Effect of ad libitum and restrictive feeding on seasonal weight changes incaptive minks (Mustela vison)

The present study aimed to clarify to what extent different food availabili ty during one year affects seasonal weighs change and breeding body conditi on in male and female farm minks (Mustela vison). A comparison was made bet ween animals fed ad libitum and those fed a restricted food portion. The fo od intake of freely fed animals Nas higher than that of restrictively fed o nes. During March, however, the appetite of animals in each group dramatica lly declined due to breeding activities. Food intake increased after the br eeding season and levelled off during summer. Food intake increased again t owards autumn, peaking in October-November. The body weights in each dietar y group showed distinct seasonal changes. The observed-differences in food intake were also reflected in body weights. Thus, the ad libitum group typi cally had higher body weights throughout the year than the restricted diet group. The same phenomenon was seen in both sexes, although the differences in the weights of the female groups were smaller. Just before and during t he breeding season, the animals in all of the study groups had sharp weight losses. This was due to increased energy expenditure and decreased energy intake. This phenomenon obviously has an innate basis because it was found to occur despite the size of the food ration. Thus, the mink voluntarily ai ms to set its body weight to an appropriate breeding condition. A very inte nsive weight, decline in a short period should be avoided.