Superfetation in the Ranch Mink

Abstract

1. Reports of "split" litters from commercial mink ranches suggested the possibility of superfetation in this species. 2. Data have been presented in which genetically differentiated males were mated to females at intervals of 6-9 days; 14.8 per cent of the 27 litters contained offspring from both males, and 8.9 per cent of the young were sired by the first used male. 3. By the use of a system of marking corpora lutea, it was determined that mink regularly ovulate a second time in the same breeding season if a 6-7 day interval is allowed between matings. 4. The presence of blastocysts in the uterus and fertilized eggs in the oviducts of the same individual, presumably from the first and second ovulations respectively, point to a mechanism by which true superfetation may occur. 5. Superfetation is apparently a normal and regular phenomenon in the mink under the conditions stipulated, although not the rule. 6. It is suggested that superfetation as it occurs in the mink is not likely to occur in animals in which there is normally no delayed implantation.