The equine uterus, in a manner of speaking, could be compared to a house. When a house is snug and solid with no broken windows, holes in the roof, drafts, or plugged drains, it is a comfortable place in which to live. If, however, there are defects that compromise the structure, we lose the comfort factor and must repair it if we are to once again have an abode that will properly shelter us.
So it is with the equine uterus. When all aspects are healthy and unimpaired, the uterus serves as a safe, comfortable "house" for the fetus. When it is compromised as the result of infection, cysts, scar tissue, and/or adhesions, however, the uterus can lose its capability to safely house the growing fetus. In fact, the uterine environment might even deteriorate to the point where the mare is unable to get pregnant.
When defects show up in a house, we use whatever means necessary to remedy the problem. The same is true of an equine uterus that has defects, only the tools used often are more state-of-the-art than the hammer or saw that might be used to repair a problem roof.
To diagnose the uterine problem, practitioners have at their disposal such sophisticated tools as the flexible fiberoptic endoscope with which to perform a hysteroscopy (a visualization of the structures within the uterus). And, when the problem is diagnosed, they can call into action a "Star Wars" type of weapon involving the laser beam (see laser article on page 28).
Before we get into diagnosis and treatment, though, it would be good to understand the uterine cyst, an affliction that can attack the "safe house" environment of the uterus. The uterine cyst can be described as an obstructed and dilated lymphatic channel.
Normally, says Scott Bennett, DVM, of Equine Services, a clinic and hospital in Simpsonville, Ky., and who is deeply involved in the reproduction field, the cysts will develop in the older mare after a number of pregnancies. Rarely do they show up in the young mare unless she has a history of chronic endometritis.
Older mares with a history of multiple pregnancies and births, says Bennett, often develop scar tissue within the uterus. The scar tissue can cause a clogging of channels in the lymphatic drainage system. This means there is literally a backup of fluid at these locations.
The fluid is secreted by glands within the uterus with the correct levels being maintained via drainage through the uterine walls. Problems can arise when uterine scar tissue clogs portions of this drainage field. The result is a cyst or cysts filled with fluid.
"A few cysts within the uterus won't make that much difference, unless they are large," says Bennett. "Their ability to compromise the functioning of the uterus is dependent both on their size and number. Normally, I don't worry about two or three small cysts, but one big cyst can become a major problem.
"In some mares, there will be 10 or 12 cysts, and their presence in that number will definitely cause problems even though they may not be large. The cysts become physically obstructive, sometimes preventing semen from entering the uterus and, if a pregnancy does occur, can compromise mobility of the embryo. That's how the embryo codes in--giving the signal that a pregnancy has occurred--by wandering through the uterus the first 18 days."
When cysts are suspected, it is time for a thorough uterine examination, Bennett believes. One of the first approaches, he says, is the hysteroscopy with the flexible fiberoptic endoscope.
It is important, he explains, to determine the overall health of the uterus, rather than just finding out whether cysts exist, in order to come up with a more valid diagnosis as well as prognosis concerning a future pregnancy.
If, for example, cysts are removed and the uterus is otherwise healthy, the chances of obtaining a pregnancy that will be carried to term are excellent. If, on the other hand, the uterus is afflicted with infection or has massive scar tissue and adhesions, simply removing cysts won't totally solve the infertility problem.
Bennett explains examination via the hysteroscopy procedure this way: "The mare's rectum is evacuated and the vulva and perineal area prepared aseptically. Insufflation (inflation) of the uterine lumen may be done with filtered air, carbon dioxide, or fluid. Filtered air or carbon dioxide is my preference, as fluid often will cloud with suppurative (producing pus) endometritis, making the exam more complicated. Early estrus or post-estrus is preferable because insufflation is difficult when the cervix is open during estrus.
"The structures that can be examined (via hysteroscopy) include the cervix, endometrium (uterine body and horns), uterine bifurcation, and tubal uterine junctions. Abnormalities easily seen include infections, cysts, scar tissue, adhesions, and tubal uterine junction pathology.
"It is important to take an overall view of the uterus before insufflating the uterus entirely. Insufflation will tend to flatten and blanch the endometrium. Also, insufflation resistance is a good indication of uterine tone. The uterus that dilates easily without any resistance often indicates deep uterine pathology."
"By far," says Bennett, "one of the most beneficial methods of evaluating the endometrial integrity is with the endometrial biopsy. It helps map out the uterine endometrial integrity and helps us evaluate what percentage of the uterus is pathological. This is important because early embryo migration and endometrium interaction establish recognition of pregnancy. In my experience, a reduction of 25% viable endometrium will greatly reduce the embryo-endometrium recognition factors and leave a predisposition to early embryonic death. Likewise, loss of endometrial integrity also reduces the proteins necessary for embryonic nutrition and maintenance."
The scar tissue that can stimulate the development of uterine cysts is often the chief culprit in compromising the safety factor of the uterine "house." Unfortunately, fibrosis or scar tissue that develops within the endometrium as a consequence of inflammation or advancing age is usually considered a permanent and irreversible change within the uterus lining.
"When we start seeing scar tissue in more than 30% of the uterus," says Bennett, "we then consider that mare in the subfertile class. At that point, you have to make a real effort to get her pregnant, and, more importantly, to maintain the pregnancy."
Bennett estimates that 20-25% of the broodmare population falls into the "problem" category.
In most cases, the scar tissue is a result of the wear and tear on the uterus because of multiple pregnancies, which have an eroding effect on the reproductive tract.
Patrick McCue, DVM, PhD, Diplomate American College of Theriogenology, of Colorado State University, describes a grading system to help determine the overall health of the uterus and the potential for it to serve as a "safe house" for the fetus.
"The endometrium," he says, "is classified on a I to III grading scale based on biopsy characteristics. Grade I endometrium is essentially normal, with minimal inflammation or fibrosis. Grade III endometrium includes severe inflammatory and/or fibrotic changes. Grade II is a broad category encompassing all pathologic levels in between Grades I and III."
McCue goes on to provide an expected foaling rate by percentage for each of the categories. For Grade I, he says, where the "degree of endometrial change" is absent, the expected foaling rate by percentage runs from 80 to 90. For Grade II A, where the degree of endometrial change is mild, the expected foaling rate is 50-80%. For Grade II B, where the degree of endometrial change is moderate, the expected foaling rate is 10-50%. For Grade III, where endometrial change is severe, the expected foaling rate will fall below 10%.
If the hysteroscopy exam and uterine biopsy reveal that, though there are cysts present, the uterus is otherwise normal and healthy, the prognosis is usually excellent for both achieving a pregnancy and for the fetus to be carried to term, providing the cysts are small and few in number. The prognosis is also excellent if more numerous and larger cysts are removed.
"The laser has been absolutely a godsend," says Bennett. "A lot of the uterine cysts are high up in the horn and you have to literally go around a corner to get to them. That is difficult to do with a traditional straight instrument."
The procedure is much simpler with the laser fiber, which is carried within an endoscope that is inserted into the uterus via the vagina. This approach allows the practitioner to visualize the interior of the uterus, locate the cysts, and literally vaporize them.
Bennett recommends the contact laser rather than the non-contact. This means the laser must literally be in contact with the cyst before it is activated. This provides an element of safety, he believes, over the non-contact laser that need not be in contact when activated. If the mare should move as the non-contact laser is activated, Bennett explains, it could miss its cyst and cause uterine damage.
With the contact laser (the Nd:Yag laser), a hole is first opened in the cyst to drain the lymphatic fluid.
"The laser will not only poke a hole in the cyst and drain it," Bennett says, "but as the cyst shrinks, the laser will continue to deliver energy and it seals the cyst so it doesn't come back. Often, in the other procedures where you literally cut out the cysts, they have a tendency to come back."
Not only is the laser treatment effective, it is fast.
"With the laser, we can clear five to six uterine cysts in eight to 10 minutes," says Bennett.
Some of the cysts encountered, he said, are huge. "We had one mare referred to us that had twice been ultrasounded as 45 days pregnant. Instead, she had a huge cyst."
The cyst was removed with the laser, he said, and the mare really became pregnant.
"The important thing," he emphasizes, "is to have a proper endoscopic examination and biopsy prior to treatment to diagnose that you have an otherwise normal uterus. If you have an otherwise normal uterus, the success rate (of removing uterine cysts) is near 90%."
While the most common cyst is the one that results from clogging a portion of the lymphatic drainage system, there is the rare glandular cyst. This, too, is treated with the laser, Bennett says, but is more difficult to deal with. Often, says Bennett, these cysts are a result of chronic endometritis.
Bennett underlines the fact that uterine cysts are only one of a number of problems that can result in a barren mare and emphasizes again that a thorough reproductive examination be performed in developing a prognosis.
"One of the most perplexing situations facing the equine practitioner today," he concludes, "is what to do with the problem broodmare. Often owners have spent large sums of money and devoted much time to breeding mares with reduced fertility. These owners deserve and desire a methodology to at least let them know what their anticipated success will be versus feeding, transporting, and maintaining a broodmare for another year. Certainly, the methodology is cheaper than maintaining a non-productive broodmare--in Kentucky this can cost $4,000 to $5,000 per mare per year. Given a viable statistical basis for success, the mare owner can then make an economic decision derived from an intelligent data base."
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: University Equine Hospitals