Quantitive collection of night-time urine every 2nd week was used to elucidate the temporal relationship between changes in melatonin production, weight gain, and priming of the winter pelage under natural light conditions and under a long photoperiod (18L: 6D) imposed at different times in four groups of female mink during autumn. In mink maintained outdoors under the natural photoperiod (group 1), melatonin excretion was 1·80 (s.d. 0·80) ng per night (no. = 3) at the beginning of September, thereafter it began to decrease slowly until November when it was only 0·62 (s.d. 0·32) ng per night. These mink had a normal autumn moult during the first half of October and the winter pelage was mature at the end of November. When mink maintained outdoors were transferred to 18L: 6D on 7 September (group 2), excretion of melatonin decreased promptly, autumn moult was disrupted and winter fur priming delayed. Long photoperiod after mid October (group 3), did not interfere with pelage maturation despite the decrease in melatonin production. Mink implanted with melatonin on 14 July (group 4) showed very high melatonin excretion in early September. In these animals the winter pelage growth was unaffected by the long-day conditions; the pelage matured in mid October. Body weight increased in mink of all groups during autumn. This increase levelled off or a weight loss (group 2) was seen along with the final hair maturation. Activation of hair follicles occurred during a 4 to 6 week period. According to these results, melatonin is the photoperiodic signal to autumnal weight increase and autumn moult but seems not to be necessary for later pelage growth and maturation.

An experiment was conducted to evaluate the effect of dietary cimaterol, a β-adrenergic agonist, on growth, carcass characteristics and pelt quality of kit mink. The 40 standard dark and 40 sapphire mink kits were assigned to a control or to one of three treatment groups (five males and five females of each colour phase per group). Treatment consisted of the inclusion of 0·5, 2 and 5 mg cimaterol per kg (dry) of a standard ranch mink diet (control). All animals were weighed at the initiation of the experiment (24 July) and at 28-day intervals until 16 October. At slaughter (12 December) body weights were recorded and pelts measured for length and evaluated for fur colour and quality by experienced fur graders. Samples of fur from similar sites on each animal were removed for measurement of guard hair and underfur diameter. Frozen carcasses were analysed for protein and fat content. Mink final weight decreased with increasing concentrations of dietary cimaterol (P < 0·05). Pelt length, which was found to be highly correlated with body size, was also reduced by cimaterol treatment. Feeding 2 and 5 mg cimaterol per kg diet to male kits, and 5 mg/kg to female kits caused a significant reduction in the proportion of carcass fat and increased the proportion of carcass protein (P < 0·05). Fur fibre diameter for both guard hair and underfur was not significantly affected by dietary cimaterol. There was also no significant effect of cimaterol treatment on fur quality. Cimaterol treatment did not result in diversion of nutrients from body proteins to the synthesis of fur and pelt proteins. Results of this research indicate that oral administration of cimaterol to mink will be of little practical value in fur production.