Uteropexy: A new technique to improve the fertility of barren mares

After breeding, most mares effectively clear the uterus of excess semen and inflammatory products before the descent of an embryo from the oviduct five to six days after ovulation. Other mares develop a persistent post-mating endometritis that results in reduced fertility.1,2

This condition is a major clinical problem, resulting in great economic loss to the equine industry. Two equine surgeons—Palle Brink, DVM, Dipl. ECVS, Jägersro Equine ATG Clinic, Malmö, Sweden, and James Schumacher, DVM, Dipl. ACVS, College of Veterinary Medicine, University of Tennessee—have devised a surgery that may improve the fertility of mares that are barren because of this condition.

Why does post-mating endometritis occur?

The etiology of persistent post-mating endometritis is unknown, but strong evidence indicates that mares susceptible to this condition have reduced uterine clearance associated with reduced uterine contractility. The condition is especially seen in older mares. It has been suggested that since the uterus maybe be located more ventrally in the abdomen, these mares may be more predisposed to retention of intrauterine fluid after breeding compared with reproductively normal mares.3

Another study concluded that several risk factors such as age, foaling status, a history of dystocia and the stallion to which a mare is bred predispose mares to impaired uterine clearance after breeding.4 They found that about 15 percent of a normal population of Thoroughbred mares retained intrauterine fluid the day after breeding.

Clinically, mares with persistent breeding-induced endometritis accumulate fluid (semen and bacteria) within the uterine lumen after breeding.2 Delayed uterine clearance of intrauterine fluids after mating is most commonly seen in pluriparous mares more than 14 years of age.3 Increasing age and parity in the mare coincides with a lengthening of the vulva and an increase in the vulvar angle of declination, or a cranial tilting of the vulva. These changes are likely a consequence of repeated pregnancies, loss of body condition and genetics. Loss of the structural support of the caudal reproductive tract and stretching of the broad ligament from repeated pregnancies may result in the uterus tilting caudally and ventrally in the abdomen.

A study revealed that the position of the uterus within the abdomen may affect a mare's ability to rapidly clear the uterine lumen of contamination.3 It was shown that the uterus' position, determined from left and right flank scintigrams from 44 mares (24 reproductively normal; 20 that exhibited a delay in uterine clearance), had a variance in uterine conformation. The uterine-cervical angle relative to horizontal was found to be more ventral in mares with delay in uterine clearance and was more horizontal in reproductively normal mares. The researchers concluded that a uterus that tilts ventrally in relation to the pelvic brim may contribute to delay in uterine clearance and an inability of mares to rapidly clear their uterine lumen of contamination.

"In mares, the uterus gets heavy during each pregnancy, and it drops with each successive foaling," says Chris Johnson, DVM, Dipl. ACVS, Woodford Equine Hospital, Versailles, Ky. "With age and the effects of having multiple foals, the uterus, instead of being tucked up near the back bone like it should be—or at least horizontal with the ground, allowing fluid to run downhill—tips into the abdomen so it actually points down, just hanging like an old curtain," Johnson says.

These mares have poor perineal conformation. In normal perineal conformation, the anus and the vulva are in a vertical line. In problem mares, the anus starts tipping toward the head, so they have a sloped perineal conformation. This goes along with this delayed uterine clearance syndrome. "Those mares stay infected because they retain fluid in their uterus and they can't clear it out," Johnson says. "Uterine tone suffers as well."

"I don't think anybody knows why this occurs," Johnson says. "It's kind of a 'chicken-and-egg' thing. We don't know whether the uterus becomes heavy and they subsequently retain fluid and their uterine tone decreases, or whether their uterine tone decreases and they subsequently drop and retain fluid. I'm sure there are as many theories as there are veterinarians that think and write about it."

A new treatment: Uteropexy

Previously, no effective treatment had been established for these mares. Practitioners have generally tried to keep the mares as clean as they can, used uterine lavages and hormonal drugs to try to keep their uterine tone and attempted to keep them clean enough to get bred. Many of the mares, even though they have heavy, pendulous uteri, can be sufficiently cleaned up to get bred. "It takes a fair amount of veterinary intervention to get the mares in foal and to keep them in foal," says Johnson.

A new surgical intervention, uteropexy surgery, was developed by Schumacher and Brink to physically translocate the uterus from a pendulous, ventral position up to a more normal position. "I was visiting with a colleague in theriogenology about the broad ligament, and he was telling me how important he thought it was for normal uterine conformation," says Schumacher. "It came to me, that in mares with greatly lengthened broad ligaments and poor uterine conformation, we could shorten the ligament, and get better uterine conformation."

Schumacher thought these mares might benefit from elevation of the uterus to a more normal, horizontal position so that they regain normal tone and function of the uterus musculature to evacuate contents of the uterus. This procedure is a logical way to try to get these mares to clean up and get them back in foal. "Whether it will prove to be efficacious under scientific testing remains to be seen, but some of the mares we've treated have done quite well," Schumacher says.

The uteropexy procedure is a laparoscopic technique performed with the mare standing and sedated but not anesthetized. The uterus is suspended from the dorsal abdominal cavity by the broad ligament of the uterus, the mesometrium. The laparoscope is placed into the mare's flank bilaterally, starting near the body of the uterus. Suturing starts right at the bifurcation, basically plicating and, thus, shortening the broad ligament. A suture is placed where the broad ligament goes into the uterus, and then, as dorsally as possible, a bite is taken into the broad ligament. When the suture is tied together, it plicates, shortening the distance. This suturing is done in a continuous line, ending just before the oviduct enters into the uterus.

Photo 1: A mare's uterus after the broad ligament has been elevated.

About two inches of the cranial aspect of the uterus is left untouched to ensure the plumbing from the ovary to the uterus is not damaged. Essentially the uterus is sutured so it sits higher than it was before, allowing fluids to flow downhill. Once the left side is completed, the procedure is repeated on the right (Photos 1 and 2). It's just a simple continuous pattern between the dorsal aspect of the broad ligament and the ventral aspect of the broad ligament, where it inserts onto the uterus. "But it's not easy," says Johnson.

Photo 2: A mare's uterus six months after surgery.

"It took awhile to get the procedure to its current state and required the help of a colleague, Brink, expertly skilled at laparoscopic surgical procedures to help devise the technique for imbricating the broad ligament," says Schumacher. "He developed the technique using a needle holder, but because we are not as skilled at laparoscopic surgery as Brink is, we use a laparoscopic instrument that simplifies the procedure for us."

The results thus far

Uteropexy is a fairly new technique and, at this point, has been done on a limited number of mares. Brink has performed more of the procedures than any of the other investigators. For the 2008 breeding season, he shortened the broad ligament of five barren mares. Three of those mares were rebred, and all delivered foals. One of these mares was subsequently rebred and conceived. Brink operated on another four mares in 2009. Johnson has treated five mares this breeding season in Lexington. Schumacher has performed the procedure on four horses in Lexington, one horse in Tennessee and one horse in California, and he will perform one next month in Ireland. He has also performed the procedure twice with Brink in Sweden. A former colleague of Schumacher has done a few uteropexies in Australia.

"We are in the beginning stages of knowing how efficacious the uteropexy procedure is going to be," says Johnson. "It certainly does improve the perineal conformation immediately. So that's a very positive thing. I don't know if that means that we're going to buy these mares at least one more breeding season or not. To tell you the truth, that remains to be seen because a lot of the mares in my practice that the procedure was performed on have been barren for several years, and this was a last-ditch effort for these mares." Johnson says that they were generally well-bred mares with a proven record that they couldn't get in foal anymore, so there was some value.

At Woodford, they did not do exhaustive diagnostics on the mares that underwent the procedure. "That's a variable that I wish we could have avoided, but it was not going to be financially possible to do all these tests," Johnson says. "We talked about whether we might give the surgery a bad name by going this route, but that was the only route we were going to be able to try. To get this done on mares, there would be no way to test this in vitro. We were going to have to test it in vivo."

"Brink has gone back and laparoscopically evaluated three mares and noted that their uteruses were suspended in a horizontal position by a sheath of scar tissue," says Schumacher. "The sheath of scar tissue doesn't seem to interfere too much with palpation. As far as complications go, there really haven't been any. However, there has been some difficulty in performing the procedure. But as we do more and more, we're getting better and better at it."

Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. He is based in Seattle.

REFERENCES

1. Hughes JP, Loy RG. Investigations on the effect on intrauterine inoculation of Streptococcus zooepidemicus in the mare, in Proceedings. Am Assoc Eq Pract, 1969;289-292.

2. Adams GP, Kastelic JP, Bergfelt DR, et al. Effect of uterine inflammation and ultrasonically-detected uterine pathology on fertility in the mare. J Reprod Fert Suppl 1987;35:445-454.

3. LeBlanc MM, Neuwirth L, Jones L, et al. Differences in uterine position of reproductively normal mares and those with delayed uterine clearance detected by scintigraphy. Theriogenology 1998;50(1):49-54.

4. Zent WW, Troedsson MHT, Xue JL. Postbreeding uterine fluid accumulation in a normal population of Thoroughbred mares: a field study, in Proceedings. Am Assoc Eq Pract, 1998;64-65.