Effects of family housing on some behavioural and physiological parameters of juvenile farmed mink (Mustela vison)

Fanned mink are traditionally weaned at the age of 6-8 weeks and the kits live in male-female pairs until pelting time (approximately 6 months of age). It is possible that keeping an entire litter together with the dam in a row-cage system until pelting could provide the juvenile mink with some form of social enrichment, lasting maternal contact and a more diverse physical environment. We compared traditional pair housing of mink in standard mink cages (P group, 13 litters) with family housing in row-cage systems where several standard mink cages were connected to each other via openings in the nets separating the cages (F group, 13 litters). The F kits were housed in families of five to nine siblings and their mother. The P kits were housed in male-female pairs. Animal density was the same for both groups. There were altogether 41 F male, 33 F female, 31 P male and 31 P female kits, and 13 F and 13 P dams in the experiment. At the end of the study, the F kits had more bite scars (score 3.5 +/- 0.2 for males and 4.3 +/- 0.2 for females) than the P kits (males 1.1 +/- 0.1, females 1.3 +/- 0.1) (P < 0.05), indicating that aggression may have been more common in family-housed than pair-housed kits. The mass of adrenals (males F: 107 +/- 5 mg versus P: 123 +/- 6 mg, females F: 105 +/- 5 mg versus P: 107 +/- 5 mg, P < 0.01) and serum cortisol levels after ACTH administration (439 +/- 28 nmol/l versus 448 +/- 32 nmol/l, 457 +/- 31 nmol/l versus 501 +/- 31 nmol/l, respectively, P = 0.067) were lower in F than P kits, which might indicate that the F kits had experienced less long-term stress than the P kits. The housing system had no effect on the body mass of the kits at any time points when they were weighed, although feed consumption was lower in the F group than in the P group (209 +/- 38 g/(d animal) versus 248 +/- 15 g/(d animal)) in November (P < 0.01). In the late autumn, with sub-zero temperatures, the F animals typically huddled together in one nest box, which may have provided them with thermoregulatory benefits. These benefits might partially explain the difference in the function of the HPA-axis between the two groups. To conclude, although aggression was a severer problem in family than pair housing, the problems were altogether milder than in some earlier studies. The mink kits housed as families might have been less stressed than the pair-housed kits, but the stress results were rather ambiguous. (c) 2007 Elsevier B.V. All rights reserved.