Abrupt or gradual increases in photoperiod for broiler breeders

Cobb 500 broiler breeder females (n = 832), which had been raised to achieve a typical 20-week body weight of 2.1 kg, were subjected to an abrupt or gradual increase in photoperiod to determine the effects on reproductive performance. One group (n = 416) was reared on 8-h photoperiods till 19 weeks and abruptly transferred to 16-h photoperiods. Another group (n = 416) was reared on 8-h photoperiods and given an initial increase to 12 h at 19 weeks, then weekly increments of 1 h to reach 16 h at 23 weeks. Both groups were reared in light-proofed facilities to 23 weeks and then moved to curtain-sided housing and maintained on 16-h daylengths to 60 weeks. There were no significant differences between the two lighting groups for age at sexual maturity, total egg production, egg mass output, mean egg weight to or body weight at 60 weeks. However, the birds given a single abrupt increment had a higher peak rate of lay whilst those given a gradual increase in daylength had better egg production at the end of the laying cycle. Broiler breeders transferred from closed rearing to curtain-sided adult accommodation (similar to that in which a large proportion of broiler breeders are housed) respond similarly to abrupt and gradual increases in daylength as do birds maintained throughout in controlled environment accommodation, and modern genotypes have similar responses to early genotypes. _______________________________________________________________________________________