Sometimes it can be quite difficult to get a mare pregnant, especially if she has fertility problems. There are several reasons that a mare might be infertile, many of which can be treated. Two reproductive specialists from Lexington, Ky., shared their extensive knowledge of several of the problems that mares can face with attendees of the Thoroughbred International Exposition and Conference in Lexington, Ky., June 20-22.

Karen Wolfsdorf, DVM, Dipl. ACT, reproductive specialist at Hagyard-Davidson-McGee Equine Associates; and Michelle LeBlanc, DVM, Dipl. ACT, reproductive specialist at Rood and Riddle Equine Hospital, have specialized in reproduction since 1995 and 1982 respectively.  

Wolfsdorf began her presentation with the three natural physical barriers of the mare’s anatomy that help prevent contamination of the reproductive tract. The vulvar labia is the lip-like outer portion of the mare’s genitalia. The vulvovaginal fold, part of the the hymen, is a fold of mucous membranes found at the opening of the vagina. And finally, the cervix is the narrow opening at the beginning of the uterus. Compromise or failure of these barriers can cause particulate matter or air to enter (pneumovagina) to enter the reproductive tract. The resulting contamination could result in cervicitis (cervical inflammation), vaginitis (vaginal inflammation), or endometritis (inflammation or infection of the endometrium or uterine lining).

Conformation problems of the reproductive tract or changes over time, possibly as a result of multiple foals, can result in retention of urine in the vagina. This is called vesicovaginal reflux, or more commonly urine pooling. This problem results in reduced conception rates, changes in lumenal pH, periglandular fibrosis (formation of scar tissue), or inflammation.

Wolfsdorf said that mares which have had numerous foals usually develop poor reproductive conformation because of the loss of muscle tone and damage to the vulvar suspensory ligament, retractor muscle, and the vulvar constructor muscle. She said it is best to examine older mares when they are in heat since the effects of estrogen will increase the vascularity and relaxation of the muscles, giving the veterinarian a better picture of what problems might have to be dealt with before breeding.

Other less common causes of mares pooling urine an ectopic ureter, cystitis, and urolithiasis. An ectopic ureter is one in which the ureter (the tube that conveys urine from the kidney to the bladder) opens somewhere other than the bladder. Cystitis is inflammation of the urinary bladder, and urolithiasis is the presence of calculi, or mineral deposits, within the urinary tract.

Diagnosis of reproductive problems, specifically urine poolers, involves a reproductive exam, which can include a speculum exam (best done during estrus), uterine culture and cytology to check for inflammation and contamination, a biopsy for long-term prognosis, transrectal ultrasound for uterine fluid, and enzyme tests to check the fluid for changes in pH, creatinine levels, and urea.

Treatment will depend on the findings of the exam and various tests. For urine pooling, if the problem is mild and is caught early, then the urine can be removed and the horse’s physical condition can be improved to strengthen the muscle tone. In more severe cases, medical management is needed. This might include uterine lavage (flushing), use of the medications oxytocin or bethanecol, which might improve urethral sphincter tone (the opening of the urethra into the vagina), acupuncture, or surgery to extend the urethral sphincter closer to the opening of the vulva.

Another problem that Wolfsdorf said might cause infertility is fungal endometritis, which occurs when a fungus or yeast contaminates the uterus and causes infection and inflammation. She said this problem is hard to treat and has a high rate of recurrence. Causes can include poor vulvar conformation, repeated and/or lengthy intrauterine antimicrobial treatment, and excessive manipulation of the reproductive tract. The most common culprits are the Candida spp. and the Apergillus spp. Diagnosis of fungal endometritis can be confirmed with uterine cytology and culture, ultrasonography which reveals highly particulate fluid, and the presence of vulvar/vaginal discharge.

Treatment can involve uterine lavage with large volumes of fluid, the use of dimethyl sulfoxide (DMSO), diluted betadine or vinegar, or antifungal agents such as clotrimazole, amphotericin, fluconazole, and nystatin. Wolfsdorf said that the disadvantage to antifungal agents is that they are expensive and the duration that treatment is necessary is unknown. Despite treatment, prognosis might still be poor since treatment only affects certain stages of fungal development, the organism might have attached to the endometrial folds, or the mare might have delayed uterine clearance. The chance for re-infection is high as it is hard to destroy or flush out all of the organism.

LeBlanc focused her part of the presentation on problems of older mares. She said that 30% of mares over the age of 14 will need veterinary assistance to conceive. One problem older mares face is persistent follicles, or cystitic follicles. These follicles do not ovulate in response to the normal signal from the brain. These follicles will show up on an ultrasound as a black area with white strands, which indicates blood clots. (Normal follicles show up as all black areas on an ultrasound.)

LeBlanc recommends that breeders continue to tease the mare until she goes out of heat. Five to six days after she is out of heat, her progesterone levels can be measured. If they are between one and four ng/ml, then prostaglandin might help. If the progesterone level is less than one ng/ml, then there is no luteal tissues surrounding the cystic follicle and all one can do is wait for the mare to come back into estrus on her own. LeBlanc said these follicles do not respond to human chorionic gonadotropin (HCG) or the hormonal drug Ovuplant.

Human chorionic gonadotropin should only be used on follicles that are at least 35 mm, for the best response, since the follicle must be “sufficiently mature” before it will respond to HCG. It has been found that as mares get older, some do not respond to HCG.

LeBlanc explained that uterine inflammation is a normal process after breeding. The mare’s body treats sperm as a foreign object it should attack. After the attack, immune cells then engulf the sperm, and try to clear it from the body. All of this happens after 15-30 minutes, so any sperm that has not reached the oviduct during that time will be under attack.

Another problem of older mares is accumulation of fluid in the uterus. This could be due to decreased cervical drainage as the uterus loses the ability to contract properly, or due to decreased lymphatic drainage (which removes particulate matter and fluid swelling).  If treatment is started after too much fluid has accumulated, it’s hard to get rid of, said LeBlanc. Oxytocin can be used to produce uterine contractions for 20-40 minutes, four to six hours apart, which helps clear the fluid.
The prostaglandin cloprostenol (Estrumate) can produce contractions for up to five hours for clearance of fluid and a return to normal of the lymphatic system. LeBlanc warns against using cloprostenol longer than 12 hours after ovulation.

She said there is no magic bullet for treating infertility. “You must treat each mare as an individual, and it takes time, money, and diagnostics.”

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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