Low-volume uterine flush (n=401) was performed in 308 infertile mares to diagnose
endometritis. Mares evaluated were either barren after three or more breedings or
had two or more unsuccessful embryo recovery attempts during consecutive cycles. Culture
results were compared with cytological and histological findings, efflux clarity and
pH to substantiate that the micro-organisms recovered were truly pathogens. Cytological
specimens were evaluated for presence of epithelial and inflammatory cells, bacteria,
yeast and debris. Endometrial biopsies (n=110) were examined for the presence of neutrophils
in the stratum compactum. Micro-organisms were recovered in 282/401 (70%) of low-volume
flushes; E. coli was most frequently isolated (42.2%), followed by beta hemolytic
Streptococcus (37.6%). Efflux clarity of 318 flushes was clear (n=109), cloudy (n=149),
or mucoid (n=60). Isolation of micro-organisms was highly associated with cloudy and
mucoid effluxes (P<0.001), debris on cytological specimens (P<0.001), increased efflux
pH (P<0.003), and neutrophils on endometrial biopsy (P<0.01). E. coli was associated
with debris on cytological smear (P<0.002), whereas beta hemolytic Streptococcus was
associated with increased efflux pH (P<0.002). Using the presence of neutrophils in
a tissue specimen as the "best standard" for diagnosing endometritis, the sensitivity
of flush culture was 0.71 and for flush cytology was 0.8, whereas the specificity
was 0.86 and 0.67, respectively. Neutrophils in uterine flushes under-reported inflammation;
only 86/282 positive cultures were positive on cytology. The clinical estimate of
a contaminated (false positive) flush culture was 11%, if a false positive was defined
as positive culture with clear efflux and no debris or neutrophils on cytology (26/228).
In conclusion, a low-volume uterine flush was a rapid, accurate method for identifying
mares with chronic endometritis. When micro-organisms were recovered, endometritis
was confirmed by efflux clarity, pH and cytological findings of debris, bacteria,
or neutrophils. E. coli was most commonly isolated and it appeared to differ in pathogenicity
from beta hemolytic Streptococcus.