The effect of an improved man-animal relationship on sex ratio in litters and on growth and behaviour in cubs among farmed silver fox (Vulpes vulpes)

Earlier experiments indicate that silver foxes' fear of humans can be reduced by humans offering them feed titbits. Sex ratio, cub growth and behaviour were examined in litters produced by multiparous silver fox vixens that had been given a titbit twice a week during pregnancy (G1, N = 14) or received the same amount of human contact without any titbit(G2, N = 14). The cubs were tested in an open field (1.15 x 1.15 m square area divided into a 5 x 5 square grid) at 30 days of age, when they were in the early stages of primary socialisation. Cub activity was recorded (number of grid lines crossed [Lc] during 3 min). There was no treatment-related difference in number of cubs born or cubs weaned at 49 days (4.9 +/- 0.3 and 4.1 +/- 0.4 vs. 4.8 +/- 0.5 and 3.8 +/- 0.4 for G1 and G2, respectively; NS). However, G1 vixens delivered a significantly higher proportion of male cubs than G2 vixens (64% vs. 51%, p < 0.05; G1:3.1 +/- 0.4 male cubs, 1.8 +/- 0.3 female cubs; G2:2.5 +/- 0.4 male cubs, 2.3 +/- 0.3 female cubs). Female cubs from GI vixens were more active in the open field (G1:51.4 +/- 4.8 Lc, G2:34.2 +/- 4.7 Lc, p < 0.05) and heavier (49 days old, G1:1660 +/- 42 g, G2:1491 +/- 40 g, p < 0.01) than the female G2 cubs. No significant differences in activity or live weight were found for male cubs (activity: G1:46.4 +/- 3.4 Lc, G2:37.1 +/- 4.3 LC, NS; weight 49 days old: G1:1716 +/- 29 g, G2:1729 +/- 37 g, NS). Reduced fear of humans during pregnancy affected the sex ratio in the litter as well as the growth and activity of female cubs in the silver fox. (C) 1998 Elsevier Science B.V.