Mating systeM and level of reproductive perforMance in Mink (NeovisoN visoN)*

the aim of the study was to examine the degree to which the mating system of female mink determines the level of reproductive performance in this species, to find out if this parameter significantly affects litter size, and if so, which of the systems used on farms is optimal. a total of 1626 mink of the foundation stock were observed. analysis was made of seven different systems differing in the number of matings and in the mating interval of the female. the effect of mating systems on the level of reproductive performance was tested by multivariate analysis of variance using least square means. the mating scheme, which in this case defined both the number of matings and the mating interval, was a factor that had a highly significant effect on litter size. regardless of the number of matings of the female, the most favourable level of reproductive performance was characteristic of the mink in which the interval between the first and last mating was the shortest. When choosing the mating system, care must be taken to ensure that it does not prolong the diapause period, which at the same time should reduce the losses associated with embryo death and resorption. key words: mink, mating system, reproduction, delayed implantation, embryonic diapause Mink reproduction has been discussed extensively in the world literature (Berglund, 1986; Elofson et al., 1989; Isakova, 2007; Lefevre et al., 2008, 2009; Møller, 1997; Rozempolska-Rucińska et al., 2004; Sulik et al., 2007; Sundqvist et al., 1989; Ślaska et al., 2009; Yamaguchi et al., 2004). This stems from the fact that mink have a peculiar reproductive physiology, mainly due to the possibility of diapause, but also from the economic dependence of the farm on reproductive performance. To ensure satisfactory reproductive performance in mink, both genetic factors and a number of environmental factors that determine prolificacy must be considered. One of the more important factors is the female mating system in its broad sense. Available research provides no conclusive answers, but clearly indicates that this factor determines reproductive performance in this animal species (Rozempolska-Rucińska This study was financed by the National Centre for Research and Development, development project no. 12-0140-10. B. Ślaska and I. Rozempolska-Rucińska 106 et al., 2004). Given the current knowledge of delayed embryo implantation and embryonic diapause in mink, it seems necessary to verify the mating system currently used on the farms. Therefore, the aim of this study was to determine the level of reproductive performance in mink according to the mating system of females and, if possible, to offer optimum solutions. Material and methods Data for the study were obtained from breeding records of a farm in the Zachodniopomorskie province. Observations were made on 1626 mink of the foundation stock, including about 58% and 42% of oneand two-year-old females, respectively. Animals represented 7 colour types (Mahogen, Palomino, Pearl Cross, Sapphire Cross, Silver, Scanblack and Scanbrown). Farmed females were mated several times: twice (36.90% of mink), three times (28.84%), four times (23.68%), and five times (10.58%). The following mating schemes were used: 1+1; 1+1+1; 1+1+1+1 (females mated on 2, 3 and 4 consecutive days); 1+1+9 (triple mating on two consecutive days, the last mating with an 8-day mating interval); 1+9+10 (triple mating with a 9and 10-day mating interval); 1+1+9+10 (quadruple mating on two consecutive days and two consecutive matings with an 8and 9-day mating interval). In addition to these mating systems, the farmed mink were also mated five times without a predetermined system. For this reason, females mated five times were included in one group in the analysis, regardless of the mating scheme. The percentage of female mink in different mating schemes was as follows: 35.81 (1+1); 2.96 (1+1+1); 0.82 (1+1+9); 25.42 (1+9+10); 0.82 (1+1+1+1); 23.35 (1+1+9+10); and 10.82% (quintuple mating). Mink were also grouped into 3 classes according to the number of days between the first and last mating: 1 to 4 days; 5 to 8 days; 9 days and above. The analyses included the number of kits born and the number of kits weaned per litter. The level of reproductive performance was analysed by multivariate analysis of variance using the least squares method, taking into account the fixed effects of female coat colour and age, mating system, number of matings, number of days between the first and last mating, and number of matings × mating system interaction. The calculations were made using SAS statistical package (SAS Institute Inc., 2000). The values of the analysed traits are shown as least square means (lsm) while providing standard errors (se) that determine the reliability of estimation. The housing and feeding conditions on the farm remained unchanged. The herd was fed in accordance with standards for carnivorous fur animals. Animals were also subjected to necessary preventive and veterinary treatments.