| dc.description.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. | en_US |
