Changes in plasma gonadotrophins, testosterone, prolactin, thyroxine and triiodothyronine concentrations in male Japanese quail (Coturnix coturnix japonica) of a heavy body weight line during photo-induced testicular growth and regression

1. Simultaneous changes of cloacal gland area (CGA) and plasma luteinising hormone (LH), follicle stimulating hormone (FSH), testosterone (T), prolactin (PRL), thyroxine (T-4) and triiodothyronine (T-3) during photo-induced testicular growth and regression were measured in commercially bred Japanese quail from a heavy body weight line. 2. Somatically mature male Japanese quail were transferred from short days (light: dark 8L: 16D) at 10 degrees C, to long days (16L: 8D) at 20 degrees C; and sexually mature male Japanese quail were transferred from long to short days. All variables were measured at transfer and every 5 d thereafter for 35 d. 3. Transfer from short to long days caused significant increases in LH, FSH, T and testis weight (TW) after 5 d, and in CGA after 10 d. T-3 decreased after 5 d, whereas T-4 increased significantly after 25 long days and PRL did not undergo any consistent change. The testicular growth rate was k = 0.1146. 4. Transferring quail from long to short days caused significant decreases in LH and FSH after 5 d, and decreases in T, TW and CGA after 10 d. T-4 decreased after 5 d whilst T-3 increased significantly by day 15. PRL decreased significantly after 10 d then rose before declining again. The testicular regression rate was k = 0.0582. 5. The rates of photo-induced testicular development and regression in a strain of large Japanese quail did not differ from rates reported for other strains of quail. CGA was a better indicator of TW than plasma T concentrations during growth and regression. The role of PRL in photo-induced reproductive cycles in male Japanese quail remains to be determined. 6. The photoperiod-induced changes in gonad size and hormone concentrations, together provide valuable information that can be used in future studies of the endocrinology and neuroendocrinology of photoperiodism in birds.