Association between post cover uterine lavage bacteriology and pregnancy rates in Thoroughbred broodmares in the United Kingdom

4 weeks, 29% (16/55; between every >4 and 8 weeks and 16% (9/55; 95% CI 9-28) every >8 weeks.Twenty-nine percent (16/55; 95% CI 19-42) of practices reported that their tanks had been critically low on nitrogen; 37% (6/16; 95% CI 18-61) were due to supply company failure to top-up tanks, 25% (4/16; 95% CI 10-49) to supply company failure to deliver, 19% (3/16; 95% CI 7-43) to staff failure to top-up and 12% (2/16; 95% CI 3-36) to failure to shut lids.Main limitations: Selection, recall and social acceptability bias.Conclusions: Top-up intervals >4 weeks and reliance on nitrogen suppliers may increase critical incident risk.Additional industry guidance on operating procedures may be helpful to mitigate risks.