We’d all like to think that a mare’s womb is a warm, dark, nurturing environment perfect for transforming a small fertilized egg into a healthy foal in 340 days. According to equine reproductive specialists, however, uteri can be lined with bacterial "biofilm" containing millions of antibiotic-resistant bacteria in a glutinous, jellylike substance that in some cases can prevent mares from conceiving, much less carrying a foal to term.

One of these specialists presented an alternative to traditional antibiotics for treating endometritis–or inflammation of the uterine lining–at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas. Endometritis can occur post- breeding in reproductively normal mares or those with structural abnormalities of their reproductive tracts that allow bacteria to enter the uterus. In either case endometritis is an important cause of infertility in mares. Veterinarians usually treat it with antibiotics and by flushing the uterus, but in some mares this approach may not be sufficient to resolve the inflammation.

"The bacteria in the biofilm can be up to 500 times more resistant to antibiotics than the same type of bacteria grown in cultures in a lab, and many are also resistant to common antibiotics used in practice. Equine veterinarians therefore need to consider the use of ‘alternative’ methods to treat endometritis in mares rather than relying solely on traditional antibiotics to improve pregnancy rates and treat infertility," said Sara Lyle, DVM, PhD, Dipl. ACT, assistant professor of theriogenology in the Department of Veterinary Clinical Sciences at Louisiana State University’s School of Veterinary Medicine.