Seasonal variations in thyroxine and testosterone levels in relation to the moult in the adult male mink (<i>Mustela vison</i> Peale and Beauvois)

Abstract

Plasma thyroxine (T 4 ) and testosterone concentrations were measured in adult male mink maintained outdoors under natural light and fed ad libitum the whole year round. Plasma T 4 concentrations presented a biphasic seasonal change, the highest values occurring in the spring and autumn months and the lowest values in the winter months. The plasma testosterone cycle showed an annual maximum in January–February. The possibility of testis–thyroid interactions is discussed. The changes observed are correlated with environmental temperature, photoperiod, and molting cycle.