Is spermiogenesis common or rare in young male European bison aged 2 and 3 years?

The aim of the present study was to determine how often spermiogenesis occurs in young male European bison up to 3 years old. Research was performed on sections of the testes and epididymes collected from 51 male bison aged 2-3 years. The animals were divided into 2 age groups: young males up to 2 years and young males up to 3 years old, with further separation into specimens with or without spermiogenesis. The animals were culled during the autumn-winter seasons in 1994-2008 (after rutting period) in the Bialowieza Primeval Forest. Spermiogenesis in the 2-year-old animals was a rare condition found in 16.7% of cases. However, at the age of 3 years more than half of the individuals examined (53.3%) had spermiogenesis. Young males up to 2 years old with spermiogenesis were characterized by a significantly higher body weight and their right testis also weighed more than the left testis of the animals without spermiogenesis, the difference being on the border of statistical significance. There was no significant differences in the body mass and weight of the left testis between older animals, up to 3 years old, with or without spermiogenesis. However, young males up to 3 years old with spermiogenesis were characterized by a significantly higher weight of the right testis than those without spermiogenesis.