Reproductive status in broiler breeder males is minimally affected by a mid-cycle increase in photoperiod.

1. Broiler breeder males were reared on 8-h photoperiods, transferred to 12 h at 20 weeks, and either maintained on 12 h or further transferred to 14, 16, 18, 20 or 22 h at 40 weeks to determine whether reproductive status and the timing of the onset of adult photorefractoriness is influenced by photoperiod during the breeding cycle. 2. No photoperiodic effect was observed on sperm concentration although the combination of large variation within a treatment and the lack of a semen sample from some males at each collection may have masked small differences and indicates that perhaps fertility in individual males fluctuates naturally during the breeding season. 3. The rate of comb growth to, and testicular weights at, 60 weeks were not significantly different between treatments. 4. Plasma testosterone concentration at 60 weeks of age declined linearly with photoperiod between 12 and 22 h, suggesting that in the birds exposed to the more stimulatory photoperiods after 40 weeks, hypothalamic-pituitary-gonadal activity shut down earlier. 5. An increase in photoperiod at 40 weeks of age appears to advance the onset of photorefractoriness in male broiler breeders, evident from the decline in testosterone concentration with increasing photoperiod; it is however insufficient to affect sperm concentration or comb area.