NATURAL BIOACTIVE COMPOUNDS AS SUSTAINABLE ALTERNATIVES TO ANTIBIOTICS IN BOAR SEMEN EXTENDERS: A PRELIMINARY STUDY ON SERRATIA MARCESCENS CONTAMINATION

Serratia marcescens contamination of extended boar semen for artificial insemination represents a serious threat to sperm quality and sow fertility due to its high resistance to antibiotics. This study investigated the antimicrobial effect of a boar semen extender containing natural bioactive compounds compared to a conventional antibiotic extender. Raw semen samples of three boars from the University of Veterinary Medicine Hannover, Germany, were split and extended to 20 × 10⁶ sperm/mL in four groups: (1) extender with natural bioactive compounds (Medi Bio Active; MediNova, Italy); (2) base extender without antimicrobial compounds (negative control 1); (3) conventional antibiotic extender as positive control (Formula5, MediNova, Italy); and (4) Beltsville Thawing Solution (BTS) without antibiotics (negative control 2). Samples were inoculated with mixed bacterial species to 5 × 102 CFU/mL and stored at 17 °C in the dark. S. marcescens growth was monitored on blood agar at 24, 48, 72, and 144 hours. Sperm progressive motility was assessed by Computer-Assisted Sperm Analysis – CASA (Androvision, Minitube, Germany). Sperm with intact plasma membrane and acrosome were evaluated through flow cytometry (Propidium iodide-negative, PNA-FITC-negative). After 24 hours, the extender with natural bioactive compounds showed no significant differences compared to the antibiotic-containing control (p = 0.58) in suppressing S. marcescens growth. Over time, the extender with natural bioactive compounds maintained bacterial levels under 3 CFUlog10/mL ± 0.33 for up to 72 hours. CASA analysis in samples spiked with mixed bacteria revealed that the average sperm progressive motility was 70% in the natural bioactive compound-containing extender group until 144 hours, while average values with the other extenders dropped below 65%. Plasma membrane and acrosome integrity was above 80% up to 144 hours in all extenders. These preliminary results suggest that natural bioactive compounds preserve semen quality and represent promising and sustainable alternatives to antibiotics in boar semen extenders.