Screening for Taylorella equigenitalis in Equine Semen: An Exploratory Study

The study examined and compared the sensitivity of culture and a quantitative PCR assay for screening equine semen for the presence of Taylorella equigenitalis (CEMO). Chilled semen samples, both raw and treated with extender, from two stallions were spiked with the organism at seven or 23 days postejaculation and prepared in serial dilutions. Culture of the 7-day raw semen readily detected CEMO at all dilutions, but extended semen yielded counts that were two log cycles lower at equivalent dilutions, with the organism being nearly undetectable at the maximal dilutions. By contrast, PCR sensitivity was not affected by extender, but for 7-day-old raw semen, PCR detection declined abruptly three log dilutions earlier than detection by culture. The more aged 23-day-old semen proved less satisfactory for spiking, with detection of CEMO by culture failing in three of the four samples due to overgrowth with commensal organisms. However, PCR performance was similar in both the 23- and 7-day spiking series. The detection limit by PCR is estimated at between 10⁴ and 10⁵ cfu/mL. Typical CEMO concentrations in the semen of colonized stallions are not widely reported but where natural semen contamination has been investigated, the organism was present at this order of magnitude. The reliability of detecting CEMO infection using semen samples by either method is discussed.