An anatomical study of the internal genital organs of the yak at different ages.

Forty-five female yaks of different ages with known reproductive histories were used to determine the anatomical characteristics of their internal genital organs. The results showed that there were several follicles of different sizes present on the surface of each examined ovary, up to a maximum of 13. In each age group, a greater number of follicles < 5 mm was observed in the right than in the left ovary (P < 0.05), while the number of follicles > 5 mm in the right ovary was almost the same as that in the left one. The average sizes and/or weights of the ovary, oviduct and uterus became larger or heavier with increasing age, and significant differences occurred between age groups (P < 0.05). The shapes, locations and other anatomical characteristics of the different internal genital organs are also described.