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Infertility in Horses: Causes and Treatments

by Kristen Robertson, Immunall Herbal Horse Supplements from Sheridan Creek Tack

One of the greatest challenges in working with horses arises when it comes to breeding. Breeders spend thousands of dollars on getting their mares in foal, so when a mare fails to settle or manages to conceive but then aborts, it's not only the mare's health that's at stake. Equine researchers pay a great deal of attention to breeding problems, with one result being the availability and relative affordability of shipped cooled semen, so that even small operations can afford to shop around for the best studs for their brood mares
Breeding problemsólow sperm count or motility or poor sperm morphology for studs and various health issues for maresócan turn an attempt to breed your favorite mare into an ongoing battle with nature. Many people turn to reproductive technology; hormone injections, special rigging for live cover, sedatives or even surgery, to get a mare into foal. Before deciding the treatment, your vet needs to make a diagnosis. (Before attempting to breed any mare or stallion, you should have your animal's reproductive system examined by your veterinarian. This can help prevent later problems by making you aware of them from the beginning. And sometimes there are issues so big that your vet will advise you not to breed your horse at all.) When your mare cannot conceive or hold or your stallion isn't measuring up, one of the following breeding problems may be at fault:
Problems of Conformation

Cervical Incompetence, or 'Maiden Cervix'
A mare that hasn't been bred before may have a problem called "maiden cervix", in which the cervix so tightly closed that the excess seminal fluids can't be properly drained away after mating. Fluid that is retained causes inflammation and, if untreated, creates an acidic environment which soon becomes an infection. Mares with maiden cervix have been treated with antibiotics when they are mated, and also receive lavage (internal cleansing) after breeding. Ringer's solution is introduced vaginally and allowed to drain away, with the treatment being repeated several times, until the draining liquid is clear. Vets may administer the hormone Oxytocin, which promotes uterine contractions, in order to help the mare's body clear the foreign matter.

One of the more common problems with mare conformation is an oddly shaped vulva, which doesn't seal properly, exposing the uterus to contamination. Poor vulvar conformation can result in a condition called pneumovagina, in which air is pulled into the vagina, along with bacteria. Poor conformation can also result in fecal bacteria moving into the vaginal area. The bacteria proliferate, infection sets in, and what started out as a mechanical problem can become a long-standing infectious ailment that renders mares infertile. Veterinary surgeons have attempted to treat the condition causing pneumovagina by Caslick operation; a procedure that reduces the size of the vulvar orifice, but some studies have shown no particular effect on fertility, likely because the infection persists after the surgery. The common treatment is to give the mare antibiotics to treat the infection and to prevent further reinfection by means of the corrective surgery.

Indirect Issues
When a horse has particular issues with conformation of body, legs, head or mouth, there will always be a question as to whether the horse should be bred at all, even if actual conception is possible. Start the process with a complete physical before deciding to breed.

Looking at the available research, it's apparent that the primary problem in getting mare in foal and getting healthy foals at the end of the pregnancy is the condition called endometritis.

Endometritis is the general term given to any inflammation of the uterine lining, but there are different kinds of endometritis brought on by different conditions or organisms.

Fungal Endometritis
One of the drawbacks to using antibiotics is the fact that they wipe out good and bad bacteria, leaving the animal without natural protection against further bacterial or fungal invasions. The most common fungi in fungal endometritis in horses include the Candida (yeast) and Aspergillus (mold)ó that proliferate when the natural immune system has been weakened after antibiotic use. Fungal endometritis can be passed from stallion to mare, and unfortunately, there are no noteworthy cures as yet. Management of fungal endometritis relies primarily on reducing the sheer numbers of fungi through lavage using diluted vinegar, Betadine or DMSO.

Bacterial Endometritis
Much better known is bacterial endometritis, which has already been mentioned in the discussion of conformation problems. Bacterial endometritis may be the most common complaint in infertile mares. Dr. Angus McKinnon, and expert in horse health, names it as one of the major reasons that mares don't settle, or conceive but then slip the foal.

Bacterial endometritis is probably also the main cause of infertility in older mares who have foaled before. Acute infectious endometritis may be the result of impairment of the normal uterine defense systems, which may break down over time. Degenerative fibrosis may be a result of normal aging processes, or it may be the end product of a lifetime of reinfection: in either case, the scarring of the uterine lining causes infertility in older mares. Although some attempts have been made to surgically repair the uterine lining, adhesions are entirely too possible, and conception will still be an impossibility.

In a related problem, weakened reproductive structures may caused urine pooling, a condition in which mares do not void urine completely, particularly during estrus. The retained fluid can cause inflammation, and prevent conception.

Breeding Induced Endometritis
Along with mares with Maiden Cervix, some mares may suffer inflammation and subsequent infection as a direct result of breeding. The treatment is the same as that for Maiden cervix, since it seems to be a problem with fluid retention. However, there are also management issues that can help prevent breeding induced endometritis. It seems that mares that are bred on the foal heat are more disposed to developing infection, perhaps because of the wear and tear of the recent foaling. Multiple attempts at breeding in a single heat can also increase the chances of endometritis.

In this condition, the mare manages to get in foal, but the foal is aborted. Placentitis is an infection of the placenta; it may be introduced through the shared blood supply or may work its way from the cervix into the uterus. Testing for placentitis and a regime of antibiotics during pregnancy can prevent abortion, but a majority of foals lost in late term pregnancy may be attributable to placentitis.

Equine Arteritis Virus (EAV) infection is known to affect reproduction in mares and stallions, causing abortion after the third month of pregnancy or the death of foals after birth.

Contagious Equine Metritis (CEM) is a venereal disease of horses caused by the bacterium Taylorella equigenitalis, which is carried by stallions and causes infertility or abortion in mares.


Fescue Toxicosis
Foals born very weak or dead may be so because of fescue toxicosis, which occurs when mares in foal eat fescue containing fungal endophytes.

Results of Overwork or Stress

Loss of Libido
One veterinarian estimated that, in looking back over the thirty years of his practice, stallions that had once been bred to thirty mares in a season are now often expected to service closer to 300. Too frequent breeding or collecting can cause stallions to lose their libido, making breeding and collecting more difficult and lowering the overall quality of collected semen.

Bad breeding experiences, travel, hormonal issues like PMS or distress from non-reproductive ailments can all stress your horse. Stress affects the hormones needed for healthy breeding and settling; in fact, you may not be able to breed a horse at all if the animal is stressed. Proper management and good nutrition can help ward off stress related illness.

Other Problems
Other obstacles to easy breeding include hormonal problems, which may range from true pathology to management error, such as making mistakes about the mare's being in heat, or breeding off season without compensating with artificial light. The use of systemic antibiotics and arthritis treatment drugs have also been shown to negatively impact fertility. In stallions, testicular trauma or degeneration can cause damage sperm, and even the quality of the surrounding protein-rich fluid in semen can inhibit or promote sperm motility.

Support Fertility with Immune System Support Obviously, prevention is important in fertility: proper weight and nutrition, a basic check-up for potentially inhibiting ailments like laminitis, good breeding management and cleanliness all contribute to the health and fertility of your horse. Supporting your horse's immune system with an herbal supplement like Immunall can also have a positive impact on fertility. Immunall's all-natural ingredients regulate hormones, ease digestive processes, rebuild damaged cells, promote liver and kidney functioning and increase the production of infection-fighting cells in the body. Endometritis, a primary cause of infertility, is directly related to the body's inability to cope with bad bacteria and fungi as well as hormone-related issues preventing the prompt evacuation of excess seminal fluids after breeding. Helping the body fight bacterial and yeast infections while regulating normal hormonal fluctuations means healthier horses, higher conception rates and better birth rates. For testimonials from horse breeders, trainers and owners, go to .

Read the next horse breeding article on Foal Health Care.
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