Reproduction and Photoperiods

Reproductive processes in all female birds are subject to regulation by changes in photoperi­ods (period of light exposure per day). Increas­ing periods of light, such as during the spring, induce hormonal changes in wild female birds to initiate egg production and mating behavior.

Breeds of domestic chickens selected for high egg production will begin egg laying if they reach maturity during either spring (increasing day length) or fall (decreasing day length). However, chickens raised during the spring reach maturity and begin laying at earlier ages. Egg size is reduced when smaller, younger chickens begin laying, so producers often manipulate photoperiods to delay the beginning of laying until birds are of an appropriate size. After laying has begun, reductions in photoperiods will lower egg production, as compared to egg produc­tion with a constant photoperiod.

Increasing periods of light are associated with testicular enlargement and development in birds that are seasonal breeders. Male domes­tic chickens (roosters) will reach sexual matu­rity and begin spermatogenesis when raised with either a long photoperiod (14 or more hours of light per day) or a short photoperiod (such as 8 hours per day). However, spermato­genesis is delayed with shortened photoperi­ods. The beginning of spermatogenesis is associated with increasing levels of FSH and LH. Mature males must be maintained with appropriate photoperiods for maximal fertility.