Reproductive efficiency and metabolism of female broiler breeders as affected by genotype, feed allocation, and age at photostimulation. 3. Reproductive efficiency

A 3 x 4 x 2 factorial trial was performed to test the effect of 3 broiler breeder strains, 4 target BW profiles, and 2 photostimulation ages on egg and chick production. Hubbard Hi-Y, Ross 508, and Ross 708 pullets were reared on BW profiles that separated at 4 wk and converged at 32 wk: standard (approximate mean target BW profile of the 3 strains used), 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 (12wk BW target = 200% of standard followed by minimal growth to 32 wk). Birds were photostimulated at 18 (18WK) or 22 wk (22WK). Twelve birds per interaction (n = 288) were individually caged at 17 wk and monitored for egg and chick production to 58 wk of age. The low BW profile delayed onset of lay, particularly in 18WK hens. Low and standard birds had a greater initial egg weight than moderate birds. The 18WK photostimulation age resulted in production of 31 small eggs (< 52 g) compared with 15 in 22-wk birds. A settable (52 g) egg weight was reached earliest by standard birds (187 d of age). Average prime sequence length was reduced by 7.0 eggs in moderate and high birds compared with other profiles. The 18WK hens laid 9 more eggs (174) than 22WK birds, with no effect on unsettable eggs. The 22WK birds laid 7 more settable eggs due to increased early egg size. Total egg output was similar among BW profile treatments, although Ross 708-high hens under-performed compared with the other 708 profiles. The Ross 508-high birds laid the same number of eggs as Ross 508-standard birds (mean = 178.7). Feeding profiles affected egg production traits differently among strains. Feed intake had more effect on egg Size and early production traits than BW profile or BW.