Ovariectomy in the horse has been most commonly used for removal of abnormal ovaries such as granulosa thecal cell tumors.
Behavioral modification through ablation of estrous has become more popular and consequently more common. Recently laparoscopy
has been used to perform ovariectomies taking advantage of the minimally invasive nature of the technique. Laparoscopy alone,
is especially advantageous in cases of behavioral modification with normally sized ovaries, or ovaries up to 15 cm in diameter.
Laparoscopy can also be used as an adjunct to an open approach with laparoscopic-assisted techniques. The ovaries can be removed
with the horse standing, in lateral recumbency, or in dorsal recumbency. One of the main benefits of using laparoscopy for
the removal of abdominal structures is the direct visualization and tension-free ligation and transection that is often possible.
Photo 1: A. Standing but sedated horse in stocks with head support, B. Epidural site.
Preparation for surgery
A rectal examination should be performed prior to laparoscopic ovariectomy to identify any ovarian or uterine abnormalities
and to assess potential limitations of the procedure, specifically the size of the ovary. Transrectal ultrasonography of the
ovaries is useful to determine the presence of cystic structures within the ovary. Aspiration of cystic fluid from an enlarged
ovary may reduce the overall size of the ovary and improve the ability to ligate the ovarian pedicle and extract the amputated
ovary through a flank incision. In one mare, 1700 ml of fluid was removed from the ovary prior to ligation and transection
using a laparoscopic-assisted technique. The largest non-cystic ovary that has been removed by the author in a standing mare
was about 15 cm in diameter. The suitability of the patient's temperament for restraint in standing stocks and standing procedures
can also be determined at this time.
The mare is generally fasted for 24 hours to reduce the volume of intestinal contents and improve the working area within
the abdomen. Some surgeons prefer to feed the horses a pelleted ration for up to a week prior to surgery to reduce the bulk
of the colon. Non-steroidal anti-inflammatory drugs, such as flunixin meglumine or phenylbutazone should be administered pre-operatively,
while antibiotics can be used at the surgeon's discretion.
Photo 2: The left flank with laparoscopy portals.
For standing laparoscopy, the mare is restrained in standing stocks. The tail head and one or both flanks are clipped and
aseptically prepared depending on the need to remove one or both ovaries. The author prefers to use 40 mcg/kg of detomidine
brought to a total of 10 to 12 ml with 0.9 percent NaCl as a caudal epidural to provide systemic sedation and analgesia of
the ovarian pedicles. One or both flanks are anesthetized using either lidocaine or mepivicaine in an inverted "L" or paravertebral
pattern. Care should be taken to use only as much local anesthetic as needed. The author prefers to use no more than 50 ml
per flank. The tail is tied to keep it from entering the surgical site and the head is supported (see Photo 1). A blindfold
is recommended to limit stimulation of the sedated horse, and the ears can be plugged with gauze. The surgical field is draped
to allow access to one or both flanks as needed. The equipment cart with the video monitor is placed behind the animal. The
surgeon and the surgical assistant stand on the same side of the horse.
A 1 cm incision is made through the skin and external abdominal oblique fascia in the desired flank at the level of the ventral
margin of the tuber coxae, midway between the caudal border of the ribs and the tuber coxae. If a bilateral ovariectomy is
to be performed the author begins the surgery on the left side to take advantage of the spleen to reduce the likelihood of
visceral puncture. A mare urinary catheter is then inserted through the incision by using a steady, firm motion in a slightly
downward angle, directing towards the opposite stifle. The presence of the catheter within the abdomen is confirmed by the
sound of air entering the abdomen and the loss of negative intra-abdominal pressure. The catheter is then connected to the
insufflator and the abdomen is insufflated to a pressure of 15 mmHg with carbon dioxide.
Photo 3: Intra-abdominal photograph showing the left ovary.
Once insufflation pressure has been achieved, the laparoscopic and instrument ports are placed. The primary trochar is located
5 to 10 cm dorsal and 2 cm rostral to the insufflation catheter. A 12 mm skin incision is performed and a 10-12-mm trochar
is inserted with a slow but steady twisting motion. The trochar is removed from the sleeve, the insufflation tubing is attached,
and the laparoscope is inserted. The author prefers 15 to 20 cm long cannulas with blunt trochars for flank surgery. Pyramidal
shaped sharp trochars may lacerate blood vessels or increase the likelihood of puncturing deeper structures. The laparoscope
is attached to the light source, video camera and video monitor. An initial exploration of the abdomen is performed and the
secondary ports are then placed by replacing the insufflation catheter with one port and inserting another port 5 to 10 cm
ventral to the original insufflation incision (see Photo 2, 17).
Photo 4: Intra-abdominal photograph showing the left ovary with ovary sharply dissected from the uterus using sharp dissection.
Once the ports and instruments have been placed, the ovary is identified and grasped with the claw-toothed grasping forceps
(see Photo 3). Ten millimeter serrated scissors are used to transect the proper ligament of the ovary, located at the caudal
pole of the ovarian pedicle between the uterus and the ovary (see Photo 4). This area is minimally vascularized and also results
in transection of the mesosalpinx and uterine tube, which isolates the ovarian blood supply and provides better ligature security.
Many techniques have been used to ligate the ovarian pedicle including; suture, laser, staples, bipolar cautery, ultrasonic
devices such as the Autosonix (Kendall Animal Health/USSC), and a specialized cautery device such as the Ligasure (Valley
Lab) (See Photo 5). Using sutures to ligate the pedicle is generally the most cost effective, but requires more practice than
using the other devices. Surgical devices like the Autosonix and Ligasure incorporate cutting devices in the instruments that
reduce the need to exchange instruments frequently.
Photo 5: Methods of ligation. A. Ligation using size 1 Maxon and 4-S Modified Roeder knot, B. Autosonix ultrasonic coagulating
and cutting device, C. End of Ligasure instrument.