“…In the majority of birds that have been studied, when photoperiod reaches a critical threshold in the spring (usually 12 h of light or more, termed long days), production and secretion of the hypothalamic decapeptide chicken gonadotropin-releasing hormone I (cGnRH-I) increases [Perera and Follett, 1992;Parry et al, 1997;Dawson, 1999;Dunn and Sharp, 1999;Meddle et al, 2006;Kang et al, 2006]. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations increase in the blood, followed by gonadal development, increased sex steroid production, and reproductive behaviors [Hamner, 1968;Follett and Maung, 1978;Wingfield et al, 1993;Silverin et al, 1999;Mishra and Tewary, 1999;Dawson et al, 2001]. After several weeks of photostimulation, most birds become insensitive to photoperiod as a reproductive stimulus (i.e., absolutely photorefractory), cGnRH-I secretion and production decrease, gonads regress, and reproductive behaviors cease [Hamner, 1968;Saldanha et al, 1994;Parry et al, 1997;Dawson et al, 2001;Dawson, 2005;Meddle et al, 2006].…”