A small percentage of broodmares will be afflicted with urine pooling, also known as vesicovaginal reflux (VVR) or urovagina. But when it does occur, it is a serious problem that sometimes can only be remedied with surgery. Simply put, urine pooling occurs when urine refluxes forward in the vagina and against the cervix instead of being flushed to the rear and evacuated through the vulva. The problem is at its most severe when the mare is in estrus because then the cervix is relaxed and the urine may enter the uterus, irritating and contaminating it.
Urine in the cranial (forward) portion of the reproductive tract as well as in the uterus itself produces chemical irritation, plus spermicidal activity. The irritation it causes can provide a breeding ground for harmful bacteria.
Older mares which have delivered a number of foals are more at risk than their younger counterparts, says Gayle Trotter, DVM, a surgeon at Colorado State University who has written textbook literature on the problem and the surgical procedures involved in correcting it.
When the problem occurs in younger mares, says K. Jack Easley, DVM, MS, of Shelbyville, Ky., and also the author of textbook literature on VVR, it could mean urine pooling with added complications. The young mare might have an ectopic ureter--displacement of the tube that conveys urine from the kidney to the bladder--and, as a result, might empty urine into any area along the reproductive tract. This is a problem that can only be solved with surgery.
Nature has equipped the mare well to prevent uterine contamination and urine pooling, providing her conformation is correct and she doesn't develop problems as the result of multiple births.
The posterior or caudal end of the reproductive tract is the vulva. The tract extends forward through the vestibule and opens into the vagina. The urinary bladder lies just beneath the forward part of the vagina and the cervix. Ventral (below) to the cervix lies the vaginal fornix, which is the deepest and most cranial (forward) portion of the vaginal vault.
There are basically three lines of defense to prevent contamination of the uterus. The first is the vulva, which is designed to close tightly and protect the reproductive tract from contamination by air or debris. If the vulvar labia become weakened and do not function properly by providing a tight outer seal, air can be drawn into the reproductive tract, inflating the vaginal vault (wind sucking). The intake of air may compromise the tract's second line of defense.
The second line of defense is the vulvovaginal fold or vestibular sphincter, located just forward of the urethral orifice.
"The vulvovaginal fold," Easley writes, "consists of a transverse fold or remnant of the hymen and the pelvic floor ventrally, the caudal constrictor muscles laterally, and the perineal body dorsally."
Its job is to seal off the forward portion of the reproductive tract and prevent urine from flushing toward the cervix. Urine pooling can occur when the vulvovaginal fold does not function properly. One cause is a relaxed state of the vaginal vault due to an influx of air. Another might be an alteration of its location in relation to the urethral orifice because of conformational problems. Still another is the loss of muscle tone along the reproductive tract due to multiple births or injury.
The final bastion of defense for the uterus is the cervix itself. When the mare is not in season, it normally does its job well, tightly sealing off the uterus against all contamination. However, during estrus the cervix relaxes and is a poor defender against contaminants. If a mare is a urine pooler, it is during estrus that urine will flush directly into the uterus, compromising both uterine health and conception.
"Ideally," Easley writes, "urine is evacuated from the bladder into the vulvar vestibule and out the open vulvar labia, or lips. However, if the normal slope of the vulva is altered approximately 10 degrees from horizontal or the genitourinary tract slopes cranioventrad (forward and downward), a splashback of urine can occur, whereby some urine refluxes back toward the cervix and uterus instead of out of the vulva. This condition can lead to an accumulation of a variable amount of urine in the vaginal fornix (urine pooling).
"Uterine secretions or urine accumulation in the vaginal fornix lead to and/or intensify vaginitis and cervicitis. During estrus, when the cervix relaxes and opens, urine may flow back into the uterus and cause endometritis. Chronic irritation from urine changes the pH of the vagina and affects sperm viability, which, in turn, compromises the mare's chances of becoming pregnant.
"Reduced conception rate is only one danger associated with vesicovaginal reflux. Allowed to persist, endometritis can lead to periglandular fibrosis, as well as premature regression of the corpus luteum, causing a deficiency of progesterone and early embryonic loss.
"Infertility in the mare associated with VVR must be managed as a complex problem. Complete reproductive evaluation of the mare is necessary to establish the cause of VVR and for proper treatment."
A mare's conformation, particularly a high tailset, might predispose her to urine pooling. Mares which are wind suckers (pneumovagina) are prime candidates to develop VVR. When the mare suffering from pneumovagina draws air into the reproductive tract, the vaginal vault is inflated and the entire reproductive tract becomes relaxed, providing an opportunity for urine to enter through the open second barrier, the vestibular sphincter.
Another reason that sphincter probably doesn't work well anymore in some mares, says Trotter, is because of the bad conformation that has developed (often from multiple birth). The loss of muscle tone allows the vagina to tilt forward and the sphincter is unable to provide a tight seal in the tract.
"The most common scenario (for urine pooling) is found in multiparous (multiple births) mares with poor reproductive tract tone or damage to the vulval suspensory ligament, anal retractor muscle, and vulvar constrictor muscles," Easley reports.
"The pelvic viscera, vulva, and vagina are displaced in such a way that the reproductive tract then descends craniad (forward) and ventrad (downward). The urethral orifice is then cranially displaced over the crest of the ischium, or pelvic floor, and a variable amount of urine flows into the vaginal fornix."
There is a bright spot in these rather discouraging scenarios, says Trotter. During estrus, a mare's disease-fighting capabilities are at their zenith.
"During estrus, most of the defense mechanisms are working maximally against infection," Trotter explains. "That's the positive side of the tradeoff. Everything in the mare's system is geared up to combat infection at that time."
There is still another side to the coin. Some mares will urine pool only when in estrus. This is listed as the least serious of urine pooling problems and also the one most easily treated as surgery might not be necessary.
Easley explains it like this: "Depending on stage of estrus and concentrations of estrogen and progesterone, the reproductive tract may be predisposed to urine pooling. Estrogens stimulate and maintain the tissues of the tubular reproductive tract by increasing vascularity and uterine secretions, therefore increasing the area's defense against mechanical insult and infection. A side effect, however, is a mild edema of the tubular tract, vagina, and uterus, resulting from intracellular absorption of water. The pelvic structures and vulva then relax as the general perineal area enlarges and cranial displacement of the reproductive tract follows, leading to vesicovaginal reflux (urine pooling)."
Often, says Trotter, a mare like this can be managed successfully by manually evacuating the urine, then breeding her. If a pregnancy occurs, the mare's hormonal changes will cause the reproductive tract to return to its normal, firmed-up state and the cervix to tightly seal off the uterus.
Because the urine pooling problem might only be a mild one that can be solved without surgery, it is very important that the correct diagnosis be made. A surgical procedure on a mare which pools urine only during estrus might do more harm than good.
Trotter, however, adds a note of caution involving mares which only pool urine during estrus: "Some of these mares become pregnant if the urine is manually evacuated prior to breeding. However, some of these mares also likely suffer early embryonic death of the fetus or accumulate urine more significantly in subsequent years. A full reproductive workup, including a uterine biopsy for prognostic purposes, is recommended prior to embarking on a course of medical or surgical treatment."
Although some cases of urine pooling are easily treated, there remains the bad news side of the issue--mares which have serious urine pooling problems that require surgery.
For the wind sucking (pneumovagina) mare which also is a urine pooler, a simple Caslick operation that closes off the upper portion of the vulva, allowing only an opening for urine to be evacuated, might be sufficient.
However, even with this relatively common surgery, care must be taken not to overdo it.
"Another predisposing factor in VVR," Easley reports, "is an excessive Caslick operation or episioplasty that has extended too far ventrad (downward) and prevents passage of the proper outflow of urine from the vulvar area."
When a correct Caslick procedure does not solve the problem, more involved surgery might be required.
"If both the vulvar and vestibular seals are ineffective," Trotter reports, "the Caslick procedure will not correct the problem. This is the situation seen commonly in older, multiparous mares with a sunken anus and vagina, or in some mares that have had extensive second-degree rectovestibular injuries."
Often the surgery of choice in those cases, says Trotter, is urethral extension or urethroplasty. Simply put, the surgery involves constructing a tunnel with existing tissue that is three to three and one-half inches long from the point where urine from the bladder is normally evacuated through the urethral orifice and running rearward to the vulva. When it works as it should, the tunnel carries the urine rearward and evacuates it through the vulva instead of allowing it to reflux toward the cervix.
Various practitioners, says Trotter, have modified the basic procedure, utilizing individual approaches that have proven successful for them.
The greatest hazard to overcome, Trotter says, is the development of fistulas or tiny holes along the tunnel. When that occurs, he said, urine leaks through and the problem of urine pooling might remain unsolved.
What is the procedure's success ratio?
That is a difficult question to answer, Trotter says, because there is not a lot of literature on the subject.
However, in one report on a form of urethral extension surgery, it was recorded that pooling of urine was eliminated in 16 of 18 mares. Fistula formation and continued pooling were observed in the remaining two mares. Of 11 mares known to have been bred after surgery, seven were known to have conceived.
Utilization of a similar technique that required less tissue dissection, Trotter reports, was successful after a single surgery in 12 of 15 mares.
A technique credited to A. O. McKinnon, DVM, and J. O. Beldon, DVM, that resulted in a much larger and stronger tunnel to allow for complete and easy evacuation of urine, produced a success rate that was even higher.
In one report where this procedure was utilized successfully, correction of urine pooling was reported in 32 of 34 mares. Fistula formation occurred in five of the 34 mares. When this procedure is utilized, Trotter says, mares normally can be bred about one month following surgery.
The urethral extension surgery normally is done with the mare sedated, but standing. The procedure takes him approximately one hour, Trotter says.
In mares with exaggerated conformational problems an additional surgery--perineal body transection--might be called for. "If the anus is really recessed," Trotter says, "the surgery transects the muscle attachments between the GI tract and the reproductive tract. You remove the forward pull that the rectum and GI tract are making on the reproductive tract, enabling it to rest in a more normal anatomic position. This surgery would be an adjunct procedure along with urethral extension, but would be required in only a minority of cases."
Look For Signs
While a number of causes for urine pooling have been described above, there is another factor that should not be overlooked, Easley and Trotter both note. That factor involves the overly lean or thin mare.
"One of the common combinations in urine pooling," Trotter says, "is a mare that has had a number of foals and is in poor body condition...A vital part of succeeding with these mares is to get them into the best physical condition possible with good nutrition and a regular worming program. If they stay skinny, you are not likely to win."
There are outward, telltale signs that can tip off the owner or farm manager to a urine pooling problem, Trotter says. If there is urine scalding or salts accumulating along the rear legs, the mare becomes an immediate suspect because these are signs of urine being dribbled from the vulva rather than evacuated in a normal, steady stream. A mare with a sunken anus, that sets abnormally forward of the vulva, is also a prime suspect.
Normally, a practitioner will first examine a suspicious mare with a speculum. In a number of cases, such an examination will yield a visual observation of accumulation of urine in the forward portion of the vagina.
Special laboratory techniques can ensure accuracy of a diagnosis. Most notable, according to Easley, is an examination of pH of fluid found in the fornix. Horse urine is slightly alkaline, but is usually more acidic when infectious agents are present.
When urine pooling is confirmed, it is time for a thorough examination, Easley notes. "A complete reproductive examination should be performed at this time to provide a basis for comparison after treatment is completed. A thorough reproductive workup should include assessment of ovarian function and serum hormone analysis, as well as a complete examination of the uterus--to rule out functional disturbances and the presence of periglandular fibrosis--including uterine culture, cytology of uterine contents, and endometrial biopsy.
"Hysteroscopy, or endoscopic inspection of the uterus, may be useful in evaluating the nature of the fluid and the lining of the uterus as well as checking for structures within the uterine lumen--cysts, exudate, tumors, and foreign bodies. Ultrasonographic evaluation of the reproductive tract can add information regarding texture and thickness of the uterus and presence and nature of fluid content within the tubular organs.
"In general, many infections and uterine inflammatory changes will be reversed or more easily treated after VVR has been successfully treated."
While surgery is the normal remedy in severe cases of urine pooling, there is one more treatment method that provides an alternative, at least in some cases--acupuncture.
Walter Zent, DVM, who is trained in acupuncture and is a practitioner with Hagyard-Davidson-McGee veterinary firm in Lexington, Ky., has used acupuncture in a limited number of cases and says he has experienced success.
"I have normally used it on mares about this time of year when you don't want to lose time to surgery," he says.
A month of the breeding season can be lost even if the initial surgery is successful, he explains, and longer if it isn't.
It is his belief that acupuncture helps tone up the muscles of the reproductive tract and that in so doing, the urethra orifice is moved into a more normal position, thus causing urine to be evacuated to the rear rather than refluxed forward.
If the mare doesn't settle during the first heat cycle, he says, the acupuncture procedure should be repeated during the next cycle. The number of treatments during a heat cycle, he says, would normally range from one to three.
Zent, whose practice primarily involves equine reproduction, says he has not used acupuncture on a large number of mares, but feels the procedure provides another treatment option.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
POLL: Rehabbing the Injured Horse