Summary. 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 paralleled 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.