AAEP Convention 2005: Inflammation and Pregnancy Rates

Before heading to a breeding shed in Central Kentucky, most farms require all mares to have a clean uterine culture to look for bacteria. According to Thomas Riddle, DVM, a founder of Rood & Riddle Equine Hospital in Kentucky, uterine cytology (a microscopic examination of uterine cell types) provides a faster and more meaningful method to evaluate the health of the uterus.

Riddle and his colleagues performed a retrospective study that examined the relationship between uterine cytology, culture results, and Day 28 conception rates in 970 Thoroughbred mares bred during the 2001 to 2004 breeding seasons.

"We hypothesized that pregnancy rates would be decreased in mares that had moderate or severe inflammation on cytological specimens," Riddle said. "Furthermore, isolation of bacteria from uterine swabs would also result in decreased pregnancy rates if the cytological specimen had moderate or severe inflammation."

Riddle explained the data showed that both neutrophils (specific types of white blood cells found on cytology) and isolated pathogens were strongly correlated with pregnancy rates. "Pregnancy rates were significantly decreased for mares with positive cultures and positive cytologies," said Riddle. He explained that when looking at cytology results, "the degree of inflammation is more important to look at rather the just its presence.

"A positive endometrial cytology (indicating inflammation of the uterus) is a better predictor of reduced fertility than uterine cultures (indicating bacteria were present) alone," Riddle said. Almost twice as many (1.8 times) problem mares were identified by cytology assessment than by uterine culture. "It's important for veterinarians to examine both cytology and cultures for barren and foaling mares and repeat breeders," said Riddle.

The study's data also showed lower pregnancy rates in mares that had bacteria in the uterus but did not show inflammation. Riddle explained that inflammation could still be present in the uterus, but at a low level it might not be readily detected.

By doing uterine cytology, "mares with uterine inflammation can be identified more quickly than by uterine culture because samples can be processed and interpreted by laboratory personnel or by the veterinarian the same day the sample is taken (cultures take between 48 and 72 hours)," Riddle said. "Mares identified as having uterine inflammation can have additional diagnostics performed before breeding to determine the source of the inflammation."

He said that mares with uterine inflammation or bacteria isolated from their uteri have not only decreased conception rates, but are also at greater risk of pregnancy loss. "In future studies, we would like to look at long-term pregnancy maintenance rates in mares bred with positive cultures and cytologies," Riddle said.

Researchers for this study included Riddle; Michelle LeBlanc, DVM, Dipl. ACT; Scott Pierce, DVM; and Arnold Stromberg, PhD.

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for TheHorse.com .

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