Selection for litter size, body weight, and pelt quality in mink (Mustela vison): experimental design and direct response of each trait.

In a five-generation selection experiment, separate lines of mink (Mustela vison) were subjected to selection for improved litter size at 3 wk (F line), BW in September (BS line), and underfur density (P line), and combined selection for litter size and BW (I line). Underfur density was subjectively judged on live animals. One unselected line served as a control (C line). Significant changes were achieved in each trait: litter size in the last generation was 5.3 in the F line vs 3.7 in the C line; September weight in males was 2,254 g in the BS line vs 1,979 g in the C line, and the underfur density score, graded using a 5-point scale, was 4.1 in the P line vs 2.9 in the C line. In the combined line (I line) litter size was only slightly improved, whereas BW was substantially increased (male mean = 2,194 g). A univariate animal model was used to predict genetic values and to estimate variance components with a REML procedure. Heritability estimates were .14 +/- .09 for litter size, .39 +/- .06 for September weight, and .21 +/- .06 for underfur density. It was confirmed that the reproductive performance of heavy of fat animals was poor. Responses were higher than predicted when selecting for September weight and underfur density. In the last generation the average breeding values, relative to the base generation, were +.8 kits for litter size (F line), +365 g for male September weight (BS line), and +1 point for underfur density (P line). The study suggests that negative maternal effects on litter size may exist in mink.