engleski

Incidence of ovulation in brown bears as indicator of range of reproductive age

In female animals the clear sign of reproductive activity is the production of ova. Additional peculiarity is some species, like bears, is conditioning the ovulation with coitus (post- coital ovulation). We searched for the earliest and latest occurrence of ovulation in two young and in two very old female brown bears. The ovaries were obtained at castration (young ones) or from dead animals (old ones), all held in captive conditions. The ovaries were histologically sectioned and stained. Both young females were in the ages of 2 years and 4 months. In the ovaries of both we found all developmental stages of follicles: primordial, primary, secondary and tertiary (Graafian) follicles. One female even developed corpus lutem what indicated recent coitus (she was kept together with a male of the same age). The old females had 36 and 31 years and both of them had infertile ovaries. Histology revealed ovarian atrophy and two subsurface epithelial cysts (SES) in case of 36 years old female and bilateral cystadenoma of SES in case of 31 years old female. These findings are frequent in geriatric female dogs and cats so it could be recognized as normally ageing changes in bears as well. The older female is known to have had litters when she was in ages of 26 and 28, and the other one was alone in the enclosure in the last 10 years of her life. Evolutionary pressure selects towards maximizing the reproductive effort. In captivity the range may even be wider than in nature. We demonstrated some of the earliest recorded ovulations as well as very late litters, but also showed that the rule "reproduce or die" doest not necessarily apply, at least in captive conditions.

brown bear; Ursus arctos; ovulation; reproductive

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