The potential advantages and disadvantages of ovariectomy over ovariohysterectomy have recently been discussed.1 Proponents of ovariectomy assert that the procedure is a more efficient and less invasive method to sterilize female dogs and cats. However, in North America veterinarians have predominantly been trained to perform ovariohysterectomy. Since ovariectomy is unfamiliar, veterinarians may have concerns about the technique and whether uterine disease could occur as a consequence. With this article, I hope to describe the procedure in a way that allows you to perform it with confidence and to understand its effects.
In carnivores, the ovary is located within the ovarian bursa, which is a peritoneal recess created by the mesosalpinx, mesovarium, and ovary itself. Some may refer to the mesosalpinx as the ovarian bursa. The ovary is attached dorsocranially to the suspensory ligament, which originates from the last rib.3 The short proper ligament of the ovary passes between the ovary and the tip of the uterine horn. The round ligament passes from the cranial end of the uterine horn within a fold of peritoneum laterally from the broad ligament toward the deep inguinal ring. Within the bursa, the ovary is attached along its length to a band of dense connective tissue joining the proper and suspensory ligaments. The opening to the bursa is a small slitlike orifice on the medial aspect.
In bitches, the ovary is often almost completely enclosed.4 A mature bitch often has large fat deposits in the mesosalpinx and mesovarium, obscuring the location of the ovary and its blood supply. However, the ovary may be observed through a thin, round area of mesosalpinx on the lateral surface of the bursa.4 In queens, the mesosalpinx is much smaller, contains little fat, and partially covers the lateral surface of the ovary.
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The uterine tube (also known as fallopian tube, oviduct, and salpinx) passes within the mesosalpinx from its origin adjacent to the ovary to join the tip of the uterine horn.4 The ovarian artery and vein have tortuous branchings within the mesovarium and supply the ovary, the uterine tube, the mesosalpinx, and a part of the suspensory ligament. The ovarian artery and vein each contribute a branch to the cranial portion of the uterine horn.5 The uterine artery parallels the uterine horn and terminates supplying the uterine tube. The ovarian and uterine veins roughly parallel the arteries but may anastomose.5
INDICATIONS AND EFFECTS
Removing both ovaries eliminates the manufacture of hormones (estrogen, progesterone, inhibin, activin, and follistatin) and female gametes by the ovaries.6 This results in reproductive sterility and the elimination of estrous cycles, which prevents heritable diseases and reduces interference with the management of diabetes, epilepsy, and demodecosis.7 It prevents ovarian neoplasia, vaginal hyperplasia, vaginal prolapse, cystic endometrial hyperplasia, and pyometra and reduces the risk of mammary cancer in dogs if performed before 2 ½ years of age.7,8 Flank-based ovariectomy may be a practical treatment for feline mammary hyperplasia.9 And ovariectomy may improve the survival of dogs being treated for mammary cancer.10,11
Although bilateral ovariectomy eliminates naturally occurring cystic endometrial hyperplasia and pyometra, the possibility of uterine neoplasia remains. This risk appears to be low even in intact bitches, and the uterine tumors reported have mostly been benign.1
Unilateral ovariectomy is indicated for unilateral ovarian neoplasia or disease (cysts, infections) when maintenance of fertility is desired.