Seasonal variation in some reproductive parameters of male vicuña in the High Andes of northern Chile

Experiments were undertaken to obtain information on the effects of season on endocrine function and testicular morphology in male vicuña. Serial blood samples were taken every 15 min over 4-8 h in February and August: testes size was measured and testicular biopsies obtained. Plasma testosterone was higher (p < 0•001) in February (6•60 ± 0•35 nmol l-1) than in August (4•45 ± 0•37 nmol l-1). Longitudinal and transverse testes diameters were greater at 3•3 ± 0•22 cm (p < 0•001) and 1•89 ± 0•24 cm (p < 0•003) in February than they were, at 2•64 ± 0•18 cm and 1•50 ± 0•25 cm, in August. Seminiferous tubules had greater diameters in February (163-49 ± 29•64 μm) than in August (137•90 ± 25•15 μm); Leydig cell nuclei diameters were also greater (5•88 ± 0•97 μm vs. 4•19 ± 1•03 μm), both sets of data differing significantly (p < 0•001). February is an active spermatogenic phase and August a regression phase.