The study assessed the impact of four equine semen processing techniques on sperm quality and microbial load immediately post-processing and after 48 h of refrigeration. The aim was to explore the potential reduction of prophylactic antibiotic usage in semen extenders. Semen from ten adult stallions was collected and processed under a strict hygiene protocol and divided into four aliquots: Simple Centrifugation with antibiotics (SC+), Simple Centrifugation (SC-), Single-Layer Colloidal Centrifugation (CC-), and Filtration (with SpermFilter®) (F-), all in extenders without antibiotics. Sperm motility, viability, and microbial load on three culture media were assessed. No significant differences were observed in the main in the sperm quality parameters among the four protocols post-processing and at 48 h (p < 0.05 or p < 0.1). Microbial loads in Columbia 5% Sheep Blood Agar and Schaedler vitamin K1 5% Sheep Blood Agar mediums were significantly higher (p < 0.10) for raw semen than for CS+, CC-, and F- post-processing. For Sabouraud Dextrose Agar medium, the microbial load was significantly higher (p < 0.10) in raw semen compared to CS+ and F-. No significant differences (p < 0.10) were found in 48 h chilled samples. Regardless of antibiotic presence, the evaluated processing methods, when combined with rigorous hygiene measures, maintained semen quality and reduced microbial load to the same extent as a traditional protocol using antibiotics.
Keywords: absence of antibiotics; antibiotics-free extender; chilled equine semen; filtration; semen microbial load; simple centrifugation; single-layer colloidal centrifugation.