A. SOLAK, Ts. TAKEVA and Ts. TSVETKOV
Institute of Cryobiology and Food Technologies, BG-1407 Sofia, Bulgaria
SOLAK, A., Ts. TAKEVA and Ts. TSVETKOV, 2005. On structure of atretic follicles in the ovary of hibernating mammals. Bulg. J. Agric. Sci., 11: 531-537
Studied were the ovarian atretic follicles of 64 ground squirrels, distributed in four seasons. Female ground squirrels have an expressed seasonal periodicity of the sexual cycle. Their reproductive cycle starts in the second half of March. The estrus continues for 10 days, and the pregnancy lasts 26-28 days. The hibernation starts from the middle of September and continues till mid March. Atretic follicles can be steroidogenic and non-steroidogenic. Steroidogenic follicles are mainly of the thecal type and nonsteroidogenic are fibrous bodies. Frequent are follicles with two oocytes. One of them, as well as the surrounding granulosa cells, are affected by dystrophic changes. The rest of the follicle continues to develop and may reach ovulation. This phenomenon is seen in hibernating mammals, mainly in ground squirrels. The atresia is very expressed in March, April and May.