Four replicate experiments were conducted to determine the effects of pinealectomy and environmental lighting on growth and thyroid function in broiler cockerels. Birds were housed in battery brooders under a 14L:10D white light regime for 2 weeks and then allotted to lightcontrolled chambers. The light environments were 14L:10D white, 14L:10D green (narrow band, 545 nm peak), and constant dark. Surgery was performed when the chicks were 3 to 5 days old. At the end of the 32-day experimental period, weight gain and thyroid weights were measured and plasma triiodothyronine (T 3 ) and thyroxine (T 4 ) levels were determined by radioimmunoassay.Pinealectomy significantly (P<.05) depressed growth but did not affect thyroid weight or circulating plasma levels of T 3 or T 4 .Birds grown under white light were significantly (P<,05) lighter in weight than those grown under green light or darkness. Plasma T 4 levels were significantly (P<.05) elevated in chicks grown under green light while T 3 levels were signficantly (P<.05) higher in dark-treated birds when compared to either light treatment.

Four replicate experiments were conducted to determine the effects of pinealectomy and environmental lighting on testes and comb weights in the broiler cockerel. Birds were housed in brooder batteries under a 14L:10D fluorescent white light regime for 2 weeks and then allotted to light-controlled chambers. Surgery was performed when the chicks were 3 to 5 days old. The fluorescent light treatments were 14L:10D green (narrow-band, 545 nm peak), 14L:10D cool white, and constant darkness. At the end of the 46-day experimental period, testes weights were determined and comb weight recorded. Pinealectomy did not affect testes weights or comb development. Darkness significantly (P less than .05) depressed testes and comb weight. This suggests that lack of light, but not pinealectomy, affects circulating hormone levels and/or tissue responsiveness in the young cockerel.