Ovariohysterectomy in Mares: 17 Cases (1988-2007)

Practitioners should be aware that ovariohysterectomy can be used successfully and safely in mares for various uterine diseases that are life threatening or have a high morbidity. Owners and practitioners should recognize the indications for this surgery and request it, rather than resort to ineffective medical treatment or euthanasia.

1. Introduction

Ovariohysterectomy (OHE), either partial or total, is infrequently performed in the mare for diseases such as pyometra, uterine neoplasia, extensive uterine damage and rupture, and segmental aplasia with accumulation of secretions [1-3]. Although most reported cases have survived, post-operative complications are common and life threatening and include severe uterine hemorrhage, septic peritonitis, colic, ileus, diarrhea, intermittent fever, intra-abdominal hemorrhage, uterine stump infection, jugular vein thrombosis [4], uterine stump necrosis and subsequent leakage of uterine debris [5], incisional infection, and uterine stump abscess [3]. Because most reports on OHE are individual case studies or small numbers of horses [6] from multiple institutions [3], it is difficult to draw conclusions about the surgery. In this study, we collated data from four hospitals on mares that underwent surgery with a technique previously described in a smaller number of horses and developed by the authors [6,7].

2. Materials and Methods

Medical records of mares that underwent OHE at the University of Illinois, University of Pennsylvania, University of Florida, and Klinik für Pferde, Stiftung Tierärztliche Hochschule Hannover, from 1988 to 2007, were reviewed. To maintain some consistency in reporting and in development of the surgical techniques, only horses in which the first two authors (D.E.F. and A.K.R.) did the surgery or guided it were included. Follow-up information was obtained by telephone call to owners. Seven of the 17 mares were the subjects of two previous reports [6,7].

3. Results

Thirteen mares had chronic pyometra, two mares had chronic uterine torsion, one had a chronic intramural hematoma, and one had a leiomyoma. Breeds represented were Morgan (two), Arabian (two), Quarter Horse (two), warmblood (three), Tennessee Walker, Welsh Pony, Standardbred, mixed breed horse, Berber, Appaloosa, Icelandic Horse, and American Miniature Horse. Mares with pyometra were 6 - 30 yr old, and some had histories that included assisted delivery with a difficult foaling, endometritis, and cervical scarring and adhesions. Although one mare with pyometra was severely underweight and two mares with pyometra had a history of weight loss and anorexia, the other nine were in good body condition to overweight. In these mares, different medical treatments had failed to resolve the pyometra permanently. The mare that had a chronic intramural hematoma of unknown cause had a 20-by 30-cm oval uterine mass of consistent shape and size for 2 yr, was in good health, but was infertile. The mare with a leiomyoma was 6 yr old and had a history of vaginal discharge with fluid in the uterus and a uterine mass for 5 mo.

Mares with chronic uterine torsion were Quarter Horse mares, 5 and 15 yr of age, and were presented when they were ≈280 and 313 days pregnant, respectively. One had a 2-wk history of inappetence and signs of depression, pyrexia (105°F), and tachycardia (84 beats/min). The other had a medically responsive episode of colic 4 wk before admission, was also anorexic and tachycardic (96 beats/min), and had mild pyrexia (101°F), diarrhea, and laminitis in both front feet at admission. Both mares were anemic (packed cell volume, 12.5 - 28%) and had elevated total plasma protein (8.2 - 8.4 g/dl). Peritoneal fluid was sampled from one mare and had a WBC count of 25 × 103 cells/µl (reference range, 5 - 10 × 103 cells/µl) and total protein of concentration 3.6 g/dl (reference range, <2.5 g/dl). Vaginal examinations revealed the cervix to be closed and without signs of discharge. On transrectal palpation, a large, firm, irregular mass could be palpated on the right side of the abdomen and partly obstructing the pelvic inlet, but it was difficult to determine whether it was associated with the uterus or was a separate structure. Ultrasound examination was performed per rectum and along the right flank; however, this did not help determine the nature of the mass in one mare but identified a dead fetus in the other. The broad ligaments could not be palpated.

Surgery

Total OHE was performed on 15 mares and partial OHE (right horn and ovary) was performed on the mare with intramural hematoma to improve fertility in the remaining horn. Before surgery and for 3 - 7 days afterward, all mares received potassium penicillin G (22,000 U/kg [10,000 U/lb], IV), gentamicin (6.6 mg/kg [3 mg/lb], IV), and flunixin meglumine (1.1 mg/kg [0.5 mg/lb], IV). With the exception of the two mares with chronic uterine torsion, which were processed as emergencies, preoperative protocol for others was fasting for 24 - 36 h, 1 gal of mineral oil through a nasogastric tube 12 - 24 h before surgery, and lavage and drainage of the uterus by siphon (mares with pyometra only) the day before surgery.

Figure 1. Surgery site with exteriorized uterus and ovaries, after transection of broad ligament and branches of ovarian and uterine arteries. A laparotomy sponge is packed beneath the uterine body and Best right-angled clamps are applied to retract the cervix cranially (1, direction of traction applied with clamps and uterus; 2, direction of traction applied with stay sutures; 3, direction of traction applied on first suture line). Note the numerous arteries ramifying on the uterine body at the line of transection.

With the mare anesthetized in dorsal recumbency, a 40-cm caudal ventral midline incision was made through the skin and linea alba, dividing the mammary glands if necessary. The ovarian arteries were double ligated with transfixation ligatures of size 1 polydioxanone[a] and transected on the ovarian side of the ligatures with a Serra emasculator. Dissection and arterial ligation were continued caudally in the broad ligament. If it were necessary to improve exposure to the most caudal part of the uterus, Finochietto rib spreaders, Deaver retractors, or manual retraction were used, and the hindquarters were elevated 15° above the head.

Fluid in the uterus was massaged toward the horns, and a TA-90 [b] with a previously fired cartridge, was placed caudally on the uterine body to prevent spillage and to retract it cranially. Best right angle colon clamps (7.5-cm long jaws) were more suitable for a thick-walled uterine body, with one applied from each side (Fig. 1). In one mare, a sliding loop of umbilical tape was used to encircle the uterine body and draw it cranially. In two mares, the cervix was pushed toward the abdominal incision by an assistant with a hand in the vagina. In all mares, large arteries from the caudal uterine branch of the urogenital artery ramified on the uterine body (Fig. 1), and they were individually ligated before and during transection.

Before transection, stay sutures of size 3 polyglactin 910 [c], or size 2 nylon [d] were placed on each side of the proposed line of transection in cruciate fashion as close as possible to the cervix, and simultaneous traction on them and the TA 90 or Best clamps drew the cervix toward the incision. The abdominal incision and uterus were packed off with saline-soaked laparotomy sponges. Starting on the side away from the surgeon, the first closure layer was started with size 2 or 3 polyglactin 910 or size 1 polydioxanone and tied in the uterine wall. The uterus was incised for 3 - 5 cm immediately cranial to that suture (Fig. 1). The caudal open end of the uterus was closed by continuing this suture in a Lembert pattern, and an assistant maintained traction on the suture to keep the uterine stump as close to the incision as possible. This was continued in stepwise fashion so that the uterus was incised and the open end closed in 3-to 5-cm increments, until amputation was complete (Fig. 1). The Lembert closure was oversewn with one or two Cushing layers, and the stay sutures were removed. The abdomen was lavaged with 5 - 10 l of lactated Ringers solution, and the abdominal incision was closed in continuous fashion.

For partial OHE, the surgical approach was similar to that for total OHE, and the stump of uterine horn was closed with Parker Kerr and Cushing patterns with absorbable suture material (1 polydioxanone).

OHE for Chronic Uterine Torsion

In these mares, the broad ligament was not intact, and the uterine wall was too thin and friable to allow torsion correction before foal removal. Diffuse fibrous and fibrinous adhesions from the ventral aspect of the uterus to the peritoneum, colon, omentum, and spleen were manually broken down, and a tightly constricted (<6 cm) 360° torsion of the uterus was palpated in the uterine body. Approximately 40 l of dark, bloody, mildly malodorous fluid was collected off the uterus before it was incised for delivery of a dead fetus and a completely detached placenta. The uterine incision was closed with 3 - 0 polyglactin 910 in a simple continuous pattern, the torsion was corrected, and OHE was performed.

Outcome

The most common postoperative complications of OHE were decreased appetite for 24 - 72 h after surgery, decreased borborygmi, mild colic, and decreased fecal output for 24 - 48 h after surgery. Seven mares developed mild to moderate incisional infections, and one developed a severe incisional infection. Two developed septic peritonitis that responded readily to peritoneal lavage and antibiotics. Mares were hospitalized for 2 - 17 days after surgery, and all 16 mares were recovering well at time of discharge, with normal vital signs and appetites. Sixteen of 17 mares (94%) recovered fully, gained weight and energy, and were alive at follow-up at 6 mo to 5 yr after surgery. An American Miniature Horse mare that had pyometra died within a few weeks after surgery, apparently from a septic process in the uterine stump. All survivors except the mare that had partial ovariectomy were used for riding after surgery.

4. Discussion

In this report, we describe a favorable outcome for mares treated by OHE. Care must be taken with partial or total OHE to minimize peritoneal contamination and hemorrhage, two life-threatening complications of this procedure. The cause of the only fatality was not established by necropsy and was not expected based on the mare’s progress up to hospital discharge. This was the only Miniature Horse in the series and was also the only mare with pyometra in which it was impossible to reduce the volume of purulent material from the uterus pre-operatively. Complete pre-operative drainage is not essential but does help reduce the risk of contamination. Abdominal access in this mare was also impeded by large volumes of body fat, so possibly an insufficient amount of diseased uterus was removed.

One of the greatest challenges of OHE in mares is removal of all diseased uterus. We aimed to accomplish amputation close to or through the cervix, but recognize that transection was most likely through the uterine body in most of our mares. Because of the favorable response achieved while leaving an abnormal uterine body, we question the need to remove more diseased uterus than we did. Apparently, any remaining infected uterus did not seem to cause problems, even in mares with poor drainage through a partially sealed cervix. In bitches, pyometra has been defined as a hormonally mediated diestrual disorder involving bacterial interaction with an endometrium that has undergone pathologic changes induced by an exaggerated response to progesterone [8]. Stump pyometra in bitches is associated with production of endogenous progesterone because of incomplete ovariectomy [8]. Stump abscessation has been reported in a mare that responded to treatment by cervical drainage and antibiotics [3]. Therefore, complete ovariectomy in our mares might have favored spontaneous resolution of pyometra in the remaining uterine stumps. Nonetheless, the goal of the surgery should be to remove as much abnormal uterus as possible without jeopardizing stump closure through difficult access created by a more caudal line of amputation.

Starting dissection with the ovaries and then the broad ligaments allowed most of the uterus to be exteriorized for the critical amputation procedure (Fig. 1). Steps used to minimize contamination during uterine transection were reduction of uterine contents from the body of the uterus by pre-operative drainage in mares with pyometra, application of a TA 90 instrument (Fig. 1) or angled clamps to prevent leakage from the body, use of cruciate stay sutures, packing off the abdomen, starting the first closure layer before the uterus was incised, and transection and closure in short increments. With the latter technique, some attachment of uterus to the stump was preserved during most of the initial closure, and this maintained the stump within access. A hand placed in the vagina in two mares served to identify the cervix and elevate it to the surgical field.

Results of this study showed that the prognosis for mares after OHE can be good, despite the technical difficulties of the procedure and the advanced stages of the diseases under treatment. Therefore, practitioners should not be deterred from requesting OHE in mares when it is indicated and should recognize the indications and benefits. Also, the equine practitioner should be aware of the more unusual indications for OHE in this study, such as intramural hematoma and chronic uterine torsion [7], because these were diagnostic and surgical challenges.

Footnotes

[a] PDS, Ethicon, Somerville, NJ 08876.
[b] TA Premium 90-4.8, United States Surgical Corp., Norwalk, CT 06850.
[c] Vicryl, Ethicon, Somerville, NJ 08876.
[d] Ethilon, Ethicon, Somerville, NJ 08876.