Effects of dietary caffeine on the testis of the domestic fowl, Gallus domesticus.

Roosters were fed 0-1% caffeine mixed by weight into a standard ration. With continued dietary caffeine administration, the average fertility of eggs collected for 2 weeks from untreated pullets inseminated with semen from the treated males at 0, 7 and 14 days after the start of treatment was 30-8, 33-5 and 3-3%, respectively. After 14 days of treatment fertility was significantly lower (P less than 0-001) than before (0 days) or 7 days after treatment. Semen output and sperm concentration were markedly reduced 17-21 days after treatment, and no semen could be collected from the roosters after they had received caffeine for 30 days. Removal of dietary caffeine resulted in resumption of semen production and a return of fertility to the control level. Testicular histology showed that spermatocyte divisions ceased and spermiogenesis was abnormal, although Leydig tissue and the response of the males to massage for semen collection was not affected. The effects on spermatogenesis and fertility were reversible after treatment for 30 days.