Reproductive efficiency and metabolism of female broiler breeders as affected by genotype, feed allocation, and age at photostimulation. 2. Sexual maturation

A 3 x 4 x 2 factorial design trial was conducted to determine the effect of 3 broiler breeder strains, 4 target BW profiles, and 2 photostimulation ages on sexual maturation traits. A total of 560 pullets from each strain (Hubbard Hi-Y, Ross 508, and Ross 708) were housed in 24 pens. The BW profiles diverged at 4 wk and subsequently converged. at 32 wk of age as follows: standard (approximate mean target BW profile of the 3 strains), low (12-wk BW target = 25% lower than standard followed by rapid gain to 32 wk), moderate (12-wk BW target = 150%, of standard followed by lower rate of gain to 32 wk), and high (12-wk BW target = 200% of standard followed by minimal growth to 32 wk). Birds were photostimulated. at 18 (18WK) or 22 (22WK) wk. Eight birds per interaction (n = 192) were killed and dissected at sexual maturity (first oviposition). Body weight profile affected timing of sexual maturity with the 18WK but not the 22WK treatment. There was no effect of BW profile on initial egg weight. Mean BW at sexual maturity was 3.40, 3.21, 3.01, and 2.84 kg for high, moderate, standard, and low birds, respectively. This affected shank and keel length, indicating differences in frame size. Ovary weight at sexual maturity was 6 g heavier in the low treatment (55 g) compared with other BW profiles. This was related to recent feeding level, which was highest at sexual maturity in the low treatment. Arrangement of ovarian large yellow follicles (LYF) changed with photostimulation age. Birds that were photostimulated at 18WK had 1.33 LYF hierarchies, compared with 1.22 in 22WK birds. The 18WK-high birds had increased excess LYF production (55% paired) compared with other BW profiles, whereas both small yellow follicle number and atresia were increased. Feeding profiles affected growth and conformational traits, with little effect on reproductive morphology at sexual maturity.