Determination of reproductive span through morpho-histological studies on the ovaries of captive brown bears (Ursus arctos)-a short communication

Abstract

The study aimed to determine reproductive span by investigation of the ovarian structures in young and elderly captive brown bear females (Ursus arctos). The ovaries of two 2-year-old females were obtained by ovariectomy and during the necropsies of 31 and 36 year old individuals. All the obtained ovaries were examined macroscopically and histologically. Histological examination of the ovaries of young animals (2+ years) revealed the presence of primordial, primary, secondary and tertiary follicles within the ovarian cortex. One ovary showed a mature corpus luteum, indicating recent ovulation, what is, to our knowledge, the first histological proof of the earliest age of ovulation recorded for captive brown bears. Ovarian atrophy accompanied by the development of multiple cystic subsurface epithelial structures (SES) in the case of the old bears in this study indicates that the ovaries of brown bears share similar degenerative and proliferative patterns with domestic canids. The oldest female had records of successful births at the ages of 26 and 28 years. Both recorded birth events represent one of the latest confirmed occurrences of ovulation, conception and birth amongst brown bears.