Seasonal variation in serum testosterone, testicular measurements and semen characteristics in the collared peccary (Tayassu tajacu).

Blood samples and testicular measurements were obtained from 4-8 captive adult collared peccaries monthly for 18 months and from wild adult males during summer (N = 16) and winter (N = 22) seasons. Serum concentrations of testosterone were determined by radioimmunoassay. Semen samples were collected monthly by electroejaculation from captive males for 1 year. Serum testosterone concentrations and testicular measurements varied in a low-amplitude circannual pattern, with maximum mean testosterone concentrations in fall and winter (1150-1400 pg/ml) and minimum values in summer (500-700 pg/ml). Circannual rhythms appeared to be related to dominance. Serum testosterone levels in wild males generally were lower than in captive males, although this difference was not significant (P greater than 0.05). Semen characteristics did not exhibit a circannual rhythm. These results suggest that the male peccary remains reproductively fertile throughout the year, yet may undergo a facultative summer quiescence influenced by ambient temperature and social factors.