Seasonal variation in pituitary\p=n-\gonadalfunction in free-ranging impala (Aepyceros melampus)

Summary. Blood, testicular biopsies and electroejaculates were collected from adult male impala, free-ranging in the Kruger National Park (Republic of South Africa), during the breeding (rut; April\p=n-\May)and nonbreeding (September\p=n-\October)seasons. Blood samples were collected at 5-min intervals for 120 min from anaesthetized males (n = 7 impala/group) treated intravenously with saline, gonadotrophin-releasing hormone (GnRH: 1 \g=m\g/kgbody weight) or human chorionic gonadotrophin (hCG: 10 or 30 iu/kg). Semen was collected from six more animals during the breeding season and 12 animals during the nonbreeding season using a standardized electroejaculation protocol. Ejaculates obtained during the nonbreeding season were of inferior quality to those collected during the breeding season, and were characterized by lower sperm concentrations, poorer sperm motility and more morphologically abnormal sperm forms. Within season, there were no differences in testosterone secretion between the two hCG doses, and these responses were similar to those observed after GnRH, but during the rut, testosterone secretion stimulated by both GnRH and hCG was approxi-mately nine times greater than during the nonbreeding season. This seasonal increas