Induction of winter fur growth in mink (Mustela vison) with melatonin

Adult and kit standard dark male and female mink were treated with 0, 5 or 10 mg melatonin, or a reduced photoperiod of 6 h light: 18 h dark (6L: 18D, initiated during the last week of June) to determine the effects of treatment on winter fur growth. Melatonin was administered in a Silastic implant inserted sc over the scapular region during the last week of June. Regardless of sex or age, mink treated with melatonin or a 6L: 18D photoperiod molted the summer pelage and grew the winter pelage earlier than controls (P less than .001). Winter pelage was fully prime by mid-October, 6 wk earlier than normal. Weight gain of mink, regardless of sex or age, was not affected by melatonin treatment. These findings indicate that photoperiodic effects on the growth of winter pelage in mink may be mediated through the pineal gland and its secretion of melatonin.