Sexual differentiation of the photoperiodic response in Japanese quail

Plasma levels of LH are generally higher in male than in female quail. This dimorphism was found to persist in quail which had been through a breeding cycle and then gonadectomized. Under long daylengths (12 h light : 12 h darkness (12L : 12D) or 16L : 8D) ovariectomized quail had plasma levels of LH that were 55-70% of those seen in castrated birds. The difference was reduced after transfer to short days (8L : 16D) when LH concentrations fell to basal levels, but again became more pronounced when the quail were restimulated with long photoperiods. Thus, the photoperiodic response system is sexually differentiated.