Fertility trial of single layer centrifugation as an alternative to antibiotics in stallion semen extenders

Stringent efforts are required to stem the development of antimicrobial resistance, especially by avoiding non-therapeutic applications of antibiotics. One potential approach to reduce the use of antibiotics in stallion semen extenders could be to separate sperm from bacteria in the ejaculate physically by Single Layer Centrifugation (SLC) through low density Equicoll. The fertility of such samples was investigated in the present study. Conception rates were compared for control samples with antibiotics (n = 23) and Equicoll-prepared samples without antibiotics (n = 23). Bacterial loads before and after Equicoll-treatment were also assessed. Data were analysed with SAS software. The conception rates were not statistically different, being 19/23 for controls with antibiotics and 18/23 for Equicoll samples without antibiotics ( p = 0.71). Bacterial counts before and after SLC were 2566.7 ± 907.6 and 233.3 ± 137.8 CFU/mL, respectively. Slight uterine fluid accumulation was seen in 5 of the mares (4 in the control group with antibiotics and 1 in the SLC group without antibiotics), which was resolved by administering oxytocin. These results indicate that stallion semen can potentially be prepared without antibiotics by centrifugation through low density Equicoll, although a larger study is necessary to assess the microbiological safety and the lack of adverse effects in inseminated mares.