Impact of Feeding Regimens on Reproductive Development and Performance in Female and Male Broiler Breeders

Abstract

Rising global demands for poultry meat, coupled with chick shortages in the broiler industry, have placed increasing pressure on primary breeders to improve the reproductive performance of broiler breeders. Decades of intense genetic selection for rapid growth in broilers have resulted in parent stock with the same elevated growth potential, creating management challenges to ensure proper body weight (BW) targets are met for reproduction, as growth and reproduction are negatively correlated. To manage this negative relationship, the industry relies on the implementation of feed restriction regimens, which have proven useful for limiting excessive growth. However, such methods, especially as restrictions have become more severe, have been shown to disrupt normal metabolic function, impair reproduction, and raise welfare concerns, highlighting the need for further investigation. Therefore, this thesis investigated how feeding regimens (FR) could impact the BW, tissue development, and reproductive performance of both female and male broiler breeders separately. At 3 woa, 216 Cobb 500 FF females and 144 Cobb males were individually caged and pre- assigned one of three FR: (1) daily-fed standard diet (ED), (2) skip-a-day standard diet (SKIP), or (3) daily-fed high-fiber diet (HF). FR were initiated at 4 woa, and birds received individual allocations corrected for weekly energy intake. SKIP birds transitioned to a daily allocation at 17 woa, while HF continued for the remainder of the study. All individuals, regardless of sex, were weighed on a weekly basis. For females, daily egg production was recorded, and egg quality was assessed weekly to peak production (30 woa) and then at 5 week increments thereafter. For males, semen collection was performed weekly beginning at 24 woa with sperm concentration and mobility assessed. Male fleshing and comb scores were also recorded at 18 woa and then every 10 weeks from 30-60 woa, while wattle size was measured at the same intervals from 30-60 woa. Throughout the study, a subset of birds was euthanized (n=6/treatment/timepoint) via cervical dislocation for tissue collection at 6, 12, 20, 22, 23, 26, 30, 35, 50, and 55 woa. Sampling timepoints from 6 to 22 woa were performed on both sexes, while sampling at 23, 30, and 50 woa were only performed on females, and 26, 35, and 55 woa were only performed on males. The abdominal fat pad, liver, and sex specific gonads, such as the ovary and oviduct for females, and the right testes (RT) and left testes (LT), were weighed for males. Shank length was also recorded. In females, HF birds exhibited the steepest growth trajectory, followed by ED, while SKIP birds showed delayed growth and age of first egg (AFE), likely due to intermittent feeding, with signs of metabolic disruption such as increased relative liver weight in early lay. ED and HF birds reached AFE earlier and achieved higher egg weights and production rates at younger ages. Although cumulative egg numbers did not differ significantly, numerical trends suggest potential economic implications, with HF hens showing a reproductive advantage. Eggshell thickness (EST) was highest in HF hens, while settable egg production was lowest in early and late lay across FR. In males, age, treatment, and their interaction affected BW (P<0.001), with HF and ED males heavier than SKIP males during rearing and throughout sexual maturation. HF males exhibited higher fleshing scores than SKIP at 18 woa (P = 0.003) and larger combs overall (P=0.007), suggesting enhanced nutrient portioning toward lean tissue and secondary sex characteristics. Sperm concentration and mobility increased with age (P < 0.001), peaking at 31 woa, while ED males produced semen more consistently than SKIP males (P = 0.003). A BW threshold for semen production was identified; males weighing 2.6 kg had a 93% probability of producing, while those at 4.2 kg have a 98.6% probability. No upper BW limit was established. Tissue analysis revealed FR effects on abdominal fat pad (P < 0.001), liver weight (P = 0.002), and testes weight (P = 0.004), with HF and ED males exhibiting larger testes than SKIP males. HF males also had longer shanks than ED males, likely due to fiber-enhanced nutrient utilization. Collectively, these findings demonstrate that nutrient delivery method, even under equal energy intake, influences growth trajectory, metabolic traits, and reproductive development in broiler breeders. Further research is needed to clarify the metabolic pathways linking FR, energy utilization, and reproductive outcomes.