Early transfer of mated females into the maternity unit reduces stress and increases maternal care in farm mink

• Mink dams (n = 180) were transferred prenatal Day −36, −18 or −3 to a maternity unit.
• Mated mink dams may build and maintain a nest at least 1 month prior to delivery.
• Day −18 dams had 50% higher pre-delivery levels of faecal cortisol metabolites.
• Day −3 dams had colder nests and tended to have elevated postnatal kit mortality.
• Kits from Day −36 dams vocalized less when tested away from the nest.

Mated mammals on farms are typically transferred to another housing environment prior to delivery. We investigated whether the timing of this transfer – EARLY (Day −36), INTERMEDIATE (Day −18), or LATE (Day −3) relative to the expected day of birth (Day 0) – affects maternal stress, maternal care and the early kit vitality in farmed mink. We hypothesized that early transfer is beneficial for mink mothers and their offspring in comparison to intermediate or late movement closer to delivery, being the current practice in the commercial production. We used 180 double mated female yearlings in three equally sized groups (n = 60): (i) ‘EARLY’, transfer to maternity unit immediately after the end of the mating period, March 23; (ii) ‘INTERMEDIATE’, transfer in the middle of the period, April 10; (iii) ‘LATE’, transfer late in the pregnancy period, April 25. Data collection included weekly determination of faecal cortisol metabolites (FCM) and evaluation of maternal care: nest building, in-nest temperature, plus kit-retrieval behaviour, kit mortality and growth day 0–7 postpartum. We document that mated mink females build and maintain a nest at least 1 month prior to delivery when transferred to an environment with free access to nest building material. During the weeks before delivery, INTERMEDIATE females had 50% higher FCM concentrations than the other two groups (P = 0.002), indicative of stress. After delivery, late moved females had, in average, 2.7 °C colder nests compared to early moved females (P = 0.002). Additionally, the mortality in group LATE tended to be higher (P = 0.085) in affected litters (N = 92). Kits from early transferred females displayed less vocalization (17% vs. 40–41% in the two other groups, P = 0.015), when tested away from the nest. This indicates enhanced offspring vitality from early moved females. In conclusion, transfer into the maternity unit early after mating, rather than later during the pregnancy period, reduces stress and increases maternal care in farm mink.