Associations Between Cytology/Bacteriology Findings and Live-Foal Rates in Broodmares 

To date, relationships between pre-covering endometrial swab cytology and bacteriology and fertility outcomes in Thoroughbred broodmares in the United Kingdom are unknown. These relationships could aid clinical decision-making. A retrospective cohort study investigated associations between cytology and bacteriology findings from the last endometrial swab taken in the breeding season (Feb. 15-July 15) and live-foal rates (predicted mean probability of producing a live foal) in Thoroughbred broodmares in the U.K. 

Research

Researchers extracted endometrial cytology and bacteriology findings from laboratory records for all last swabs submitted between 2014 and 2020. Mares’ status, age, and foaling outcome were collected from publicly available data sources. The researchers estimated live-foal rates for reported categories of cytology and bacteriology findings using a multivariable logistic regression model with mare and farm fitted as random effects, while adjusting for mares’ age, status, number of previous swabs submitted in that season, and any interactions. Pairwise comparisons with Bonferroni correction evaluated between-category live-foal rate differences. 

Data were available from 7,691 last swabs from 3,579 mares on 196 farms. In contrast to other categories of isolate, mares with a profuse growth of Escherichia coli  had significantly lower (p = 0.005) live-foal rates (59.1%; 95% confidence interval (CI) 43.7–74.5) compared to those with no growth (80.9%; 95% CI 79.2–82.6).  

There was interaction between mares’ age and cytology. In mares older than 12, the researchers observed significant reductions in live-foal rates (p < 0.05 in pairwise comparisons) between mares with > 30% polymorphonuclear:endometrial cells/high power field at cytological examination and mares with ≤ 0.5% PMN, a finding absent in mares 12 years and younger. 

Bottom Line 

These results highlight complexities veterinarians should consider when interpreting endometrial swab cytology findings. They also highlight the subset of mares with a profuse growth of E. coli, in which knowledge gaps exist around the etiologies underlying their poorer fertility outcomes. 

https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.70086

Related Reading

• Responsible Use of Antibiotics in Equine Reproduction
• Warmblood Fragile Foal Syndrome’s Effects on Pregnancy Loss
• Are Nontraditional Treatments for Equine Endometritis Effective?

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