AUTUMNAL TIMING OF PHOTOPERIODIC MANIPULATION CRITICAL VIA MELATONIN TO WINTER PELAGE DEVELOPMENT IN MINK

摘要

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 tinder 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 tons 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 an 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 nor to be necessary for later pelage growth and maturation.