Impact of N-acetylcysteine infusion on detection of bacterial endometritis in mares

Endometritis is a leading cause of reproductive inefficiency, with endometrial mucus a potential contributor to this condition. N-acetylcysteine (NAC) has been harnessed as an anti-biofilm mucolytic agent. Hypothesizing that endometrial mucus may harbor bacteria and prevent their diagnosis through traditional methods, the outcome of NAC infusion on uterine culture and cytology results was investigated. Fifty-nine mares, barren from the previous breeding season, were presented for evaluation. On Day-0, one-liter of sterile lactated Ringer's solution was instilled into the uterus and collected back into the original bottle. Following this, each mare was infused with 3.3% NAC. A neat fluid sample was retained for turbidity analysis using a densimeter (ARS model 590a). The remaining lavage fluid was submitted for standard culture and cytology processing. The following day, each mare had the above lavage procedure repeated. On Day-0, 81% (48/59) of samples were cytologically negative, with 27% (16/59) cytologically negative the following day (Day-1). On Day-0, 63% of samples had no bacterial growth, 20% had scant growth, 10% had light growth, 7% had moderate growth, and none had heavy growth. On Day-1, these bacterial growth profiles changed to 31% no growth, 25% scant growth, 15% light growth, 24% moderate growth, and 5% heavy growth. Statistical analyses were performed using SAS with significance set to p<0.05. Turbidity values were reported in million cells/mL. A threshold value of 50 million cells/mL was established as a cutofffor negative (below 50 million cells/mL) or positive (above 50 million cells/mL). Densimeter result was significantly associated with culture result, with 100% of those mares displaying an increase in densimeter reading from negative to positive also having an increase in culture grade (p<0.01). If densimeter reading remained negative on Day-0 and Day-1, only 36% of those samples had an increase in culture grade (p<0.05). A strong association between lavage turbidity and bacterial growth was found, making this a potential adjunct diagnostic tool, especially in clinical settings with limited opportunities for performing cytology and a need to be selective of which samples are submitted for culture. By no means is this method proposed as a replacement for cytology and culture. Forty-eight mares had a negative cytology and no or scant bacterial growth on Day-0. These mares would reasonably have been designated “clean” by a practitioner based on these results. However, following NAC infusion, 17 of these mares (35%) displayed an inflammatory cytology and increased bacterial growth. Follow-up pregnancy results were available for 51 mares during the subsequent breeding season. All mares achieved 14-day pregnancy, with 57% (29/51) pregnant on the first breeding attempt. The authors thank the Hagyard Laboratory for their expertise and diligence.