The Ovaries

The ovaries commonly lie in the dorsal part of the abdomen, cranioventral to the iliac wings, approximately in the plane of the fifth lumbar vertebra—the site of their initial development.

In comparison with those of other species, the ovaries of the mare are conspicuously large; indeed, in a large draft mare they may measure as much as 8 to 10 cm along the major axis. They are also remarkable for their shape because the free border is deeply indented to form an "ovulation fossa," the site of rupture of the mature follicles (Fig. 22.10). The internal structure also shows a departure from the usual arrangement. The follicles and corpora lutea are scattered within the central part of the organ and toward the ovulation fossa. They are enclosed within a dense, richly vascularized connective tissue casing that corresponds to the medulla of the ovary of other species. Because of this, even large follicles and corpora lutea do not form prominent surface elevations, and their identification on rectal exploration is more difficult than in the cow. A change in hue marks the boundary between the covering of the fossa and the common peritoneum that clothes the remainder of the organ. The position, the form, the consistency, and the general absence of marked surface projections characterize the ovaries sufficiently to allow them to be easily recognized on rectal examination.

The ovaries can be accessed for surgical procedures such as ovariectomy by making an incision through the vaginal wall about 2 inches caudal to the cervix (colpotomy) or through the abdominal wall (laparotomy) via ventral (midline, paramedian, or diagonal paramedian) or flank approaches.

FIG. 22.9 The female reproductive organs in relation to the pelvis, dorsal view. 1, Coxal tuber; 2, sacral tuber; 3, ischial tuber; 4, obturator foramen; 5, ovary; 6, uterine horn; 7, body of uterus; 8, cervix; 9, vagina; 10, vulva.