Influence of nest box environment on kit survival

Abstract

Hypothermia is considered as one of the major risk factors increasing mortality in the kits born. However, very little is known about the preferred nesting materials for nest building and the link between nest building and kit survival in mink. To investigate these questions, we used 105 farmed mink females divided into 4 groups, non-pregnant females (NON), pregnant females with access to one resource of nest building material (RES-1), pregnant females with access to three resources (RES-3), and pregnant females with access to one resource but which were moved into a climate-controlled facility (CLIMA). CLIMA was video recoded in order to describe the time course of nest building prior to parturition. The quality of the nest was scored once a week for five weeks prior to delivery using nest scores of 1–5 (1: no nest, 5: full nest with cover). Kits were counted on day 1 and on day 7 after delivery. We discriminated between stillborn and live-born kits dying early using autopsy. The access to more than one resource (RES-3) of nest building material had a profound effect on kit mortality in the first week of life compared to access to straw only (χ2(1) = 13.7, P<0.001). In RES-1 ~20% of the kits died from day 1–7, and only ~5% in RES-3. The risk of dying was approx. 4 times higher for a kit live-born into the one resource environment. RES-3 females were building better nests and stayed in the nest box longer around parturition than RES-1, which could explain the higher mortality in this group. In conclusion, access to different nesting materials reduced the risk of dying in farm mink in relation with factors as e.g. nest quality and maternal behaviour. A decrease in kit mortality from 20% to 5% would give the Danish mink production a profound number of Danish kroner extra per year.