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