The Effect of Early Weaning on the Sexual Behavior and Reproductive Success of Ranch Mink

Abstract

The effects of early weaning on the sexual behavior and reproduc- tive success of ranch mink (Mustela vison) were tested. Male and female mink were weaned at various ages from 5 to more than 10 weeks after birth. The be- havior associated with reproduction during their first breeding season was analyzed and a critical socialization period for exhibition of this behavior delimited. Females weaned prior to 8 weeks post-partum were significantly easier to breed than females weaned at 8 weeks of age or older. Successful breeding performances by the males apparently depended on a critical period of socialization in the litter en- vironment occurring within 5 to 8 weeks after birth. Visual isolation appeared to inhibit reproductive behavior somewhat, possibly due to an asynchrony in physio- logical development. The experience achieved in ludic behavior during the early period of so- cialization of a mammal is considered as a necessary prerequisite for normal expression of adult behavior. Scott (1962) attributed learning in play ac- tivities to be defined in critical periods of socialization. However, conflicting evidence regarding the effect of raising male mammals in isolation on sexual response was reported by Beach (1958) and Folman and Drori (1965). These differences in results may be explained by comparison of the ages at which the animals were weaned. If the social contact was eliminated before the critical socialization period for adult sexual behavior, abnormal responses might be expected regardless of social environment thereafter, Certain difficulties have been encountered with the use of young male ranch mink (Mustela vison) during their first breeding season. The number of females impregnated and therefore litters produced by these males are lower than when more mature males are used (Enders, 1952). In this study we attempted to correlate socialization of the male and visual isolation with breeding performance and to delimit the critical socialization period for ex- pression of this behavior. The breeding performance of female mink weaned at different ages was also studied to determine if differences attributable to weaning age existed.