Infectious Endometritis in Mares: Microbiological Findings in Field Samples

Endometritis is a major cause of infertility and subfertility in the mare. Early diagnosis and identification of the pathogens involved in infectious endometritis are crucial to initiate correct treatments in time, in order to optimize fertility and reduce the risk of bacterial resistance development. In this retrospective study (from 2014 to 2018), 394 samples (uterine swabs and lavages) obtained from mares before breeding, regardless of clinical history of endometritis were analyzed. Our bacteriological procedure included the subculturing from the enrichment in Brain Heart Infusion Broth of the samples resulted negative after direct smearing. A total of 386 microorganisms were isolated from 230 positive samples (58%). At least one microorganism was isolated from 33% of the samples after direct smearing and from another 25% after enrichment. The results, obtained from both direct smearing and enrichment, also show a significative difference between positive uterine lavages (80%) and swabs (53%). The most frequently isolated bacteria were α-haemolytic Streptococcus (27%), Escherichia coli (27%), β-haemolytic Streptococcus (26.1%) and Staphylococcus spp. (19.1%). In monoculture, the most common isolated microorganisms were α-haemolytic Streptococcus (13%), Staphylococcus spp. (12.2%), β-haemolytic Streptococcus (11.4%) and Escherichia coli (9.8%). Focusing on the samples with a pure culture, Gram-negative bacteria grew preferably after direct smearing, while Gram-positive after enrichment. In conclusion, the present study shows that uterine lavage with high volume of fluid statistically significantly increased the sensitivity of the bacteriological examination and highlights the key role of the enrichment step in the routine bacteriological laboratory procedure by increasing the isolation rate.