Histology of ovaries treated with different doses of tannic acid. Morphological classification of follicles. (A) primordial follicle (oocyte surrounded by a single layer of flattened granulosa cells), (B) primary follicle (oocyte surrounded by a single layer of cuboidal granulosa cells), (C) secondary follicle (oocyte surrounded by two or more layers of cuboid granulosa cells without a visible antrum) and (D) tertiary follicle (follicles with a clearly defined antral space and multiple layers of granulosa cells around the oocyte). (E) atretic follicle (identified as those follicles that appear to enter the degenerative process without ovulation. In atretic follicles, the oocytes shrink or are missing, and the granulosa cells are replaced by fibrous material). (F) Proportion of ovarian atresia follicles in Brandt’s voles treated with different doses of tannic acids (n=8). Data are expressed as the mean ± sem. ***P < 0.001.