Screening for Taylorella equigenitalis in Equine Semen: An Exploratory Study.
Authors: Mawhinney Ian, Davis Nicky, Carson Therese, Torrens Nicholas, Wales Andrew
Journal: Journal of equine veterinary science
Summary
Taylorella equigenitalis (contagious equine metritis organism) represents a significant breeding soundness concern, yet optimal laboratory screening protocols remain poorly defined. Mawhinney and colleagues compared culture versus quantitative PCR sensitivity using semen samples from two stallions artificially spiked with CEMO at 7 and 23 days post-ejaculation across serial dilutions, testing both raw and extended semen. Culture proved superior for fresh raw semen, detecting CEMO at all dilutions, but extender dramatically reduced bacterial recovery by two log cycles; critically, PCR detection failed three logs earlier than culture in fresh samples, though PCR performance remained consistent regardless of extender use and was unaffected by semen age. The estimated PCR detection limit of 10⁴–10⁵ cfu/mL aligns with reported natural CEMO concentrations in infected stallions, though bacterial overgrowth contamination compromised culture reliability in aged samples. For practitioners, this suggests culture remains the gold-standard screening method for fresh semen where contamination isn't problematic, whilst PCR offers a more robust alternative when semen age or microbial competition is anticipated—yet neither technique should be considered foolproof in isolation, and protocol selection warrants consideration of individual stallion circumstances and storage conditions.
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Practical Takeaways
- •PCR is more reliable than culture for detecting CEMO in extended semen and aged samples, making it the preferred screening method in routine stallion fertility assessments
- •Culture-based screening may miss CEMO infections in extended semen or older samples due to extender effects and commensal organism overgrowth
- •Practitioners should be aware that detection sensitivity varies significantly depending on semen handling (raw vs. extended) and age, which affects screening protocol selection
Key Findings
- •Culture detected CEMO in 7-day raw semen at all dilutions, but extended semen showed two log cycles lower counts and near-undetectable results at maximal dilutions
- •PCR sensitivity was unaffected by extender use, but for 7-day raw semen showed abrupt decline three log dilutions earlier than culture
- •Culture failed to detect CEMO in three of four 23-day semen samples due to commensal overgrowth, while PCR performance remained consistent
- •PCR detection limit estimated at 10⁴-10⁵ cfu/mL, consistent with typical CEMO concentrations observed in naturally contaminated stallion semen