Effect of final photoperiod and twenty-week body weight on sexual maturity and early egg production in broiler breeders

Cobb broiler breeder pullets, grown to achieve 2.19 kg (normal growth) or 2.41 kg (faster growth) BW at 20 wk, were given continuous light during the first 2 d posthatch, were reared on 8-h photoperiods between 2 d and 20 wk of age, and were then transferred abruptly to 10-, 11-, 12-, 14-, 16-, or 18-h photoperiods at 20 wk. Controls remained on 8 h at 20 wk. The birds were reared on a litter-floor from 1 d and transferred at 15 wk to individual cages. Mean age at first egg (AFE) was advanced by 12 d, compared with controls, for the transfer to 10 h, and progressively earlier for longer photoperiods until a 25-d advance for 14 h; AFE was similar for pullets transferred to 14, 16, and 18 h. A quadratic regression indicated that a transfer to 15 h would induce the earliest maturity. On average, accelerating growth by about 10 d advanced AFE by 4 d, but the difference was larger for transfers to a more stimulatory photoperiod. Body weight at first egg increased by about 20 g for each 1-d delay in first egg and was 110 g heavier for the faster growth pullets than for controls. Egg numbers to 39 wk increased by 0.75 for each 1-d earlier AFE. Mean egg weight was negatively related to photoperiod, decreasing by 0.3 g per 1-h, but positively linked to AFE, increasing by 0.1 g for each 1-d delay in AFE. Faster growth did not significantly increase egg numbers or mean egg weight, but it did increase egg output to 39 wk by 150 g. The data suggest that broiler breeders reared on 8-h daylengths do not need more than a 14-h photoperiod in the laying period to optimize sexual development or egg production. Typically recommended BW targets for broiler breeders (2.1 to 2.2 kg) appear to be optimal for egg production. Responses to the lighting treatments were independent of those to 20-wk BW.