Seasonal comparison of body composition and hair coat structure between mink and polecat

Water absorption and the drying and cooling rates in mink (Mustela vison) following simulated diving

The aim of the present study was to evaluate water absorbing capacity and the drying and cooling rates of fur in farmbred male mink (Mustela vison) following 10 s of simulated diving. Comparisons were made between adult animals with summer and winter fur. The water loss from a swimming pool following diving in summer amounted to 146 (s.e. 14) g and 152 (s.e. 9) g in dry and wet mink, respectively (P > 0·05). During winter the corresponding values averaged 148 (s.e. 9) and 125 (s.e. 7) g, respectively (not significant: P > 0·05). No significant differences between summer and winter were found for dry mink. In wet-coated mink, on the other hand, water loss from the swimming pool was significantly greater (P 0·05) in summer than in winter. Drying of the fur was slow and significantly (P 0·05) affected by season so that half of the 100 g water absorbed by fur evaporated within 20 min during winter (at –2°C) whereas in summer (at +18°C) it took 60 min. A slower drying rate in summer could be benefical as it allows long-term body cooling in warm environment. Cooling constants of winter-coated dry mink (0·01955 (s.e. 0·00183) per min) were not significantly different (P > 0·05) from those of winter-coated wet mink (0·02091 (s.e. 0·00144) per min) indicating that energy costs of wet fur after diving are not critical for the survivial of the mink during winter.

Body mass and composition responses to short-term low energy intake are seasonally dependent in Steller sea lions (Eumetopias jubatus)

Steller sea lions (Eumetopias jubatus) were fed restricted iso-caloric amounts of Pacific herring (Clupea pallasi) or walleye pollock (Theragra chalcogramma) for 8-9 days, four times over the course of a year to investigate effects of season and prey composition on sea lion physiology. At these levels, the sea lions lost body mass at a significantly higher rate during winter (1.6 +/- 0.14 kg day(-1)), and at a lower rate during summer (1.2 +/- 0.32 kg day(-1)). Decreases in body fat mass and standard metabolic rates during the trials were similar throughout the seasons and for both diet types. The majority of the body mass that was lost when eating pollock derived from decreases in lipid mass, while a greater proportion of the mass lost when eating herring derived from decreases in lean tissue, except in the summer when the pattern was reversed. Metabolic depression was not observed during all trials despite the constant loss of body mass. Our study supports the hypothesis that restricted energy intake may be more critical to Steller sea lions in the winter months, and that the type of prey consumed (e.g., herring or pollock) may have seasonally specific effects on body mass and composition.

Exogenous melatonin affects lipids and enzyme activities in mink (Mustela vison) liver

Exogenous melatonin as subcutaneous 2.7-mg implants was given to eight female and male minks in late July with an equal number of animals in the control groups. The liver enzyme activities and major lipids of liver and plasma were measured in October-November. Melatonin had very pronounced effects on the lipid and carbohydrate metabolism of the minks and there was also a clear sexual dimorphism. In the males, melatonin decreased the lipase esterase activity of the liver. In the liver of the females, however, melatonin increased the glucose-6-phosphatase activity. Due to melatonin treatment the liver triacylglycerol contents diminished in both sexes. At the same time, in the females the liver cholesterol levels were decreased. In the plasma lipids, the only change was a fall in the polar lipids of the melatonin-treated females. Melatonin seems to be responsible for the metabolic changes associated with the onset of wintering, especially for the acceleration of the deposition of subcutaneous fat reserves. The smaller females experience the effects of exogenous melatonin more rapidly than the males. Perhaps the smaller body size requires an earlier onset of metabolic preparation for the winter.