Effects of castration and testosterone treatment on the development and involution of the bursa of fabricius and the thymus in the Japanese quail.

We investigated the effects of castration on the development of lymphoid organs (bursa of Fabricius, thymus, and spleen) in the Japanese quail during 4-8 weeks of age under a long photoperiod (16L:8D) and the effect of testosterone implantation on the involution of the lymphoid organs under long (16L:8D) and short (8L:16D) photoperiods. Under 16L:8D, the bursa of Fabricius and thymus in intact quail grew rapidly and reached a peak at 6 weeks of age and regressed thereafter. In contrast, development of the lymphoid organs in castrated quail was well correlated with the body growth. Testosterone treatment induced a significant reduction in relative bursal weight to body weight at 6 weeks of age under 16L:8D and 8 weeks of age under 16L:8D and 8L:16D, in relative thymus weight at 6 weeks of age under 16L:8D and 8L:16D, and in relative spleen weight at 6 weeks of age under 8L:16D. Thus, we conclude that gonadal hormones play an important role in the development and involution of lymphoid organs.