Uterine Ultrasound, Cytology Helpful in Pinpointing Pathogens (AAEP 2010)

When it comes to a mare's uterus, ultrasound examination and cytology (examination of cells under a microscope) can give a veterinarian a pretty good picture of what's going on inside that could be confounding conception. However, comparing these results to culture (testing of samples for pathogens) helped researchers on a recent study link specific bacteria with certain uterine signs, which ultimately could help veterinarians predict more accurately what pathogens could be at play in problem breeders.

Modesty D. Burleson, VMD, formerly an associate of Rood & Riddle Equine Hospital and presently the resident veterinarian for Spy Coast Farm in Lexington, Ky., presented this data at the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md. Burleson and colleagues performed a retrospective study to determine the relationships between micro-organisms isolated from the uterus, cytology findings, and ultrasonographic findings in Thoroughbred mares during estrus.

The team reviewed 670 positive endometrial culture samples from 410 Thoroughbred mares in Central Kentucky. Mares were examined by either Michelle LeBlanc, DVM, Dipl. ACT, or Tom Riddle, DVM. The corresponding cytology and ultrasonographic results from the reproduction examination were recorded to determine relationships between organisms and diagnostics tests. The cultures were obtained by either culture swab (453 cultures) or by small volume flush (217 cultures).

Burleson and her colleagues uncovered the following key findings:

  • Beta-Streptococcus and E. coli were the most common pathogens isolated on both the culture swab (28.3% of the time) and small volume flush (20.5% of the time);
  • Mares with intrauterine fluid (fluid in the uterus detectable on ultrasound, which is generally a sign of irritation, contamination, or infection) were 1.4 times more likely to have a moderate to severe inflammatory cytology than those with mild or no inflammation. Greater than five neutrophils (white blood cells capable of engulfing and destroying bacteria and other disease agents)per high power field under the microscope indicated severe inflammation;
  • Mares with positive cultures for Beta-Streptococcus, Klebsiella spp, and yeast were more likely to have intrauterine fluid present. Fluid was less likely to be seen when Enterobacter cloacae, E.coli, Staph aureus, Pseudomonas, two or more organisms, or non-pathogens (Bacillus, Micrococcus,or Alpha Strep) were isolated;
  • Mares with positive cultures for yeast, Klebsiella spp., Beta-Streptococcus, and non-pathogens were more likely to have a positive cytology with greater than 2 neutrophils per high power field; and
  • Moderate to heavy debris on cytology was more likely to be seen when, yeast, non-pathogens, E.coli, Beta-Streptococcus, or two or more organisms were isolated on culture.

Intra-uterine fluid was associated more commonly with a moderate to severe inflammatory cytology than with isolation of a specific micro-organism. The presence of intrauterine fluid, which is an indicator of inflammation, was most commonly associated with B-Streptococcus, E. coli. and other gram negative bacteria.

"Two of the common dogmas in the world of reproduction were found to be not true in all cases," Burleson noted. "First, a bacterial or yeast infection must be associated with intra-uterine fluid. And second, if bacteria is isolated on culture and the cytology is negative, the isolated is considered to be a contaminate."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.