“Post-breeding endometritis is a major cause of subfertility, affecting approximately 15% of mares,” said John Steiner, DVM, Dipl. ACT, of Hagyard Equine Medical Institute. “We know it’s a big problem, so we’ve tried an adjunct treatment to see if this would help.”

He and his colleagues recently examined the efficacy of Propionibacterium acnes, sold under the trade name EqStim, and found that it can be useful in treating mares with persistent endometritis so they can be successfully bred. He presented results of the study at the Hagyard Bluegrass Equine Reproduction Symposium 2006, which was held Oct. 18-21 in Lexington, Ky.

P. acnes is a type of slow-growing, nonsporulating, Gram-positive anaerobic bacilli (rod-shaped bacteria), and it’s known for causing acne in humans. EqStim is designed to stimulate cell-mediated immunity in horses with bacterial and viral respiratory infections, and veterinarians often use it as an adjunct to antibiotic therapy.

Steiner and his colleagues designed a randomized, double-blind, placebo-controlled clinical trial to evaluate EqStim and its effects on conception, abortion, and live foal rates. Twenty-three practitioners based in either Lexington or Ocala, Fla., participated in the two-year study that examined 112 mares. They administered either a placebo or EqStim intravenously to mares with endometritis (confirmed using uterine cytology indicating inflammation), on Days 1, 3, and 7 of the study, and they were bred within 30 days of the first treatment and were only treated on one cycle. The veterinarian could treat the mare in any other way he/she wished for endometritis