Postnatal development of the European bison spermatogenesis

The testes and epididymes of the European bison Bison bonasus (Linnaeus, 1758) were collected from culled animals living in free-ranging populations in Bialowieza Forest, Borecka Forest and Bieszczady Mountains, and in captivity (103 males, 4 months to 17 years old). We found that all bulls were sexually mature at the age of 4 years, and some even at the age of 3 years. Animals which started mature spermatozoa production were treated as sexually mature. We observed the inhibition of spermatogenesis efficiency and involutionary changes in epididymal epithelium after 12 years of age. Therefore, in the postnatal development of spermatogenesis three phases were distinguished: I - development of spermatogenesis (4th month - 4th year of age), II - mature spermatogenesis (4th - 12th year), III - inhibition of spermatogenesis efficiency (over 12th year of age).