Prolonged nest building increase the reproductive outcome in American female mink

ABSTRACT: The timing of the onset of maternal-related nest building in American Mink is unknown,  and it is expected that farmed mink are highly motivated to perform nest building during times of restricted access to nesting material on mink farms.  Not fulfilled motivations due to thwarting can lead to stress response with increased HPA­-axis output and performance of abnormal behaviour. We aimed to investigate when maternal nest building have onset and to test how prolonged access to nesting material influences dams stress response and reproductive outcome. We set up two groups that differed in timing of allocation of nesting material in the cage: group ALWAYS from 15 January and group REGULAR from 23 March. On 16 January after allocation of nesting material to ALWAYS, the mink built advanced nests, and their nest scores (P < 0.001) and nest temperature (P < 0.001) stayed significantly higher through to 23 March. When both groups had access to nesting material, from 23 March through birth, no difference was found in nest score (P = 0.28) and temperature (P = 0.27). ALWAYS mink females had better reproduction outcome: offspring survival (P = 0.007) and litter size (an average +1.2 young) Day 7 after birth (P = 0.021). Additionally, access to nesting material during winter/early spring (group ALWAYS) tended to reduce females’ faecal cortisol metabolite concentrations (FCM; P = 0.075) and the performance of active behaviour including stereotypic behaviour (P = 0.008). After mating, maternal nest building was documented as the nest scores increased through the period 24 March to Day 2 after birth. During this period, when both groups had equal access to nesting material, no differences was found in FCM, stereotypic and active behaviour, nest score and nest climate. In conclusion, the current study demonstrated for the first time that adult mink females are motivated for nest building prior to  mating, during winter/early spring, thus it is not only a maternal behaviour. Further, prolonged access to nesting material in the cage had a stress-­reducing effect and a positive long-term effect on the reproductive outcome in farmed mink.