it relates to feather condition is not closely linked to internal reproductive condition based on the traits examined in this study. There were no significant differences in ovary weight, number of LYF, or atretic LYF among the feather score groups (Table 2). The FS5 hens were the only group to show a trend toward differing reproductive morphology due to an ovarian stroma and oviduct weight that were below that of several other groups. Because ovary weight and LYF number were not affected, the smaller stroma size may be an early indicator of impending reduced reproductive potential. In a comparison of full-fed to restricted-fed hens, differences in bare stroma weight (follicles >1 mm in diameter removed) may indicate differences in the population of prehierarchical, estradiol-17ß-producing follicles [1]. This would affect the total estradiol-17ß output of the ovary. A difference in ovarian reproductive hormone output could provide a basis for an endocrine link to mating behavior.
Birds Sorted by Footpad Score
A similar number of hens received each footpad score (Table 4). Interestingly, the heaviest BW class birds did not have poorer foot condition, indicating that higher weights were not contributing to worse footpad condition in this flock. The footpad scores were evenly distributed among the 3 BW classes (Table 5). In an assessment of male foot condition at 62 wk of age, Wolanski et al. [13] suggested that both age and high BW appeared to have a negative effect on footpad condition. Good footpad condition may be more essential in the male than in the female due to the frequency of mating and the physical role of the male in the mating process. Improper temperature, ventilation, and litter conditions are known to adversely affect footpad condition [30].
View this table:
[in this window]
[in a new window]
|
Table 4. Mean values (±SEM) for carcass and reproductive traits of 62-wk-old broiler breeder hens (all birds or birds in laying condition) sorted by foot score
|
|
View this table:
[in this window]
[in a new window]
|
Table 5. Incidence of specific foot scores of 62-wk-old broiler breeder hens (all birds or birds in laying condition) sorted into 3 BW classes1
|
|
Footpad condition appears to be a factor in determining if birds will remain in active lay to the end of the breeder period. Only 72% of the hens in the FPS1 group (poorest footpad condition) were in lay, compared with 88 and 85% for the FPS2 and FPS3 groups, respectively. Birds with the best footpad condition (FPS3) had a marginally smaller frame size (keel length and shank length) than the other 2 groups. A causative relationship between frame size and footpad score cannot be made based on the data assessed, but this area may be worthy of further study. There was evidence to suggest that hens with the poorest footpad condition were leaner, because abdominal fat pad weight was reduced in these birds (Table 4). This may be a consequence of reduced mobility at feeding time due to discomfort relating to their footpad condition.
For birds in laying condition, there was no difference in oviduct weight, ovary weight, stroma weight, or the number of LYF among footpad score groups (Table 4). Although there was no difference in the incidence of internal lay or LYF atresia, the FPS1 hens had a higher incidence of internal ovulation (9.4% of birds) than the FPS3 hens did (3.4% of birds). This difference is less dramatic when the internal ovulation and the related internal lay values are combined as a measure of evidence for ovulation not resulting in an egg (10.1 vs. 6.8% of FPS1 and FPS3 hens, respectively). Evidence for internal ovulation and particularly for internal lay may remain in the bird for some time after the event. A less-developed oviduct may contribute to increased rates of internal ovulation, although the oviduct weight of the FPS1 birds was only numerically reduced (Table 4).
|
CONCLUSIONS AND APPLICATIONS
|
|---|
- The LOW hens were the least likely to be in laying condition (regressed ovary in 41% vs. mean of 17% for STD, and HIGH hens).
- Within this flock, over 21% of the hens were assessed a perfect feather score of 5, indicating that they were mating, mating infrequently, returning from a molt, or not molting. Ovarian regression was apparent in 31% of these birds, whereas the remaining well-feathered birds (representing 14.7% of this flock) were reproductively fit.
- In the HIGH BW class, a disproportionately high number of birds had perfect feathering, suggesting that the larger hens were not being mated as much as lower BW hens. It is not clear how much the role of male size and female selection plays in this result compared with the role of female behavior (avoidance of or aggression toward males).
- In the group with the worst footpad condition, 28% of the flock was out of lay, compared with 12 and 15% for the intermediate and best footpad groups, respectively.
- External traits such as BW, feather score, and footpad score can provide insight into how birds have changed during the breeding period, flock reproductive condition, and male:female interaction.
|
ACKNOWLEDGMENTS
|
|---|
The donation of hens, cooperation, and help of T. Fast of Terad Farms, Ferintosh Alberta, Canada, for this on-farm study are gratefully acknowledged. Thanks to K. van Middelkoop for helpful discussions on issues of flock behavioral dynamics. Special thanks to the staff and students of the Alberta Poultry Research Centre for their assistance.
|
REFERENCES AND NOTES
|
|---|
- 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. 2. Ovarian morphology and plasma hormone profiles. Poult. Sci. 78:629–639.[Abstract/Free Full Text]
- van Middelkoop, J. H. 1972. The relationship between ovulation interval of White Plymouth Rock pullets and the laying of abnormal eggs. Arch. Geflugelkd. 36:223–230.
- Hocking, P. M., D. Waddington, M. A. Walker, and A. B. Gilbert. 1989. Control of the development of the ovarian follicular hierarchy in broiler breeder pullets by food restriction during rearing. Br. Poult. Sci. 30:167–174.
- Robinson, F. E., N. A. Robinson, and T. A. Scott. 1991. Reproductive performance, growth and body composition of full-fed versus feed restricted broiler breeder hens. Can. J. Anim. Sci. 71:549–556.
- 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 production. Poult. Sci. 71:1750–1761.[Web of Science][Medline]
- Renema, R. A., F. E. Robinson, M. Newcombe, and R. I. McKay. 1999. Effects 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]
- Renema, R. A., F. E. Robinson, P. R. Goerzen, and M. J. Zuidhof. 2001. Effects of altering growth curve and age at photo-stimulation in female broiler breeders. 2. Egg production parameters. Can. J. Anim. Sci. 81:477–486.
- Bjerstedt, H. L., F. E. Robinson, R. T. Hardin, and T. A. Wautier. 1995. Carcass traits and reproductive organ morphology in 62-week-old SCWL hens. Can. J. Anim. Sci. 75:341–344.
- Hubbard-ISA. Duluth, GA.
- Canadian Council on Animal Care. 1984. Guide to the Care and Use of Experimental Animals. Vol. 2. CCAC, Ottawa, Ontario, Canada.
- 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]
- Sikur, V. R., F. E. Robinson, D. R. Korver, R. A. Renema, and M. J. Zuidhof. 2004. Effects of nutrient density on growth and carcass traits in fast- and slow-feathering female turkeys. Poult. Sci. 83:1507–1517.[Abstract/Free Full Text]
- Wolanski, N. J., R. A. Renema, F. E. Robinson, and J. L. Wilson. 2004. End-of-season carcass and reproductive traits of original and replacement male broiler breeders. J. Appl. Poult. Res. 13:451–460.[Abstract/Free Full Text]
- SAS Institute. 2002. SAS/STAT User’s Guide. Version 9.1. SAS Inst. Inc., Cary, NC.
- Body weight and carcass characteristic data were analyzed by 1-way ANOVA [14] comparing the quantitative data from the 3 body size class groups, the 5 feather score groups, and the 3 footpad groups. All qualitative, subjective, or both qualitative and subjective scoring data (incidence of reproductive problems, feather score, footpad score) underwent 2 analysis using Fisher’s exact test [14]. Significance was assessed at the P < 0.05 level.
- Robinson, F. E. 2006. University of Alberta, Edmonton, Alberta, Canada. Personal communication.
- Renema, R. A., and F. E. Robinson. 2004. Defining normal: Comparison of feed restriction and full feeding of female broiler breeders. World’s Poult. Sci. J. 60:511–525.
- 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.[Web of Science][Medline]
- 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]
- Joseph, N. S., F. E. Robinson, R. A. Renema, and M. J. Zuidhof. 2002. The effects of age at photostimulation on reproductive efficiency in three strains of broiler breeders varying in breast yield. J. Appl. Poult. Res. 11:308–319.[Abstract/Free Full Text]
- Neme, R., N. K. Sakomura, F. B. Fialho, E. R. Freitas, and E. H. Fukayama. 2005. Modeling energy utilization for laying type pullets. Braz. J. Poult. Sci. 7:39–46.
- Bilcik, B., and I. Estevez. 2005. Impact of male-male competition and morphological traits on mating strategies and reproductive success in broiler breeders. Appl. Anim. Behav. Sci. 92:307–323.[Web of Science]
- Millman, S. T., I. J. Duncan, and T. M. Widowski. 2000. Male broiler breeder fowl display high levels of aggression toward females. Poult. Sci. 79:1233–1241.[Abstract/Free Full Text]
- van Middelkoop, J. H. 2005. Koside, ’s-Hertogenbosch, The Netherlands. Personal communication.
- Hudson, B. P., R. J. Lien, and J. B. Hess. 2001. Effects of body weight uniformity and pre-peak feeding programs on broiler breeder hen performance. J. Appl. Poult. Res. 10:24–32.[Medline]
- Masure, R. H., and W. C. Allee. 1934. The social order in flocks of the common chicken and the pigeon. Auk 51:306–327.
- Guhl, A. M., and D. C. Warren. 1946. Number of offspring sired by cockerels related to social dominance in chickens. Poult. Sci. 25:460–472.[Web of Science]
- Pizzari, T., C. K. Cornwallis, H. Løvlie, S. Jakobsson, and T. R. Birkhead. 2003. Sophisticated sperm allocation in male fowl. Nature 426:70–74.[Medline]
- Barfield, R. J. 1979. The hypothalamus and social behavior with special reference to the hormonal control of sexual behavior. Poult. Sci. 58:1625–1632.[Web of Science][Medline]
- Ekstrand, C., T. E. Carpenter, I. Anderson, and B. Algers. 1998. Prevalence and control of foot pad dermatitis in broiler in Sweden. Br. Poult. Sci. 39:318–324.[Web of Science][Medline]
TOP
SUMMARY
DESCRIPTION OF THE PROBLEM
