Seasonal influences on gonadal and extragonadal sperm reserves in Small East African zebu (Bos indicus) bulls in Ethiopia.

Body weight and scrotal circumference (SC) data were taken ante mortem and genitalia collected after slaughter from Small East African zebu (SEAZ) bulls slaughtered during the wet (n = 46) and the dry (n = 53) seasons. Bulls slaughtered during the wet season were significantly heavier (47 kg) and had significantly larger SC measurements (3.3 cm) than those slaughtered during the dry season. Mean (+/- s.e.m.) paired testes weights were 233.7 +/- 13.8 and 292.8 +/- 11.3 g and epididymal weights 26.8 +/- 0.9 and 35.9 +/- 1.1 g in bulls slaughtered during the dry and wet seasons, respectively. Daily sperm production rates and epididymal sperm reserves were 2.2 +/- 0.1 x 10(9) and 3.0 +/- 0.1 x 10(9); and 16.1 +/- 0.3 x 10(9) and 17.6 +/- 0.4 x 10(9) in bulls slaughtered during the dry and wet seasons, respectively. These differences were significant. It was concluded that season affected reproductive capacity of zebu bulls probably due to variations in the quality and quantity of nutrition. However, the confounding effects of ambient temperature and nutrition on reproductive capacity of zebu bulls in tropical regions need further examinations.