Histological observations on spermatogenesis and folliculogenesis in gonads of Japanese black bears (Ursus thibetanus japonicus) captured in Niigata prefecture [Japan]
1999
Niimura, S. (Niigata Univ. (Japan). Faculty of Agriculture) | Ohtaki, K. | Eguchi, T. | Kusuhara, S. | Miura, S. | Abe, M.
Spermatogenesis in testes and folliculogenesis in ovaries were histologically observed in 25 male Japanese Black bears (2 to 11 years old) and 13 female ones (1 to 15 years old), captured in Niigata Prefecture from April 1996 to April 1998, to evaluate the age of reaching sexual maturation. The percentage of male hears having spermatogenic cells that developed more maturely than spermatocytes in the seminiferous tubules was 60% (3/5) at the age of 3 and 100% (l9/19) at the ages of 4 to 11. However, one 2-year-old male had spermatocytes in the seminiferous tubules although there was only one such hear. On the other hand, a great number of large antral follicles were observed in ovaries of none of females at the age of one, but all of females at the ages of 3 to 15. From these results, it was suggested that male and female bears living in Niigata Prefecture reach sexual maturation at the ages of 4 and 3, respectively
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