Effects of photostimulatory lighting and feed allocation in female broiler breeders 1. Reproductive development

Effects of photostimulatory lighting and feed allocation in female broiler breeders 1. Reproductive development F. E. Robinson 1, R. A. Renema 1, L. Bouvier 1, J. J. R. Feddes 1, J. L. Wilson 2, M. Newcombe 3, and R. I. McKay 3 1 Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5, E-mail: frobinson@afns.ualberta.ca; 2 Department of Poultry Science, The University of Georgia, Athens, Georgia, 30602; 3 Shaver Poultry Breeding Farms Ltd., Cambridge, Ontario, Canada N1R 5V9. Received 24 February 1998, accepted 16 July 1998. Robinson, F. E., Renema, R. A., Bouvier, L., Feddes, J. J. R., Wilson, J. L., Newcombe, M. and McKay, R. I. 1998. Effects of photostimulatory lighting and feed allocation in female broiler breeders. 1. Reproductive development. Can. J. Anim. Sci. 78: 603 613. Changes in carcass traits during sexual maturation were studied with female Shaver Starbro breeders in a 2 2 factorial design with two lighting programs and two feeding programs. Pullets were individually caged in a light tight facility at 20 wk of age. The light period of fast photoperiod (FP) hens was changed from 8L:16D to 15L:9D at 20 wk of age. Slow photoperiod (SP) hens were switched from a 8L:16D photoperiod at 20 wk to 11L:13D, with increases to 12L:12D, 13L:11D, 14L:10D, and 15L:9D weekly to 24 wk of age. Slow feed (SF) hens were given small (5 g or less) weekly increases in feed allocation from 20 to 25 wk. Fast feed (FF) hens received larger feed allocations than the SF birds from 20 to 25 wk (maximum difference of 25 g more feed than SF hens received). Birds were processed at weekly intervals between 20 and 26 wk of age (Group A) or at sexual maturity (Group B), which was considered to be the day of the first oviposition. Age at sexual maturity did not differ due to photostimulation or feeding treatment. Whereas feeding program had no effect on carcass composition parameters at sexual maturity, the SP hens had a higher relative carcass lipid content at the expense of protein and ash content compared to FP hens. The weight of the large yellow ovarian follicles (LYF) at sexual maturity was affected by feeding regimen (FF, 50.2 g; SF, 43.6 g) and photoperiod (FP, 43.2 g; SP, 50.6 g). While hens on the SP photostimulation program had 8.9 LYF compared to 8.0 in FP hens at sexual maturity, the FF feeding regimen hens had 9.0 LYF compared to 7.9 in SF hens. The gradual feeding program of the SF treatment may be a potential means of limiting follicle recruitment and thereby potentially increasing settable egg production compared with feeding programs using more rapidly increasing feed allocations. Key words: Broiler breeders, photostimulation program, feed restriction, ovary morphology Robinson, F. E., Renema, R. A., Bouvier, L., Feddes, J. J. R., Wilson, J. L., Newcombe, M. et McKay, R. I. 1998. Effets d un éclairage photostimulateur et du rationnement des aliments chez les poules reproductrices de chair 1. Développement du système reproducteur. Can. J. Anim. Sci. 78: 603 613. Nous avons examiné, chez des reproductrices Shaver Starbro, l évolution des caractères de carcasse durant la maturation sexuelle, sous deux régimes d éclairage et deux régimes d alimentation. L expérience était conduite selon un dispositif factoriel 2 2. À l âge de 20 semaines, les poulettes étaient logées en cages individuelles dans un bâtiment complètement isolée de la lumière extérieure, sous un régime d éclairement de 8 h jour-16 h nuit. Dans le régime photopériodique accéléré (PA), la phase diurne d éclairement était allongée à 15 h dès la 20 e semaine. Dans le régime photopériodique lent (PL), la phase d éclairement passait de 8 à 11 h par jour à la 20 e semaine, pour ensuite s allonger de 1 h par semaine jusqu à la 24 e semaine (15 h). Dans le régime alimentaire lent (AL), la ration journalière des poulettes augmentait légèrement, soit de 5 g ou moins par semaine de la 20 e à la 25 e semaine. Dans le régime alimentaire accéléré (AA), la ration durant la même période était supérieure à celle des poulettes AL, avec un écart maximal de 25 g de plus par jour. Les poules étaient sacrifiées à intervalles d une semaine entre la 20 e et la 26 e semaine d âge (groupe A) ou à la maturité sexuelle (groupe B), coïncidant avec la date de la première ponte. L âge à la maturité sexuelle ne variait pas selon le régime d éclairement ou d alimentation. Alors que le régime alimentaire n avait pas d effet sur les paramètres de composition de la carcasse à la maturité sexuelle, les poules PL manifestaient une teneur en lipides de la carcasse relativement plus élevée par rapport aux teneurs en protéine et en cendres que les poules PA. Le poids des grands follicules ovariens jaunes (GFJ) à maturité sexuelle différait selon le régime d alimentation (AA:50,2 g; AL: 43,6 g) et la photopériode (PA: 43,2 g; PL: 50,6 g). À maturité sexuelle, les poules sous photopériode lente portaient 8,9 GFJ contre 8,0 pour celles sous régime PA, tandis que dans le régime alimentaire AA les poules en portaient 9,0 contre 7,9 pour les poules au régime AL. L accroissement graduel de l alimentation dans le régime AL serait un moyen éventuel de limiter le recrutement des follicules et ainsi d accroître la production d oeufs, par rapport à des programmes d alimentation accélérés. Mots clés: Reproductrices chair, programme photostimulateur, rationnement, morphologie ovarienne Broiler breeders are routinely feed restricted to circumvent the negative effects of excess body weight (BW) on ovarian follicular development and settable egg production. Feed 603 Abreviations: BW, body weight; FF, fast feed; FP, fast photoperiod; SF, slow feed; SP, slow photoperiod; LYF, large yellow ovarian follicles; POF, post-ovulatory follicles

604 CANADIAN JOURNAL OF ANIMAL SCIENCE restriction reduces frame size and lipid accretion (Yu et al. 1992a), and limits the number of preovulatory LYF on the ovary (Hocking et al. 1987; Yu et al. 1992b). Excess LYF are related to an increased incidence of multiple hierarchies (Hocking et al. 1989; Katanbaf et al. 1989), which is associated with increased production of unsettable eggs and a reduced rate of fertility and hatchability of eggs (Yu et al. 1992b). The BW of the bird at sexual maturity has been shown to be a primary indicator of the number of LYF (Hocking 1996). As the number and arrangement of LYF both influence settable egg production, an understanding of the factors that can alter the state of the ovary is desirable. Whereas the negative effects of ad libitum feeding broiler breeders have been well established, little literature is available on the effects of small differences in the degree of feed restriction during sexual maturation. Fattori et al. (1993) characterized the effects of small differences in dietary energy level commencing at 20 wk of age on BW and physical attributes associated with sexual maturity. An increased degree of feed restriction delayed sexual maturity in a dose-responsive manner, concurring with previous research (Wilson and Harms 1986; Robbins et al. 1988). Variability in the length of delays in sexual maturation is thought to relate to the degree of restriction or to lighting regimen variations (Robinson et al. 1993a). Poultry lighting experiments tend to focus on the timing of photostimulation (Hocking et al. 1988; Robinson et al. 1996) rather than the pattern of photostimulation. Currently, commercial broiler breeder pullets are typically photostimulated with a single increase in day length between 20 and 22 wk of age. Previous lighting trials performed without light-tight facilities have demonstrated seasonal effects on timing of sexual maturity and egg production (Morris and Fox 1960; Christmas and Harms 1982). In an early experiment, Morris and Fox (1960) reported that rearing birds on an artificial decreasing photoperiod followed by release to a naturally increasing photoperiod at 20 wk of age resulted in delayed sexual maturation and increased egg size, yet similar egg production to birds reared under naturally increasing day length conditions. A lower rate of lay for the treatment reaching sexual maturity earlier is typical of early photostimulated broiler breeders (Yuan et al. 1994; Robinson et al. 1996) and turkeys (Hocking et al. 1988). The use of a gradually increasing light period to photostimulate modern broiler breeders in a controlled, light-tight environment has not been investigated. The influences of a gradual or accelerated lighting program and feeding program from 20 to 25 wk of age on carcass traits and ovarian morphology were examined in broiler breeder females throughout this time period and at the point of sexual maturity (first oviposition). MATERIALS AND METHODS Stocks and Rearing Management A total of 600 Shaver Starbro 1 day-old broiler breeder pullets were reared in floor pens until 20 wk of age in a lighttight rearing facility. All pullets were allowed to eat ad libitum for the first 3 wk, after which they were feed restricted using skip-a-day feeding to control BW gains to the level recommended by the breeder. The birds were fed a starter diet for the first 3 wk (2875 kcal ME, 18% CP), followed by a grower diet until 20 wk (2700 kcal ME, 15% CP). Throughout the rearing period, drinking water was provided ad libitum. The photoperiod used during rearing was 24 h of light (24L:0D) for the first 4 d, followed by 8L:16D. All pullets were wing-banded at 4 wk of age. The experimental protocol was approved by the Faculty of Agriculture, Forestry and Home Economics of the University of Alberta s Animal Policy and Welfare Committee. Experimental Design At 20 wk of age the birds were weighed individually and the 356 birds closest to the 20-wk target BW were used in the study. These birds were randomly assigned to individual laying cages in a light-tight facility. Each cage was equipped with an individual feeder to allow individual feed allocations to be carried out with no feed being consumed by neighboring birds. The 356 birds were randomly assigned to one of three experimental fates as follows. A total of 140 pullets were euthanatized in seven subgroups of 20 birds each week between 20 and 26 wk of age (Group A). These birds were used to monitor weekly changes in carcass characteristics through the pubertal period. A further 72 birds were euthanatized on the day following their first oviposition to assess carcass characteristics and ovarian morphology at point-of-lay (Group B). The remaining 144 birds remained in laying cages to 64 wk of age to assess reproductive efficiency (Group C), the results of which are reported in a companion paper (Robinson et al. 1998). Beginning at 20 wk of age, the birds were exposed to one of two photostimulation programs and one of two feed allocation treatments in a 2 2 factorial experimental design as follows. The photostimulation treatments varied in the rate of increase from 8L:16D to 15L:9D. A SP program consisted of increasing the light period from 8L:16D at 20 wk to 11L:13D, followed by increases to 12L:12D (21 wk), 13L:11D (22 wk) 14L:10D (23 wk) and 15L:9D (24 wk) as shown in Fig. 1. The alternate FP consisted of a single step increase from 8L:16D at 20 wk to 15L:9D. Both photo regimens were housed in a common room, separated by a temporary light-tight wall with air recirculation ducts to maintain a common ambient temperature. When both photo regimens reached 15L:9D, this temporary wall was removed. The feeding programs differed in the rate of feed increases during the time period between 20 and 25 wk of age (Fig. 2). A SF regimen providing small incremental changes in feed allocation based on BW. If a feed increase of greater than 5 g was deemed necessary to obtain the desired BW gain, the change in feed allocation was divided up into two smaller increases during the week. A FF treatment was based on a more aggressive approach of increasing feed to breeder pullets. The original intent was to provide relatively large weekly increases in feed allocation during the 20- to 1 Shaver Poultry Breeding Farms Ltd., Box 400, Cambridge, ON, N1R 5V9

ROBINSON ET AL. REPRODUCTIVE DEVELOPMENT IN BROILER BREEDERS 605 Fig. 1. Histograms of the changes in daylight between 20 and 25 wk of age in the FP and SP photostimulation treatments. 25-wk period with a similar BW target to the SF birds at 25 wk of age. However, by 24 wk of age, it became apparent that the previous feed allocations may have been too generous, as assessed by pullet BW. Hence, the decision was made to reduce feed allocation by 10 g d 1 to keep the pullets close to the target BW. After 25 wk of age, the birds were fed a common feed allocation based on both BW and rate of lay. Fig. 2. Histograms of the changes in feed allocation between 20 and 25 wk of age in the FF and SF feeding program treatments. Carcass Parameters Assessed at Processing Birds processed at weekly intervals between 20 and 26 wk of age (Group A) or at the attainment of sexual maturity (first oviposition) (Group B), were weighed, blood sampled and euthanatized by cervical dislocation for necropsy to assess carcass and reproductive morphology. Group B birds were also weighed at first oviposition and all birds were deprived of feed for 16 h prior to processing. The length of the shank (tibiotarsus length between the top of the hock joint to the footpad) was recorded as an assessment of frame size. The weight of the breast muscle (pectoralis major and minor), liver, abdominal fatpad, oviduct, and ovary were recorded. The ovary was dissected, and the number of LYF (greater than 10 mm diameter) (if present) and individual LYF weights were recorded. If a hen had already ovulated that day, as determined by the presence of a yolk or a membranous egg in the oviduct, the largest ovarian follicle was recorded as being in the F2 (second largest) position. The weight of the stroma (ovarian tissue remaining after removal of LYF) was recorded. The number of post-ovulatory follicles (POF) on the stoma at processing was recorded. Unexplained POF, defined as ovulations occurring prior to the first oviposition, were calculated by subtracting prior ovipositions and eggs in the oviduct from the number of POF at processing as reported by Renema et al. (1995). All dissected organs, except for the livers, were returned to the respective carcasses. Carcasses were stored at 15 C and then subsequently thawed, pressure-cooked for 4 h, and homogenized in an industrial blender as described by Yu et al. (1990). Duplicate 150-g sub-samples were taken from the homogenate and freeze dried for 7 d and homogenized with a feed grinder. Corrections were made for moisture loss during carcass homogenization and freeze drying by monitoring changes in sample weight due to changes in water content throughout the procedures used. Portions of the freeze dried sample were analyzed in duplicate for determination of total carcass dry matter, crude protein, lipid, and ash using standard chemical analysis procedures of the Association of Official Analytical Chemists (1980). Livers were freeze dried, ground, and the total lipid content determined by petroleum ether extraction. Plasma lipid weight was determined using Folch lipid extraction. Chloroform was evaporated from the 15 ml extracted aliquot under a nitrogen stream on a hot-plate (70 C at surface) until a constant weight was achieved. Statistical Analysis The experimental design was a 2 2 factorial with main effects of photostimulation and feeding program. Birds within Group A and Group B were randomly assigned to cages. Data were subjected to two-way analysis of variance using the General Linear Models (GLM) procedures of SAS (SAS Institute, Inc. 1994). Parameters recorded for Group A birds in each group of birds processed between 20 and 26 wk of age were analyzed as individual groups to compare treatment effects at specific points. Data collected over time for Group B birds were analyzed for treatment effects as a single group. Sources of variation for data analysis within Group A and Group B birds were the photostimulation and feeding program main effects, as well as the interaction of the main effects. Only data for the main effects are presented for the birds processed each week (Group A). If the F-test was significant (P < 0.05), Duncan s multiple range test (Steel and Torrie 1980) was used to determine differences between means. The error variation for all variables consisted of bird variation within the interaction. Unless otherwise noted, all statements of significance were based on testing at the P < 0.05 level. RESULTS AND DISCUSSION Carcass and Ovarian Morphology During Sexual Maturation: Group A The BW profile of the Group A birds seen at processing in response to the photoperiod and feeding program main effects is presented in Fig. 3. Whereas there was no differ-

606 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 3. Processing BW and breast muscle weight of broiler breeders exposed to either a FP or a SP treatment (A) and a FF or a SF feeding regimen (B) beginning at 20 wk of age and processed at weekly intervals. ence in BW due to photostimulation program at any time, at 22 wk of age birds on the FF regimen weighed more than those on the SF regimen. This BW difference carried through to birds processed at 23 wk of age. At 26 wk of age, the birds processed from the FF regimen were also significantly heavier than SF birds, although the difference was not as great as for birds processed at 22 and 23 wk of age. This indicated that the reduction in feed allocation at 24 wk of age was effective in making BW in the two feeding regimens more similar by 26 wk of age. Changes in breast muscle weight followed a similar pattern to changes in BW in time. The breast muscle weight of FF birds was similar to that of SF birds processed at all ages prior to 26 wk of age, when the FF breast muscle weight was greater (Fig. 3). Whereas this corresponds with the BW difference at this time, FF breast muscle weights were not different from those of SF birds at 22 and 23 wk, when there were BW differences. Breast muscle weights due to the photostimulation treatment were similar (Fig. 3), although the weight of the SP bird breast muscle was greater than that of the FP birds at 25 wk of age. Photostimulation treatment did not appear to affect breast muscle weight in a predictable manner. The weight of the abdominal fatpad was not significantly affected by photostimulation program, but was increased in birds on the FF feeding regimen and processed at 23, 24, or 25 wk of age (Fig. 4). The accelerated feeding program of FF birds appeared to have supplied surplus nutrients, enabling the greater abdominal fatpad size in FF birds than in SF birds at these ages. The greatest difference in abdominal fatpad weight between feeding regimens occurred at 23 wk of age (20.1 g), following which the weights became more similar until 26 wk of age, when abdominal fatpad weights of FF and SF birds processed were not different. The abdominal fatpad weights of FF and SF birds through time were similar to those reported by Fattori et al. (1993) for their standard and 8% (kcal kg 1 ) dietary treatments. As with the current experiment, Fattori et al. (1993) found a significantly greater fatpad weight at 24 wk of age in birds receiving a greater amount of nutrients. The similarity of breast muscle weights (Fig. 3) and carcass protein contents (data not shown) between FF and SF birds suggests that lean tissue growth was substantially altered by feeding treatments. The reduced abdominal fatpad size observed in SF compared to FF birds in birds processed between 23 and 25 wk of age (Fig. 4) indicates

ROBINSON ET AL. REPRODUCTIVE DEVELOPMENT IN BROILER BREEDERS 607 Fig. 4. Abdominal fatpad weight, relative carcass lipid content, and liver weight of broiler breeders exposed to either a FP or a SP treatment (A) and a FFor a SF feeding regimen (B) beginning at 20 wk of age and processed at weekly intervals. the primary difference in body composition between FF and SF birds was lipid content. However, carcass lipid content did not significantly differ in any time period for either photostimulation or feeding program treatments (Fig. 4). The similar pattern of the carcass lipid and abdominal fatpad weight curves for the FF and SF birds suggest that differences observed in fatpad weight were indicative of a more systemic difference in lipid content in which feeding differences were not yet substantial enough to significantly affect lipid deposition beyond the abdominal fatpad.

608 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 5. Oviduct weight of broiler breeders exposed to either a FP or a SP treatment (A) and a FF or a SF feeding regimen (B) beginning at 20 wk of age and processed at weekly intervals. Liver weight was not affected by photostimulation treatment, but was significantly greater in birds on the FF feeding regimen than the SF regimen and processed at 22, 23, or 24 wk of age (Fig. 4). The liver can respond quickly to changes in feeding level and metabolic status as indicated by changes in its weight and lipid content. Robinson et al. (1993b) reported that following 1 wk of ad libitum feeding broiler breeder hens at 44 wk of age, the absolute liver weight and lipid content increased by 2.7-fold and 16-fold, respectively, and significant increases in abdominal fatpad weight were observed following two weeks of ad libitum feeding. In the current study, the mean liver weight of FF birds processed between 22 and 24 wk of age was 21.4% higher than in SF birds. Following the reduction in feed allocation to FF birds at 24 wk of age, liver weights of FF birds were only 6.2% greater than in SF birds on average (weeks 25 and 26), which was not significantly different. The relative liver lipid content of FF birds was greater than in SF birds processed at 23 wk of age (13.0% vs. 7.1%, respectively). Relative liver lipid content increased in the flock from a low of 6% in birds processed prior to 22 wk of age to 16% in birds processed between 22 and 24 wk of age (data not shown). As the mean age of first oviposition (sexual maturity) was 24.3 wk of age (170 d), the apparent 267% increase in relative liver lipid content in the time interval between the processing of these groups may have been due to increased lipid requirements needed to maintain an active ovary. The higher relative liver lipid content of the FF birds processed at 23 wk suggests that the more generous feeding program of these birds may have allowed a more rapid initiation of ovarian large follicle development. Alternatively, the high liver lipid content may be an indicator of the elevated rates of lipid deposition observed to sites such as the abdominal fatpad (Fig. 4) which coincided with ovarian development in FF birds. The photoperiod treatments did not affect the apparent rate of oviduct development (Fig. 5), or the ovary characteristics (Fig. 6). However, at 23 wk of age the birds on the FF feeding program had heavier oviducts, ovaries, and more LYF than did SF birds. This suggests that the elevated relative liver lipid content observed in FF compared to SF birds at 23 wk may have been indicative of either an accelerated rate of reproductive development in FF birds or a reduced rate of development in SF birds at this age. As the ovarian stroma weight was only numerically greater in FF than in SF birds at 23 wk, the greater FF ovary weight at this time was due to a greater number of LYF. Beginning with birds processed at 23 wk of age, the oviduct weight and ovarian parameters of FF birds were consistently higher than those of SF birds, although by 24 wk of age these differences were only numerical. The BW difference between FF and SF birds was greatest when compared at 23 wk (Fig. 3), corresponding with many of the differences observed in the reproductive organs. Fattori et al. (1991) noted a negative correlation between BW and age at sexual maturity, which indicated a more advanced rate of sexual development in heavier birds, concurring with the results of the current study near 23 wk of age. This early difference in reproductive development would be expected to relate to an early sexual maturation in FF birds, or, conversely, to a delayed sexual maturity in SF birds. Carcass Morphology at Sexual Maturity: Group B Despite apparent differences in rate of sexual maturation observed in FF compared to SF birds processed at 23 wk of age, there was no difference in the timing of sexual maturation in birds on the FF and SF feeding regimens, or in the FP and SP lighting scheme (Table 1). This is unlike the result reported for the more numerous C-birds (Robinson et al. 1998), where both the SF feeding regimen and the SP lighting program were reported to reach sexual maturity later than their counterparts. In the current study, feeding program did not significantly affect body weight at sexual maturity under the FP lighting scheme. However, under the SP lighting scheme, SP-FF hens entered lay weighing 6.0% more than their SP-SF photoperiod counterparts and 8.2% more than their FP-FF feeding program counterparts. Shank length, breast muscle weight, abdominal fatpad weight, liver weight or lipid content, and plasma lipid content were not different for the photostimulation or feeding programs and

ROBINSON ET AL. REPRODUCTIVE DEVELOPMENT IN BROILER BREEDERS 609 Fig. 6. Ovary weight, stroma weight, and number of LYF of broiler breeders exposed to either a FP or a SP treatment (A) and a FF or a SF feeding regimen (B) beginning at 20 wk of age and processed at weekly intervals. their interaction. The relative breast muscle weight, however, was greater in SF birds of the SP photostimulation program than in SP-FF birds. This difference was due to the smaller SP-SF birds having a similar absolute breast muscle mass to the larger SP-FF birds, with breast muscle then representing a larger proportion of their BW. There was a photostimulation effect on relative breast muscle weight in the SF birds that did not relate to BW differences, where SP-SF birds had a higher proportion of breast muscle than their FP- SF counterparts.

610 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 1. Age, BW, shank length, breast muscle weight, abdominal fatpad weight, liver weight and relative lipid content, and plasma lipid content of broiler breeders at sexual maturity following exposure to either a FP or a SP treatment and a FF or a SF feeding regimen from photostimulation (20 wk of age) Age at first BW at Breast muscle Abdominal fat pad Liver Liver lipid Plasma lipid egg first egg z weight weight weight content content Source (d) (g) (g) (%) (g) (%) (g) (%) (%) Photostimulation program Fast (FP) 169.6 2636 387 14.7 87.6 3.4 42.4 13.8 2.11 Slow (SP) 170.5 2714 402 14.8 82.7 3.0 43.4 14.9 1.83 SEM 1.2 32 7 0.2 10.7 0.4 1.0 0.9 0.23 Feeding program Fast (FF) 169.0 2687 396 14.7 94.7 3.6 43.5 14.5 1.82 Slow (SF) 171.1 2662 393 14.8 75.6 2.8 42.3 14.1 2.12 SEM 1.2 32 7 0.2 10.7 0.4 1.0 0.9 0.23 Interactions FP-FF 169.8 2582b 389 15.1ab 97.7 3.9 42.4 14.8 1.92 FP-SF 169.3 2690ab 385 14.3b 77.4 2.9 42.5 12.8 2.31 SP-FF 172.3 2793a 403 14.4b 91.6 3.3 44.6 14.3 1.73 SP-SF 168.7 2635b 401 15.2a 73.8 2.8 42.1 15.5 1.94 SEM 1.7 45 11 0.3 15.3 0.6 1.5 1.3 0.32 z Processing BW following 12 h feed withdrawal. a b Means within a column and within a source with no common letter differ significantly. The absolute weights of all carcass composition parameters were similar for all treatments at sexual maturity, with the exception of carcass lipid weight in the photostimulation treatments. Carcass lipid content of FP birds was 379 g compared to 406 g in SP birds. This difference was reflected in the relative carcass composition measures (Table 2), where SP bird carcasses contained 15.9% lipid compared with 15.2% for FP birds. The higher proportion of lipid in SP birds may have contributed to their significantly reduced relative carcass protein and ash contents compared with FP bird values. The treatment interaction means indicate these observations were limited to the FF feeding regimen, where the carcass lipid content of the SP-FF birds was 16.5% compared with 14.3% in FP-FF birds, and relative carcass protein, ash, and water contents were lower in the SP-FF birds. The carcass lipid content of overfed birds has been reported to be larger than that of feed restricted controls primarily at the expense of water (Yu et al. 1992a). In the current study, the limiting of carcass composition differences to the photostimulation programs within the FF feeding program suggests a potential relationship between photostimulation program and carcass composition under conditions of excess nutrient availability. Feeding program affected carcass composition differently under the FP and SP lighting regimes (Table 2). The larger SP-FF birds had a higher relative carcass lipid content and a lower ash content than SF birds on the SP photostimulation program. The opposite effect was observed within FP birds, where SF birds had a higher relative carcass lipid content and a lower ash content than FF birds. These opposing observations within the interaction contribute to the lack of differences within the feeding program main effect. Relative carcass lipid content relates well to BW at sexual maturity, as the heaviest (SP-FF) and lightest (FP-FF) birds at this time also contained the highest and lowest proportion of lipid, respectively. Reproductive Morphology at Sexual Maturity: Group B The weight of the oviduct at sexual maturity was not affected by photostimulation or feeding program (Table 3). Mean oviduct weight was 54.3 g, which was lower than the 66 g reported by Goerzen (1996) and the 63 g by Robinson et al. (1996). The mean number of unexplained POF on the ovary at sexual maturity in the current study was 3.5 and was also not effected by treatment. In a recent study of male-line and female-line turkey hens, Melnychuk et al. (1997) reported the presence of 3.4 and 1.2 unexplained POF, respectively. The higher incidence of unexplained POF in the more growth-selected male-line hens was suspected to be due to a reduced rate of oviduct maturation relative to ovary development, resulting in the loss of potential eggs due to oviduct incompetence. Incidence of unexplained POF in the broiler breeders of the current study were comparable to that of the male-line turkeys of Melnychuk et al. (1997). Ovary morphology was highly influenced by both the photoperiod and feeding program treatments (Table 3). The ovaries of SP treatment birds were 12.5% heavier than those of FP birds. As ovarian stroma weight was similar between photostimulation groups, this weight difference was due to a significantly greater yolk mass on SP bird ovaries. The difference in yolk mass was associated with the number of LYF, with the ovaries of SP birds having 8.9 LYF compared with 8.0 LYF in FP birds (P = 0.04). The increased yolk mass and LYF number in SP birds indicates a greater stimulatory role of the gradually increasing photoperiod than the single, sudden increase in daylength of the FP program. A possible explanation is that the SP birds were being re-photostimulated weekly with each increase in light period. This would result in five partial photostimulations compared with one large one in the FP treatment, which could allow increased production of follicle stimulating hormone and luteinizing hormone from the anterior pituitary, resulting in

ROBINSON ET AL. REPRODUCTIVE DEVELOPMENT IN BROILER BREEDERS 611 Table 2. Relative water, protein, lipid, and ash contents of broiler breeders at sexual maturity following exposure to either a FP or a SP treatment and a FF or a SF feeding regimen from photostimulation (20 wk of age) Carcass Carcass Carcass Carcass water content protein content fat content ash content Source (%) (%) (%) (%) Photostimulation program Fast (FP) 60.3 20.5a 15.1b 3.65a Slow (SP) 59.7 20.2b 15.9a 3.50b SEM 0.3 0.1 0.3 0.04 Feeding program Fast (FF) 60.0 20.4 15.4 3.56 Slow (SF) 60.0 20.3 15.6 3.59 SEM 0.3 0.1 0.3 0.04 Interactions FP-FF 60.8a 20.7a 14.3c 3.74a FP-SF 59.8ab 20.4ab 16.0ab 3.57b SP-FF 59.2b 20.0b 16.5a 3.39c SP-SF 60.3ab 20.3ab 15.3bc 3.61ab SEM 0.4 0.1 0.4 0.06 a c Means within a column and within a source with no common letter differ significantly. Table 3. Oviduct, ovary, and total LYF weights, number of LYF, percentage of LYF in multiple sets, and number of unexplained POF of broiler breeders at sexual maturity following exposure to either a FP or a SP treatment and a FF or a SF feeding regimen from photostimulation (20 wk of age) Oviduct Ovary Ovarian stroma Total LYF Number % LYF in Unexplained weight weight weight weight z of LYF multiple sets y POF x Source (g) (g) (g) (g) (#) (%) (#) Photostimulation program Fast (FP) 54.5 51.1b 7.86 43.2b 8.04b 58.9 3.5 Slow (SP) 54.1 57.5a 6.89 50.6a 8.87a 61.4 3.4 SEM 1.4 2.3 0.38 2.1 0.27 4.4 0.2 Feeding program Fast (FF) 55.6 57.5a 7.33 50.2a 9.03a 60.6 3.5 Slow (SF) 53.1 51.1b 7.43 43.6b 7.88b 60.0 3.5 SEM 1.4 2.3 0.38 2.1 0.27 4.4 0.2 Interactions FP-FF 55.8 54.0 7.51 46.4 8.59 58.4 3.2 FP-SF 53.2 48.1 8.21 39.9 7.50 59.4 3.9 SP-FF 55.3 61.0 7.14 53.9 9.47 62.9 3.8 SP-SF 52.9 54.0 6.64 47.4 8.27 59.9 3.1 SEM 1.9 3.2 0.54 2.9 0.38 6.3 0.3 z Total weight of LYF (>10 mm diameter). y LYF arranged in groups differing by < 1 g. x Post-ovulatory follicles not accounted for by eggs laid and by yolks or eggs in the oviduct. a b Means within a column and within a source with no common letter differ significantly. increased ovarian follicle production and estrogen secretion. Increased plasma estrogen is known to stimulate hepatic fatty acid synthesis and the formation of phospholipids and proteins to package lipid particles for yolk deposition (Walzem 1996), thereby increasing both yolk deposition and LYF mass. The FF feeding program caused significant increase in both ovary weight and total LYF weight compared to SF birds (Table 3). The greater ovary weight in FF birds was associated with a significant 1.1 follicle increase in LYF number compared to the SF bird value (P = 0.004). The relatively minor difference in the feeding programs of the current study affected both large follicle recruitment and total yolk deposition. Previous work with overfeeding broiler breeders near sexual maturity has demonstrated increased numbers of LYF, which tend to be arranged in multiple follicle hierarchies (Hocking et al. 1989; Katanbaf et al. 1989; Yu et al. 1992b). Excess LYF production is associated with increased unsettable egg production and reduced fertility. Body weight is considered to be the primary effector of LYF numbers, with higher LYF numbers being associated with treatment groups or strains with greater BW (Hocking 1993). As BW did not differ between FF and SF birds in the current study, feeding level during sexual maturation is possibly the primary effector of LYF number. Hocking (1993) reported that the LYF numbers of broiler breeder hens weighing the same at sexual maturity were related to their feeding level in the preceding time period. However, the effect of feeding level on LYF number was reported to be less than that of BW. The 0.9 follicle (photostimulation treatment) to 1.1 follicle (feeding program) increase in LYF numbers in the current study is considerably larger than the

612 CANADIAN JOURNAL OF ANIMAL SCIENCE mean increase of 0.4 follicles reported by Hocking (1993) for treatments with similar variation in feeding levels to those reported in the current study. Based on these previous studies, the FP photostimulation treatment birds and the SF feeding treatment birds, which both had fewer LYF than their treatment counterparts, would both be expected to have higher rates of settable egg production than the SP and FF birds, respectively. Whereas the egg production of SF birds in a companion study was 10.9 eggs greater than that of FF birds, the superior laying patterns of FP compared to SP hens early in lay appeared to be transient, and ultimately chick production was higher in the SP treatment (Robinson et al. 1998). Goerzen (1996) reported LYF numbers at sexual maturity in birds reared on high, standard, or low growth curves to range from a high of 7.8 to a low of 6.8. Although these data were not statistically significant (P = 0.08), there were a significantly greater proportion of LYF grouped as multiple follicle sets (follicles within 1 g of each other) in birds on the high growth curve (48.2%) compared with the low growth curve (22.8%). In the current study there was no difference in multiple follicle arrangement of LYF due to photoperiod or feeding treatment (Table 3). Whereas there were significant differences in the number of LYF between treatments, this was not reflected in the follicle arrangement. A mean value of 60.1% of LYF in all treatments were in a multiple follicle arrangement. As the mean LYF number in the current study was 8.5 compared with 7.3 in the study reported by Goerzen (1996), it is not surprising that the overall incidence of multiple follicle was also greater. Hocking (1996) reported the proportion of LYF (>8 mm diameter) in multiple follicle sets to be 53% and 34% for birds with 9.2 and 7.6 LYF, respectively. CONCLUSIONS These data have characterized the effects of a sudden, compared with a gradual, photostimulation and feeding program on carcass and ovarian morphology during sexual maturation. Whereas the long-term effects of these differences are examined elsewhere (Robinson et al. 1998), this experiment demonstrated the primary effects of the experimental treatments to be on ovary mass and morphology. Although carcass and reproductive measurements of Group A birds processed at 23 wk of age indicate that birds on the FF feeding program may have been sexually maturing at a faster rate than SF birds, this did not result in significantly different carcass traits in Group B birds processed at sexual maturity. Within the FF feeding regimen, birds on the FP photostimulation program had a greater lipid content than those on the SP program. The smaller ovary weight of FF- FP birds compared with FF-SP birds may indicate an effect of photostimulation program on lipid allocation to the ovary compared to carcass stores under FF feeding conditions. Comparison of the Group A carcass trait profiles with the Group B birds at the mean day of sexual maturity (24.3 wk of age) reveals comparable results. This consistency demonstrates the reliability of data collected from birds processed weekly for the prediction of flock body composition at a particular age. Photostimulation treatment altered carcass composition at sexual maturity, with the fatter SP birds having a 0.9 increase in LYF number compared to FP birds. Birds on the FF feeding regimen had 1.1 more LYF than birds on the SF regimen despite the similarities of these birds for all carcass traits other than the ovary. The treatments resulting in fewer LYF at sexual maturity would be expected to have better settable egg production due to the association of excess LYF production with unsettable eggs. These results demonstrate an effective method (SF) for potentially refining the limitations placed on excess ovarian follicular recruitment by feed restriction programs, thereby allowing a more orderly cooperation between the ovary and the oviduct for the production of settable eggs. The gradual photostimulation pattern of the SP photostimulation program may be repeatedly stimulating the bird. The production of an additional LYF in the SP compared to the FP photostimulation treatment did not reduce settable egg production (Robinson et al. 1998), meaning that this method of bringing birds into production may have application with strains that are difficult to photostimulate. 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