Variation of the Secondary Sex Ratio in American Mink (Neovison vison)

A statistical analysis of the secondary (at birth) sex ratio in the farming population of the American mink (Neovison vison Schr.) of the standard dark brown breed was carried out. The study was done on the materials of the Pushkin breeding farm in Moscow oblast according to the pedigree books. A total of 1550 litters of 999 mink females were analyzed. The total sample size for 5 years was 10 372 kits. On the basis of the results of the analysis in the expected population, the birth rate of males is estimated to be 0.492 +/- 0.0067 with a 95% confidence interval of 0.473 <= P(A) <= 0.511. Unlike other main species of farming fur-bearing animals, namely, arctic foxes, foxes, and sables, in the American mink, the secondary sex ratio is characterized by inconstancy and heterogeneity with a variable predominance of females or males in the offspring, depending on paratypic factors (mother's age and litter size). At the same time, as mothers age, the deviation of the sex ratio shifts toward the predominance of males in the offspring and, with an increase in the size of the litter, toward an increase in the number of females.