Ovarian Follicle Activity in Yak versus Cattle and Buffalo

A comparison of the ovarian follicular system in cattle, buffalo and yak yields potentially useful information in developing methods for the improvement of reproduction efficiency in yaks. The ovaries in yaks were generally smaller than in both cattle and buffalo. The histological structures of the yak ovaries and follicular system resembled in all aspects those described for cattle and buffaloes. In yak, the average number of primordial follicles was markedly lower than in cattle, but higher than in buffalo. The number of growing follicles was higher than in cattle and buffalo. The number of Graafian follicles was lower than in cattle, but generally similar to that in buffalo. In conclusion, the number of follicles in each developmental phase in yaks is lower than in cattle, and higher than in buffalo. The possible roles of genetic and environmental factors in determining follicle status is discussed.