Seasonal variations in plasma testosterone and dihydrotestosterone levels and in metabolic clearance rate of testosterone in rams in Algeria.

Abstract

Plasma concentrations of testosterone, measured weekly in 16 Ouled-Djellal rams in Algeria, were lowest in autumn and early winter months, increased in February-March and reached highest levels (about 5 ng/ml) in early summer, before decreasing in autumn. Plasma dihydrotestosterone levels were very low and paralled those of testosterone until July (50 pg/ml); there was then an unexplained rise in October-November (50 pg/ml). The metabolic clearance rate of testosterone was low in November and January, and significantly increased in March and June (about 2000 1/24 h). Consequently, the production rate of testosterone was approximately 5-fold higher in June than in January. These data suggest that the short-day photoperiodic theory is not applicable to all breeds of sheep or to all environmental conditions.