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

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Abstract
Plasma testosterone [a measure of testicular endocrine activity] concentrations measured weekly in 16 Ouled-Djellal rams in Algeria, were lowest in autumn and early winter months, increased in Feb.-March and reached highest levels (.apprx. 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 Oct.-Nov. (50 pg/ml). The metabolic clearance rate of testosterone was low in Nov. and Jan., and significantly increased in March and June (.apprx. 2000 1/24 h). Consequently, the testosterone production rate was .apprx. 5-fold higher in June than in Jan. The short-day photoperiodic theory apparently is not applicable to all breeds of sheep or to all environmental conditions.

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