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Bacterial culture and endometrial biopsy remain the best ways to diagnose inflammation of the uterus, also known as endometritis. Despite the availability of these diagnostics, the expense, specialized equipment, and time to obtain results may preclude their use. In some cases, when an immediate treatment decision must be made, an alternate strategy for diagnosing endometritis would benefit mares, potentially improving conception and pregnancy rates.

“In cows, research shows that a commercially available urine test strip that measures leukocyte esterase is an effective on-site test for diagnosing endometritis. This test can be used in lieu of cytology, which involves microscopically examining a swab of the lining of the uterus to look for white blood cells,” explained Catherine Whitehouse, M.S., a Kentucky Equine Research nutritionist.

Previous studies reported that mares with a higher number of white blood cells, also called leukocytes, have lower pregnancy rates (23-49%) than those with fewer leukocytes (60%).

Leukocyte esterase is an enzyme produced by leukocytes that can be measured to assess the presence of white blood cells in the uterus. While useful in cows, this test had not yet been validated in horses until researchers used urine test strips to measure leukocyte esterase in 46 client-owned mares from 14 farms in central Kentucky. The mares were examined as part of routine breeding management or as infertility treatment.

“The results showed that leukocyte esterase was negative in 80.4% of examined mares, correlating with a low number of leukocytes observed on microscopic analysis of a uterine tissue sample,” shared Whitehouse.

A positive and significant relationship between leukocyte esterase and identification of white blood cells on cytology was noted. This means that as the number of white blood cells noted on microscopy increased, so did the measured leukocyte esterase.

“To our knowledge, this is the first study examining the use of leukocyte esterase to detect endometritis in mares,” wrote the researchers. “Based on these results, we suggest that severe cases of endometritis can be detected using leukocyte esterase, as the test could be used to rule in endometritis in severe cases but not sensitive enough to rule out endometritis.”

 The difference in ruling in and ruling out disease involves the number of false positive and false negative results associated with testing, referred to as sensitivity and specificity.

For improving various aspects of reproduction, including some forms of endometritis, consider adding omega-3 fatty acids to your mare’s ration. Omega-3 fatty acids exert natural anti-inflammatory effects and help boost the immune system. Kentucky Equine Research offers EO-3, a marine-derived oil with high levels of both DHA and EPA. This product can be top-dressed onto feed.

“For optimal benefit, start supplementing mares with omega-3 fatty acids about 60 days prior to the anticipated foaling date,” Whitehouse recommended.

*Kelley, D.E., M.R. Schnobrich, S. Gayer, et al. 2019. Leukocyte esterase reagent strips for stall-side diagnosis of endometritis in mares. Journal of Equine Veterinary Science 81:102672.

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