Influence of inbreeding on the incidence of cryptorchidism in males of Lowland-line bison

Abstract

The aim of this study was to find whether the coefficient of inbreeding is correlated with the incidence of cryptorchidism in the Bialowieza line of bison. Our study included 605 male European bison Bison bonasus (L.) born between 1971 and 2015 in the Bialowieza Forest. The animals were free-ranging as well as from captive breeding programs. Among the animals culled, there were 144 European bison calves. The calves were not considered in the research, because the descending of the testes in European bison may not occur until a year after birth. The study period, from 1966 to 2015, was divided into 5 decades. The number of male European bison born in each decade was recorded, as well as the number of cryptorchidism cases identified through necropsy in these animals. The percentage of incidence of cryptorchidism among them was calculated for every decade. Subsequently, the Pearson correlation coefficient was calculated between the number of cryptorchidism cases and the coefficient of inbreeding. In 461 male European bison older than 1 year, there were 18 cases of cryptorchidism. In the animals born in the first decade, two autopsical cases of cryptorchidism (0.045%) were recorded, and 4 cases of cryptorchidism (0.03%) were found in the animals from the second decade. Among the bison born in the third decade, there were no cases of cryptorchidism. In the fourth decade, 7 cases of cryptorchidism (0.071%) were diagnosed, and among the bison born during the fifth decade, there were 5 cases (0.111%). The Pearson correlation coefficient suggests that, as the value of the coefficient of inbreeding rises, there is an increase in cryptorchidism cases in male European bison.