Early kit mortality and growth in farmed mink are affected by litter size rather than nest climate

Abstract

We investigated the effects of nest box climate on early mink kit mortality and growth. We hypothesised that litters in warm nest boxes experience less hypothermia-induced mortality and higher growth rates during the 1st week of life. This study included data from 749, 1-year-old breeding dams with access to nesting materials. Kits were weighed on days 1 and 7, dead kits were collected daily from birth until day 7 after birth, and nest climate was measured continuously from days 1 to 6. We tested the influences of the following daily temperature (T) and humidity (H) parameters on the number of live-born kit deaths and kit growth: T mean, T min, T max, T var (fluctuation) and H mean. The nest microclimate experienced by the kits was buffered against the ambient climate, with higher temperatures and reduced climate fluctuation. Most (77.0%) live-born kit deaths in the 1st week occurred on days 0 and 1. Seven of 15 climate parameters on days 1 to 3 had significant effects on live-born kit mortality. However, conflicting effects among days, marginal effects and late effects indicated that climate was not the primary cause of kit mortality. Five of 30 climate parameters had significant effects on kit growth. Few and conflicting effects indicated that the climate effect on growth was negligible. One exception was that large nest temperature fluctuations on day 1 were associated with reduced deaths of live-born kit (P<0.001) and increased kit growth (P=0.003). Litter size affected kit vitality; larger total litter size at birth was associated with greater risks of kit death (P<0.001) and reduced growth (P<0.001). The number of living kits in litters had the opposite effect, as kits in large liveborn litters had a reduced risk of death (P<0.001) and those with large mean litter size on days 1 to 7 had increased growth (P=0.026). Nest box temperature had little effect on early kit survival and growth, which could be due to dams' additional maternal behaviour. Therefore, we cannot confirm that temperature is the primary reason for kit mortality, under the conditions of plenty straw access for maternal nest building. Instead, prenatal and/or parturient litter size is the primary factor influencing early kit vitality. The results indicate that the focus should be on litter size and dam welfare around the times of gestation and birth to increase early kit survival in farmed mink.

Genetic and phenotypic parameters for litter size, survival rate, gestation length, and litter weight traits in American mink1

“…However, they reported positive significant genetic correlations between number of live born kits with survival rate at day 7 (0.42) and between number of weaned kits with survival rate at 6 mo (0.65). Schou and Malmkvist (2017) indicated that total number of living kits was significantly (P < 0.001) negatively associated with kits mortality rates (slope = −0.25), whereas the total number of born kits had a significant (P < 0.001) positive influence on kit mortality rates (slope = 0.24) in farmed mink. Furthermore, Lagerkvist et al (1994) observed that selection for litter size at week 3 resulted in a reduced genetic trend for kit mortality in mink, which was in agreement with our results.…”

“…However, this low estimate can be due to adjusting the mortality rate for number of live born kits in their study. Moreover, Schou and Malmkvist (2017) indicated that total number of kits born was positively correlated with higher risks of kit death and reduced growth rate in farmed mink (P < 0.001). In addition, studies on commercial pig breeds indicated that despite the considerable genetic improvement obtained for litter size at birth during the past decades, preweaning piglet mortality has been relatively high (Su et al, 2007;Hellbrügge et al, 2008).…”

Associations between Animal and Herd Management Factors and Urinary Tract Disease in Mink (Neovison Vison)

“…By linear regression analysis, decreased feed energy intake per female in week 17 (23 rd to 29 th of April) (p = 0.031) and increased feed energy intake per female and litter in week 24 (11 th to 17 th of June) were significantly associated with a reduction in prevalence of MUTD (p = 0.049). No associations (p > 0.05) were found between feed energy consumed and prevalence of MUTD in any of the remaining weeks investigated (w. [15][16][17][18][19][20][21][22][23][24][25][26]. Results are displayed in table 2.…”

“…Housing was according to legislation and standards for mink production in Denmark. The commercial standard-production cage system used in Denmark at the time of this study, have been previously described [16]. Each cage was additionally equipped with an elevated platform (a shelf) and a moveable soft plastic tube, according to Danish regulations for the keeping of mink.…”

Nursing of mink in nest boxes insulated with different materials

“…The survival rate of the young is determined by many factors, including color variety, age of the mother, and litter size Kołodziejczyk 2006, Kołodziejczyk andSocha 2012]. Schou and Malmkvist [2017] and Seremak et al [2013] found that litters that were too numerous had a higher mortality rate than litters that were less numerous, which was due to the fact that pups in larger litters (more than 9 young) are much smaller and the mother has limited feeding capacity. Due to the fact that mink are born naked, blind and deaf, weighing about 9-12 grams, especially during the early stages of mink rearing, maintaining an adequate nest temperature is a problem, as mink do not have a developed thermoregulatory mechanism and are prone to rapid hypothermia due to their relatively large body surface area relative to volume [Brown and Lasiewski 1972, Harri et al 1991, Castella and Malmkvist 2008.…”