Induction of precocious development of reproductive function in cockerels by tamoxifen administration.

To examine the effects of tamoxifen, a known estrogen antagonist in the chicken, two groups of cockerels were injected every other day from hatching until 7 weeks of age with 1 and 10 mg tamoxifen/kg body weight (BW), respectively. A third group was injected with 1 mg tamoxifen/kg BW every 3 days from 5 to 10 weeks of age. All groups treated with tamoxifen had increased testes weight, but BW and pituitary weights did not differ from controls. In contrast to controls, seminiferous epithelium of testes from treated cockerels showed spermatogenesis up to the spermatid elongation stage. We suggest that the antiestrogen effect of tamoxifen increased circulating LH, which stimulated testes growth and precocious spermatogenesis.