Seasonal variations in testicular morphology in Uruguayan Corriedale rams

The fine structure of the testes from young Corriedale rams raised under extensive grazing conditions in Uruguay was studied in the four seasons of a year and related to clinical, morphometric, seminal and endocrine parameters. Scrotal circumference varied significantly throughout the year, with lowest values in winter. Spermatogenic activity was present throughout the year, with minor non-significant variations in semen morphology. Structural variations could be seen in the seminiferous epithelium, particularly during winter, with the presence of affected Sertoli cells. This picture appeared similar during spring but normal morphology was restored by summer. Similar temporal changes were also detected in the Leydig cells. Plasma levels of testosterone were highest in autumn, decreased significantly by winter and were low during spring and summer. Seminiferous tubule diameter was significantly correlated with scrotal circumference and with testosterone levels. It is concluded that testicular morphology and function in Corriedale rams under extensive rearing conditions on natural pasture in Uruguay are mildly affected by the season of the year. Possible explanations are discussed.