Postnatal development of the European bison spermatogenesis

The testes and epididymes of the European bison Bison bonasus (Linnaeus, 17 58) were collected from culled animals living in free-ranging populations i n Bialowieza Forest, Borecka Forest and Bieszczady Mountains, and in captiv ity (103 males, 4 months to 17 years old). We found that all bulls were sex ually mature at the age of 4 years, and some even at the age of 3 years. An imals which started mature spermatozoa production were treated as sexually mature. We observed the inhibition of spermatogenesis efficiency and involu tionary changes in epididymal epithelium after 12 years of age. Therefore, in the postnatal development of spermatogenesis three phases were distingui shed: I - development of spermatogenesis (4th month - 4th year of age), II - mature spermatogenesis (4th - 12th year), III - inhibition of spermatogen esis efficiency (over 12th year of age).