Treatment with a plant-based sugar called mannose not only can cure but can prevent endometritis, a common uterine infection that makes mares infertile, an SIUC research team has found. The treatment should be a boon for the horse breeding industry.

"We use it with all the problem mares that we breed, and they've gotten pregnant every time," says Sheryl King, a professor of animal science who heads SIUC's equine science program.

Endometritis, an inflammation of the uterine lining most often caused by bacteria, costs horse owners big bucks. It's hard to get rid of and can be pricey to treat—10 days of specialized antibiotics can come to as much as $2,000—not to mention the downtime expense when a breeder mare fails to breed.

King's sugar treatment has been tested on three different bacterial strains, including the nasty, $2,000-to-treat-it variety. It works on all three, which combined account for an estimated 90 percent of endometritis cases.

Breeders can administer the treatment in two ways: They can mix a dab of mannose in a salt solution and flush the solution through the mare’s uterus, or they can add mannose to the semen extender they use in artificial insemination. (Extender keeps sperm viable for a longer time, increasing the chances of pregnancy.)

Used in the salt solution, mannose can keep inflammation-causing bacteria from clamping on to uterine tissue. If an infection is already underway, the sugar-salt mix can make the bacteria let go.

Used with semen, the results are a little more iffy. While a mannose-laced semen extender prevents infection from occurring in healthy mares, and does it without a drop in pregnancy rates, infected mares inseminated with that semen often fail to conceive. "What we found when we looked at it under a microscope was that both the sperm and the bacteria attached to the mannose, and all the sperm were trying to impregnate the bacteria," King says.

To treat her mares, King first uses the mannose-salt mix to flush out the uterus, then inseminates the mare with the mannose-containing semen extender. "It works every time," she says. (For most healthy young mares, preventive measures against endometritis are needed only during breeding, when the risk of outside bacteria being introduced into the womb is greatest.) 

While that double procedure involves a little extra work, King says it's worth it. By using mannose in semen, breeders can avoid extenders that traditionally contain antibiotics. This in turn may slow the evolution of "superbugs"—bacteria that have become resistant to antibiotics through overexposure.

King adds that  when horses develop endometritis, owners too often "start blasting with antibiotics" without knowing what kind of infection they’re facing. If the antibiotic isn’t an appropriate one, that not only wastes time, it also contributes to bacterial resistance and to chronic infections. Since mannose works even with stubborn and antibiotic-resistant infections, it’s a better option from the start, she says.

The idea for the treatment was proposed more than 10 years ago by Graça Dias, a doctoral student working with physiology professor Lynn Nequin. Several master’s students in animal science—Jennifer Crawford, Marcy Christiansen, Sarah Johnson-Wessels, Stephanie Speiser, Shanna Morgan, and Deena Young—also worked on the project over the years, as did Elaine Carnevale, a veterinary researcher now at Colorado State University. 

King and her colleagues began with lab studies of tissue samples in petri dishes. They experimented with different kinds of specialized sugars, different formulas and dosages, different bacteria, and different incubation times before finally moving on to animal studies. 

"Mannose was the sugar that worked on all the strains and was least expensive—about a dollar a gram," says King.

The team’s research findings were reported in the April 2000 issue of the American Journal of Veterinary Research. Horse owners can find directions for making the mannose solutions here.

The research was partially funded by the Illinois Council on Food and Agricultural Research (C-FAR) and by the Illinois Department of Agriculture Thoroughbred and Standardbred Breeders Funds.
 

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