Concentrations of androstenedione, testosterone and LH in the blood before and after the onset of spermatogenesis in the cockerel

Spermatogenesis begins at about 16 weeks of age in Thornber 909 cockerels when subjected to a lighting schedule of 14 h light/day. Most birds produce semen by 24 weeks. The onset of spermatogenesis is associated with increases in the concentrations of plasma LH and testosterone (Sharp, 1975; Sharp, Culbert & Wells, 1977). In the present study these increases are related to changes in the concentration of circulating androst-4-ene-3,17-dione (androstenedione). This steroid is one of the androgens secreted by the mammalian testis (Eik-Nes & Hall, 1965) but little is known about its secretion in birds. Additionally, concentrations of LH, testosterone and androstenedione were measured for 4 months after the birds began to produce semen.