The early transfer of mink kits from large litters to a foster mother with fewer kits is relatively unstudied, although relevant in practice. Therefore, over two birth seasons (2018-19), we studied four factors: (1) the timing of transfer, i.e. cross-fostering D2 or D6 after birth, (2) the dam experience, i.e. first vs. older
(second/third year) recipient dams, (3) prolonged early lactation period with 0, 2 or 4 days, by transferring kit to a later born litter and (4) the recipient litter size, i.e. small: 1-3 vs. medium: 4-7 kits. The 2018 study (factor 1 and 2) included 406 kits from large (9-14 kits) litters transferred to 406 foster mother (4-7 kits) litters either D2 or D6 after birth. The 2019 study (factor 3 and 4) included 572 litters (186 sender and 386 recipient litters receiving one kit). The data collection was from birth (D0) to weaning (D56): maternal retrieval of unfamiliar kit at transfer, kit mortality, growth (weight D1, Day of transfer, D28 and D56) and kit damages/wounds 7 weeks after birth. The 2018 study demonstrated that mink dams retrieve the unfamiliar kit quicker into the nest box D2 than D6 (Survival Analysis, SA; P<0.001). Further, the kit weight at weaning (ANOVA) was higher
following D2 than D6 transfer to equally aged litters (in avg. +24 g, P=0.032). The 2019 study demonstrated the possibility of successfully prolonging the early lactation period experienced by the foster kit (not the dam), i.e. 4 > 2 > 0 days, for increased growth in foster kits (P<0.001). The newly delivering mink mothers had the quickest accept of an older kit from a large litter, i.e. D2 was better than D4 for the recipients (SA P=0.019). Small recipient litters (1-3 kits) resulted in a reduced occurrence of damages to the kits, particularly true for the vulnerable female kits around week 7 after birth. For both years of study, the growth of kits until weaning was markedly higher in the litters nursed by the older, experienced foster dams (P<0.001). Thus, farmers are recommended to use experienced rather than inexperienced foster mothers during early cross-fostering in mink.
