Effect of Flock Age and Postemergent Holding in the Hatcher on Broiler Live Performance and Further- Processing Yield

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1 2005 oultry Science Association, Inc. Effect of Flock Age and ostemergent Holding in the Hatcher on Broiler Live erformance and Further- rocessing Yield N. S. Joseph and E. T. Moran, Jr. 1 Department of oultry Science, Auburn University, Auburn, Alabama rimary Audience: Hatchery Managers, Live roduction Supervisors, rocessing lant Managers, Researchers SUMMARY Chicks held in an incubator or hatcher for an extended period of time prior to removal will reduce body weight, yolk sac reserves, and immune function while increasing the risk of dehydration and death. This experiment was conducted to compare the quality and subsequent performance of early-emerging chicks that were held in the hatcher vs. those that emerged just prior to removal. Eggs were obtained from young (32 wk) and prime age (41 wk) Ross Ross 308 breeder flocks. The mean incubation length of early-hatched chicks was 497 h compared with 509 h for latehatched chicks, resulting in an average postemergent duration of 15 h vs. 3 h in the hatcher, respectively. Total chick yield was similar between young and prime flocks (82 and 83% of eggs set, respectively), but proportionately, the prime flock produced more early-hatch chicks than the young flock. Higher whole body weight and yolk sac weight at hatch were associated with late emergence. Chick body weights after access to feed and water for 1 wk continued to be at a disadvantage for birds from young hens, whereas early-hatched chicks were similar to late-hatched chicks. Males and females responded similarly to flock age and hatch treatments. By 6 wk of age, higher total feed conversion and carcass abdominal fat existed with broilers from prime compared with those from young breeders, whereas yields of skinless boneless breast meat were similar. rolonged holding in the hatcher had no major effects on final live performance, carcass quality, or breast meat yield. Key words: broiler, flock age, hatch time, live performance, carcass yield 2005 J. Appl. oult. Res. 14: DESCRITION OF ROBLEM It is common practice to keep early-emerging chicks in the incubator or hatcher until nearly all the chicks have hatched, as it is more efficient to remove and process them all at once. However, chicks being held in the hatcher for an extended period of time can lead to dehydration, diminished yolk sac reserves, and increased ex- cretion [1, 2] all of which can reduce body weight [1, 3, 4, 5]. Chicks held in the hatcher also have lower bursa and spleen weights [4, 5], higher total plasma protein levels and heterophil:lymphocyte ratios [5], and higher mortality before [6] and after placement [6, 7, 8]. Chicks from older flocks are more likely to be affected because incubation length decreases as hen age increases [9, 10, 11, 12, 13]. Wyatt 1 To whom correspondence should be addressed: moranet@auburn.edu.

2 JOSEH AND MORAN: FLOCK AGE AND HATCH TIME 513 et al. [4] found that broiler chicks from an older breeder flock began hatching 6 h sooner than chicks from a younger flock. Because a greater proportion of chicks originating from older breeders will hatch earlier, they may be of poor quality if held in the hatcher for the same length of time as chicks from a younger breeder flock. rolonged holding in the hatcher can lower chick quality; therefore, the practice of keeping early-hatched chicks in the hatcher until latehatched chicks have emerged has been discouraged [1, 3, 4]. However, in the broiler industry, the feasibility of changing a hatchery practice is likely to depend on whether the quality of the final product in the processing plant is affected by prolonged holding in the hatcher. Therefore, the objective of this experiment was to evaluate the effect of flock age and prolonged holding in the hatcher on chick quality, live performance, and carcass characteristics of broiler chickens at 6 wk of age. MATERIALS AND METHODS The Auburn University Institutional Animal Care and Use Committee approved the experimental protocol. Ross Ross 308 eggs were obtained from a single breeder complex. The breeder flocks were 32 wk of age (young) and 41 wk of age (prime). Sixty eggs per flock age were randomly chosen for measurement of egg characteristics. Nine hundred eggs from each flock were weighed by groups of 15 (equivalent to 60 replicates) and set in a single-stage incubator [14]. At 18 d of incubation, those eggs deemed infertile by candling were removed. The remainder from each group was transferred to hatch baskets (plastic perforated trays) and placed in a hatcher [14]. The eggs were incubated at 37.0 C (and 54% RH) instead of 37.5 C to extend the duration of the incubation period [15] with the intention of widening the gap between early- and late-emerging chicks. To differentiate early-emerging chicks from late-emerging chicks, approximately every 4 h beginning at 480 h of incubation (i.e., 20 d), dry and saleable (healthy) chicks were feathersexed, marked, weighed, and placed back inside the hatcher. Chicks hatching between 480 and 504 h were grouped into the early-hatch treatment. Beginning at 506 h of incubation, the procedure was repeated at approximately 4-h intervals with the resulting chicks grouped into the late-hatch treatment. To create separation between hatch treatments, chicks hatched from 504 to 506 h were not used for the trial. During this process, the hatcher was opened frequently, which likely affected incubation length by lowering the temperature and relative humidity inside the incubator. However with the incubator used for this study, it could not be avoided. The process was done swiftly (less than 2 min) each time to minimize disturbance to the incubator environment. At 512 h of incubation, all of the chicks were removed, weighed once more, vaccinated for Marek s disease, and kept in the hatchery for 9 h before placement. The next day, sample chicks from each treatment were euthanized with CO 2 gas and then dissected to determine yolk sac weight and yolk-free body weight. To assess initial live performance and carcass characteristics 504 chicks were placed in 72 battery cages (0.07 m 2 /chick) providing 9 replicate cages per hatch time, flock age, and sex. Water and a common corn-soybean meal starter ration (3,070 kcal/kg of ME, 22.5% C) were supplied ad libitum under continuous lighting. Dissection of a subsample of these chicks at 3 d of age (1 chick/replicate cage) allowed for determination of yolk sac weight at 8 d of age (2 chicks/ replicate cage) and bone-in breast and liver weights. Because the breast muscles (pectoralis major and minor) were minimally developed at 1 d of age, inclusion of the frame (furculum, rib cage, and keel) during dissection at 1, 3, and 8 d of age provided a more consistent measure of breast weight. To determine live performance and processing yield, 576 chicks were placed in 32 floor pens (providing 4 replicate pens per hatch time, flock age, and sex) for 6 wk. Initially, there were 18 chicks per pen, but at 8 d of age remaining chicks from the battery cages were added to the floor pens to provide 25 chicks per pen (0.16 m 2 /bird). Chicks were fed common corn-soybean meal rations throughout rearing. The starter ration (3,070 kcal of ME/kg, 22.5% C) was fed from 0 to 16 d of age, the grower ration (3,150 kcal of ME/kg, 20% C) from 17 to 32 d of age, and the finisher ration (3,200 kcal of ME/kg, 18.7% C) from 33 to 42 d of age. Feed consumption and individual body weights were

3 514 JAR: Research Report TABLE 1. Characterization of broiler eggs originating from young and prime age breeder flocks 1 Egg Item weight (g) Shell Yolk Albumen (% egg weight) Without covariate Young rime SEM *** NS *** *** With covariate Young rime SEM NS *** *** Egg weight NS * * 1 : Young = 32 wk of age, rime = 41 wk of age. Values represent the least squares means of 60 eggs randomly sampled from each source, analyzed with and without egg weight as a covariate. * 0.05; *** 0.001; NS = > determined when the rations were changed. Mortality was recorded daily. At 6 wk of age, birds were cooped, held for 12 h, and then processed in the poultry processing plant at the university. After immersion in chilled ice water for 3 h, carcasses were drained, and abdominal fat pads were removed. Breast fillet and tenders were removed 24 h postmortem by experienced personnel using stationary cones. Our statistical analysis is described in the References and Notes section [16]. RESULTS AND DISCUSSION Egg Characterization and Hatchability The prime flock had a heavier mean egg weight than the young flock (Table 1). With or without taking egg weight into account, eggs from the prime flock had proportionately more yolk at the expense of albumen than eggs from the young flock, which was consistent with other reports [12, 18, 19]. Shell weight was equivalent for both flock ages. After incubation, it was found that both flocks had similar levels of fertility, and overall hatchability was not affected by flock age (Table 2). The mean incubation length for the earlyhatch treatment was 497 h vs. 509 h for the latehatch treatment, a difference of 12 h. The early-hatched chicks were in the hatcher for up to 32 h postemergence, with a mean holding time of 15 h. The late-hatch treatment was held for up to 6 h postemergence in the hatcher, with a mean holding time of only 3 h. The number of early-hatched vs. late-hatched chicks was also affected by flock age (Table 2). Eggs from the prime flock produced a greater number of earlyhatched chicks compared with the young flock, whereas the opposite occurred during the latehatch period. These results agreed with previous observations that hatch time decreased as flock age increased [9, 10, 11, 13]. The relationship between flock age and incubation length is poorly understood. It is not a function of egg weight because when egg weight is held constant, incubation length will still decrease with increasing flock age [1, 8, 20, 21]. Incubation length may relate to shell conductance and the rate of embryonic development. Older hens produce thin-shelled eggs [22, 23, 24]. Thin eggshells increase the rate of water loss [25] and eggshell conductance (the ability to respire) [26] compared with thick eggshells. Studies have also shown that embryos from older flocks are further developed at 2 d of incubation [27], have a faster rate of yolk lipid uptake [28, 29], and have greater intestinal development [30] than those from younger flocks. Christensen et al. [26] suggested that greater conductance and advanced development could place added pressure on the embryo at the plateau stage of incubation, increasing the already high demand

4 JOSEH AND MORAN: FLOCK AGE AND HATCH TIME 515 TABLE 2. Hatchability of broiler eggs from young and prime age breeder flocks 1 Hatchability (% eggs set) 2 Saleable chicks 3 (n) Fertility Source (% eggs set) All chicks Saleable chicks Early Late Young rime SEM NS NS NS *** *** 1 : Young = 32 wk of age, rime = 41 wk of age. Values represent the least squares means of 60 replicate trays of 15 eggs at the start of experimentation. 2 Number of eggs set: 900 per flock age. 3 Chicks emerged either before 504 h (Early) or after 506 h (Late) of incubation. Chicks that emerged between 504 and 506 h of incubation were not included in the data set. *** 0.001; NS = > for carbohydrate metabolism. The embryo then must either emerge early or perish. Indeed, more deaths late in incubation of chickens [31], higher pipping mortality of turkeys [26], and an overall decline in hatchability have been reported with increasing flock age [26, 31, 32, 33, 34]. Chick Weight and Quality Chick quality was assessed as BW upon final removal from the hatcher, 1-wk BW gain, and carcass characteristics at 1, 3, and 8 d of age. affected the BW at emergence and upon removal from the hatcher, which followed differences observed in egg weight (Table 3). A loss of approximately 1gofBWoccurred between emergence and removal, which in other studies has been attributed to dehydration [1, 2]. Chick carcass characteristics are presented in Table 4. At 1dofageyoung flock chicks had reduced yolk-free BW and fewer yolk sac reserves than prime flock chicks, which was expected given their small egg sizes and yolk weights [35]. At 3 d of age, young flock chicks still had a lower BW, but yolk sac weights were similar to those of prime flock chicks. At 1 d of age, holding time in the hatcher did not affect yolk-free body weight, but early-hatched chicks had smaller yolk sac reserves than chicks that hatched late. By 3 d of age, yolk sac weights were similar and early-hatched chicks weighed more than late-hatched chicks. Males and females had similar yolk-free body and yolk sac weights at 1 d of age (36 ± 0.4 g and 3.7 ± 0.15 g for BW and yolk sac weight, respectively) and at 3 d of age (59 ± 0.6 g and 1.3 ± 0.06 g, respectively). Some studies have found that males are heavier than females at hatch [36, 37, 38], whereas others, including this study, have found no sex differences in BW [2, 19, 39, 40, 41, 42]. TABLE 3. Weight of chicks originating from young and prime age breeder flocks at emergence and the subsequent loss with removal from hatcher 1 BW at emergence (g) BW at removal (g) Weight loss of Source Early Late Early Late early-hatched chicks 2 Young rime SEM *** *** *** *** * 1 : Young = 32 wk of age, rime = 41 wk of age. Body weight once chicks emerged from shell, upon removal from the hatcher, and their difference. Values represent the least squares means of chicks originating from 60 replicate groups of 15 eggs. 2 Weight loss was calculated for early-hatched chicks only because a measurable weight loss among late-hatched chicks was not detected. * 0.05; ***

5 516 JAR: Research Report TABLE 4. The effect of early vs. late emergence on yolk-free body and yolk sac weights of broiler chicks from young and prime age breeder flocks 1 1dofage 3dofage Source Body (g) Yolk sac (g) Body (g) Yolk sac (g) Young rime Hatch time Early Late SEM Young Early hatch 33.6 c c 1.3 Late hatch 35.1 bc c 1.5 rime Early hatch 38.2 a a 1.3 Late hatch 36.9 ab b 1.2 SEM *** *** *** NS Hatch time NS ** * NS hatch time * NS * NS a c Means within a column and main effect with no common superscript differ significantly. 1 : Young = 32 wk of age, rime = 41 wk of age. Values represent the least squares means of 7 and 9 replicates at1and3dofage, respectively. * 0.05; ** 0.01; *** 0.001; NS = > Female chicks tend to emerge sooner than male chicks [3, 19, 37], suggesting that females may weigh the same as males at emergence but then lose weight when held in the hatcher, thereby weighing less than males upon removal. Therefore, discrepancies in published reports regarding the sexual dimorphism of BW may be a reflection of the amount of time the chicks were held in the hatcher before they were weighed. and hatch time affected BW at 1 and 3 d posthatch. At 1 d, young flock chicks weighed less and prime flock chicks weighed more with early emergence, whereas both were of intermediate BW with late emergence. Three days later, chicks from the prime flock that emerged early were still heavier followed by those that emerged late. Chicks from the young flock weighed less, regardless of hatch time. Growth and carcass characteristics were studied at 8 d of age to determine if there were any differences in BW, bone-in breast weight, and liver weight (Table 5). rime flock chicks gained more weight than those from the young flock, whereas breast and liver weights were similar. In the present study, holding in the hatcher did not affect BW at 8 d of age because early-hatched chicks gained more weight from 1 to 8 d than those emerging late. This finding was consistent with the findings of Hager and Beane [1]. Early-hatched chicks had a greater breast weight and a lower liver weight than latehatched chicks, but as a proportion of BW, neither differed by hatch treatment. Sex differences in BW were observed at 8dofage. There was no difference in breast weight, but females had a slightly higher liver weight than males. Flock age and hatch time did not affect BW, breast weight, or liver weight at 8 d of age. Live erformance effects on BW observed at hatch and again at 8dofagehaddissipated by 16 d of age (data not shown). By 6 wk of age, birds from the prime flock were of similar BW to birds of the young flock but had a higher feed conversion (Table 6). Mortality during rearing was not affected by flock age. Total live performance, including final BW, feed conversion, and

6 JOSEH AND MORAN: FLOCK AGE AND HATCH TIME 517 TABLE 5. Effect of early vs. late emergence on initial live performance and body characteristics of broiler chicks from young and prime age breeder flocks 1 Body weight (g) Breast 2 Liver Source 8 d of age Gain Weight (g) (% BW) Weight (g) (% BW) Young rime Hatch time Early Late Sex Male Female SEM *** *** NS NS NS NS Hatch time NS * *** NS *** NS Sex * NS NS NS NS * 1 : Young = 32 wk of age, rime = 41 wk of age. Body weight values represent the least squares means of 9 replicate pens each having 7 chicks. Breast and liver values represent the least squares means of 2 chicks each from 9 replicate pens. No significant interactions ( > 0.05) were detected among main effects. 2 Breast was removed with the rib cage (bone-in). * 0.05; *** 0.001; NS = > mortality, was similar for hatch treatments. This finding was consistent with the findings of Hager and Beane [1], Williams et al. [3], and Wyatt et al. [4], who found that holding early-hatched chicks in the hatcher for up to 32, 36, and 48 TABLE 6. Effect of early vs. late emergence on total live performance of 6-wk old broilers from young and prime age breeder flocks 1 Body weight (g) h, respectively, had no effect on posthatch BW when compared with the BW of late-hatched chicks. In these studies, advantages in BW occurred only when early-emerging chicks were promptly removed from the hatcher and placed Source Final Gain Feed conversion 2 Mortality (%) Young 2,429 2, rime 2,462 2, Hatch time Early 2,443 2, Late 2,448 2, Sex Male 2,634 2, Female 2,257 2, SEM NS NS * NS Hatch time NS NS NS NS Sex *** *** *** NS Total 1 : Young = 32 wk of age, rime = 41 wk of age. Values are the least squares means of 4 replicate pens each with 25 chicks at the start of experimentation. No significant interactions ( > 0.05) were detected among main effects. 2 Feed conversion (kg of feed/kg of gain) values were corrected for mortality. * 0.05; *** 0.001; NS = > 0.05.

7 518 JAR: Research Report TABLE 7. Effect of early vs. late emergence on carcass and breast meat yield of 6-wk old broilers from young and prime age breeder flocks 1 Carcass without abdominal fat 2 Abdominal fat 3 Fillets 4 Tenders 4 Weight Live weight Weight Carcass Weight Carcass Weight Carcass Source (g) (%) (g) weight (%) (g) weight (%) (g) weight (%) Young 1, rime 1, Hatch time Early 1, Late 1, Sex Male 1, Female 1, SEM NS NS *** ** NS NS NS NS Hatch time NS NS NS NS NS NS NS NS Sex NS *** *** NS *** ** ** ** 1 : Young = 32 wk of age, rime = 41 wk of age. Values represent the least squares means of 4 replicate pens each with ca. 22 carcasses. No significant interactions ( > 0.05) were detected among main effects. 2 Carcass without neck and giblets after 4 h of ice-water chilling and removal of abdominal fat, expressed on an absolute basis and relative to full-fed live body weight. 3 Depot fat removed from the abdominal cavity expressed on an absolute basis and relative to the chilled carcass. 4 Fillets and tenders correspond to the pectoralis major and minor, respectively, and are expressed on an absolute basis and relative to the chilled carcass. ** 0.01; *** 0.001; NS = > in brooder pens. Although in the present study all of the early-hatched chicks were kept in the hatcher until hatch pull, and, therefore, the effects of hatch time and holding time could not be separated, this study is very applicable because this practice is common in industry. Sex differences in live performance were evident; males gained more weight than females and had lower feed conversion. Carcass Yield and Further rocessing Chickens originating from prime breeders had more abdominal fat than young breeders with similar carcass weights (Table 7). Chicks from older breeders have more body fat at hatch [43], which is likely influenced by yolk size. However, we did not expect to observe an effect at 6 wk of age. In one study, differences in broiler fat retention with breeder age were not observed after 7 d of age[44]. Breast fillet and tender yields were not affected by flock age. Carcass weight was not affected by hatch treatments. Abdominal fat pad weights and breast fillet and tender yields were the same for early and late-hatched chicks. Female carcasses weighed less than male carcasses and, consequently, had more depot fat as a percentage of carcass weight. Carcasses from males had more breast meat than females. CONCLUSIONS AND ALICATIONS 1. A greater proportion of chicks from the prime flock (41 wk) emerged earlier from their eggs than from the young flock (32 wk). 2. After emergence, chicks being held in the hatcher up to 32 h reduced their BW and yolk sac reserves more than when held up to 6 h. 3. Despite losses from extended holding of early-emerging chicks in the hatcher, total live performance was similar to that of late-emerging chicks.

8 JOSEH AND MORAN: FLOCK AGE AND HATCH TIME Although live BW at 6 wk of age was similar for flock age, broilers from the prime flock had higher feed conversion during rearing and more abdominal fat than those from a young flock. 5. Yields of chilled carcass and breast meat were similar, regardless of chick source. 6. Males responded similarly to females with respect to hatchability and chick quality at hatch. At 6 wk of age, carcass and breast meat yields were higher for males than females. 1. Hager, J. E., and W. L. Beane osthatch incubation time and early growth of broiler chickens. oult. Sci. 62: Reis, L. H., L. T. Gama, and M. Chaveiro Soares Effects of short storage conditions and broiler breeder age on hatchability, hatching time, and chick weights. oult. Sci. 76: Williams, C., G. F. Godfrey, and R. B. Thompson The effect of rapidity of hatching on growth, egg production, mortality and sex ratios in the domestic fowl. oult. Sci. 30: Wyatt, C. L., W. D. Weaver, Jr., and W. L. 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M Inter-relationship between egg weight, parental age and embryonic development. Br. oult. Sci. 25: Yannakopoulos, A. L Lack of effect of oviposition time with parental age on chick weight when egg weight remains constant. Br. oult. Sci. 29: Suarez, M. E., H. R. Wilson, F. B. Mather, C. J. Wilcox, and B. N. Mcherson Effect of strain and age of the broiler breeder female on incubation time and chick weight. oult. Sci. 76: Christensen, V. L., J. L. Grimes, M. J. Wineland, and L. G. Bagley Effects of turkey breeder hen age, strain, and length of the incubation period on survival of embryos and hatchlings. J. Appl. oult. Res. 10: Natureform NMC-2000 (1,980-egg capacity), single-stage incubator, Natureform Hatchery Systems, Jacksonville, FL. 15. Romanoff, A. L Effects of different temperatures in the incubator on the prenatal and postnatal development of the chick. oult. Sci. 15: The experimental unit was the group of 15 eggs during incubation, the battery cage for chick quality data, and the floor pen for live performance and processing data. Eggs and birds from each treatment were blocked by location within the incubator and rearing facilities, respectively. During incubation, 2 baskets in the hatcher did not receive sufficient heat because of their distance from the heating coils. Hatchabilities in these baskets were 75 and 67% compared with approximately 82% for the other baskets. Based on these REFERENCES AND NOTES results, data from these 2 hatch baskets were eliminated from the data set. The data (excluding egg characterization analysis) were analyzed by 3-way analysis of variance using the GLM procedure in SAS [17]. To separate differences attributed to the egg versus those of the dam, egg characteristics were analyzed with egg weight as the covariate using the GLM procedure in SAS [17]. Hatch data were transformed to arc sine values before analysis. Differences between treatment means were separated using the Tukey s honestly significant difference test. Significance was based on testing at For flock age and hatch time, differences between males and females were not found and, therefore, will not be discussed further. 17. SAS Institute Inc The SAS System for Windows, Release SAS Institute Inc., Cary, NC, Cunningham, F. E., O. J. Cotterill, and E. M. Funk The effect of season and age of bird. 1. On egg size, quality, and yield. oult. Sci. 39: O Sullivan, N.., E. A. Dunnington, and. B. Siegel Relationships among age of dam, egg components, embryo lipid transfer, and hatchability of broiler breeder eggs. oult. Sci. 70: Burke, W. H Sex differences in incubation length and hatching weights of broiler chicks. oult. Sci. 71: Christensen, V. L., D. O. Noble, and K. E. Nestor Influence of selection for increased body weight, egg production, and shank width on the length of the incubation period of turkeys. oult. Sci. 79: Roland, D. A Recent developments in eggshell quality. Feedstuffs 48: Britton, W. M Shell membrane of eggs differing in shell quality from young and old hens. oult. Sci. 56: eebles, E. D., and J. T. Brake Eggshell quality and hatchability in broiler breeder eggs. oult. Sci. 66: Tullett, S. G., and R. G. Board Determinants of avian eggshell porosity. J. Zool. 183: Christensen, V. L., W. E. Donaldson, and J.. McMurtry hysiological differences in late embryos from turkey breeders at different ages. oult. Sci. 75: Mather, C. M., and K. F. Laughlin Storage of hatching eggs: the interaction between parental age and early embryonic development. Br. oult. Sci. 20: Noble, R. C., F. Lonsdale, K. Connor, and D. Brown Changes in lipid metabolism of the chick embryo with parental age. oult. Sci. 65: Applegate, T. J., D. Harper, and M. S. Lilburn Effect of hen production age on egg composition and embryo development in commercial ekin ducks. oult. Sci. 77: Applegate, T. J., J. J. Dibner, M. L. Kitchell, Z. Uni, and M. S. Lilburn Effect of turkey (Meleagridis gallopavo) breeder hen age and egg size on poult development. 2. Intestinal villus growth, enterocyte migration and proliferation of the turkey poult. Comp. Biochem. hysiol. B 124: Reinhart, B. S., and G. I. Hurnik Traits affecting the hatching performance of commercial chicken broiler eggs. oult. Sci. 63:

9 520 JAR: Research Report 32. Reinhart, B. S., and E. T. Moran, Jr Incubation characteristics of eggs from older small white turkeys with emphasis on the effects due to egg weight. oult. Sci. 58: Vick, S. V., J. Brake, and T. J. Walsh Relationship of incubation humidity and flock age to hatchability of broiler hatching eggs. oult. Sci. 72: Tona, K., E. Decuypere, and W. Coucke Effects of strain, hen age and transferring eggs from turning to stationary trays after 15 to 18 days of incubation. Br. oult. Sci. 42: Daly, K. R., and R. A. eterson The effect of age of breeder hens on residual yolk fat, and serum glucose and triglyceride concentrations of day-old broiler chicks. oult. Sci. 69: Godfrey, G. F., and R. G. Jaap Evidence of breed and sex differences in the weight of chicks hatched from eggs of similar weights. oult. Sci. 31: Zawalsky, M The effect of sex, egg weight and preincubation storage on hatching time and chick weight. oult. Sci. 41:1697. (Abstr.) 38. Khan, A. G., M. V. oulouse, and S. Chakraborte Sexual dimorphism in the weight of chicks. Br. oult. Sci. 16: Jull, M. A., and J.. Quinn The relationship between the weight of eggs and the weight of chicks according to sex. J. Agric. Res. 31: Morris, E. H., D. F. Hessels, and R. J. Bishop The relationship between hatching egg weight and subsequent performance of broiler chickens. Br. oult. Sci. 9: Marks, H. L Sexual dimorphism in early feed and water intake of broilers. oult. Sci. 64: Marks, H. L The role of water intake on sexual dimorphism for early growth of broilers. oult. Sci. 65: McNaughton, J. L., J. W. Deaton, F. N. Reece, and R. L. Haynes Effect of age of parents and hatching egg weight on broiler chick mortality. oult. Sci. 57: Tufft, L. S., and L. S. Jensen Effect of age of hen, egg weight, and sex on chick performance and lipid retention. oult. Sci. 70: Acknowledgments The authors thank Aviagen Incorporated for donation of eggs in kind as well as Derek Emmerson and Valerie Carney for their guidance. Also, assistance from Svetlana Blake, Jin Fung Chen, Jaume Galobart Cots, Angel Juarez Zarate, and graduate students at the oultry Science Unit was greatly appreciated.