Photoperiodic control of fur growth and reproduction in the mink (Mustela vison)

AbstractThe influence of light on fur growth and reproduction in the mink has been investigated. Exposure of kits and adults to 4L/20D (4 light hours/20 dark hours) after completion of the summer furring cycle accelerated the development of the winter pelage. Gradually increasing the length of the daily photoperiod after growth of the winter pelage had been completed also hastened the onset of the breeding season. An abrupt change from 4L/20D to 16L/8D either inhibited gonadal development or initiated gonadal atrophy. It was also noted that mink changed from a 4L/20D schedule to a 16L/8D schedule immediately after completion of the winter furring cycle failed to begin development of the summer pelage for 10 to 12 weeks. This observation suggests that a refractory period exists in the initiation of growth of the summer pelage. However, a similar experiment conducted after completion of the summer pelage showed that the animals responded immediately to decreased light by molting into the winter pelage. It was also noted that changes leading to the development of the summer pelage occurred concomitant with or slightly after the initiation of testicular regression, while gonadal recrudescence occurred after completion of the winter furring cycle. The significance of these observations in relation to possible hypophyseal mechanisms for their control is discussed.