Breeding the Problem Mare AAEP Discussion

Anytime veterinarians talk about breeding the problem mare, it always develops into a lively, animated discussion. The Table Topic on Breeding the Problem Mare was no different at the 2009 American Association of Equine Practitioners (AAEP) Convention in early December.

The audience was asked to list items for discussion, and many difficult-to-treat causes of infertility were addressed, including the cause and treatment of anovulatory follicles, management of mares with an incompetent cervix, successful yeast infection treatment, and biofilm and how it affects equine reproduction.

Anovulatory follicles are a broad term given to abnormalities of ovulation that result in an egg remaining trapped in the follicular cavity and not entering the oviduct, the site of fertilization. Anovulatory follicles are a menace to veterinarians and mare owners because the problem cannot be predicted and once it occurs, there is no method for inducing that particular follicle to ovulate.

Mares with the condition develop a normal-appearing dominant follicle on ultrasonography during estrus, exhibit classic signs of heat when presented to the stallion, but the follicle does not ovulate even after repeated treatment with an ovulatory agent such as hCG or deslorelin.

Recent research indicates that anovulatory follicles occur more commonly when mares are given prostaglandin on Day 9 to 11 of the cycle (Day 1 is the day after ovulation). They have also been noted to occur repeatedly in mares with chronic uterine infections. In both scenarios, follicular development is likely affected adversely because prostaglandin given either as an injection or by systemic release as a by-product of the inflamed uterus interferes with rupture of the follicular wall. Therefore, mares that are to be short-cycled for breeding should be given prostaglandin before Day 9 of the estrus cycle, and those mares that repeatedly produce anovulatory follicles without injection of prostaglandin should be evaluated for uterine infection.

An incompetent cervix can be defined as one that does not open properly during estrus or one that does not close properly during diestrus. The former is a common cause of infertility in mares that are not bred for the first time until they are 10 years of age or older. Mares with the condition are identified during artificial insemination and should be treated with uterine lavage and oxytocin or cloprostenol between 4 and 12 hours after breeding to assist in clearing the inflammatory by-products of insemination. If not treated, the mares will develop a persistent inflammatory response that will result in uterine irritation and death of the embryo when it enters the uterus on Day 6 after ovulation.

Other treatments that can be added to this therapy include dexamethasone or prednisolone given before breeding in order to decrease the severity of the inflammation that occurs in response to the foreign antigens on semen.

The cervix consists of smooth muscle, and if torn it heals with scar tissue or it might adhere to the vaginal wall. A cervix that does not close properly during diestrus results from a previous foaling or natural breeding trauma. These defects are best identified during diestrus, when the mare is under the influence of progesterone. Most must be repaired surgically if the mare is to carry a foal until term. If the defect is not repaired, mares can develop chronic uterine infections.

Yeast infections are not common except in a mare with an incompetent cervix, perineal conformation abnormality, or those that have been treated repeatedly with intra-uterine antibiotics. Treatments include repairing anatomical defects and infusion of antiseptics, which are lavaged out with lactated ringers or saline. In some cases mares will require treatment with anti-fungal agents for prolonged periods (10 to 21 days) in order to clear the infection. Affected mares that require prolonged treatment commonly have cervical incompetence.

The final topic discussed was biofilms, a substance produced by yeast, gram-negative organisms, and some gram-positive organisms that protect the organism from the host's immune response. These organisms live normally and uneventfully in the mouth and vagina unless the flora is disrupted. Once this occurs, there can be an overgrowth of certain bacteria within the uterus resulting in prolonged infection. Their importance to equine reproduction is that they confer antibiotic resistance. New treatment strategies have been developed and are used before infusion of intra-uterine antibiotics in mares with yeast, fungal, or chronic bacterial infections. Compounds that appear to be effective in removing biofilm include N-acetylcysteine and Tricide, a buffered chelating agent. These compounds appear to be safe when infused into the uterus, but more work is needed to determine their efficacy and appropriate dosing.

This Table Topic was facilitated by Kevin Hahn, DVM, and Michelle M. LeBlanc, DVM, Dipl. ACT, who wrote this report.

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