Colloid Centrifugation as an Antibiotic-Free Alternative for Bacterial Reduction in Stallion Semen

Colloid Centrifugation for Semen - On left prior to centrifugation, on the right after centrifugation. Photo: Morrell et al.Routine antibiotic inclusion in semen extenders conflicts with responsible antimicrobial stewardship guidelines. Single layer centrifugation through a low-density colloid has demonstrated significant bacterial load reduction without compromising sperm quality. This controlled insemination trial assessed whether colloid-centrifuged antibiotic-free semen achieves comparable pregnancy rates to antibiotic-containing semen.

Study Design:

  • Pooled semen from 4 stallions divided into two treatment groups:
    • Control: standard extender with antibiotics (200 million sperm per dose)
    • Treatment: extender without antibiotics, centrifuged through low-density colloid, pellet resuspended antibiotic-free (200 million sperm per dose)
  • 46 pony mares: 23 per group; ovulation induced with human chorionic gonadotropin; inseminated 24 hours later
  • Pregnancy confirmed by ultrasound detection of embryonic vesicle at 14 days

Key Results:

  • Embryonic vesicle detected in 19/23 control mares (with antibiotics) and 17/23 treatment mares (colloid-centrifuged, no antibiotics)
  • No significant difference in pregnancy outcome between groups
  • No uterine infections developed in either group

Conclusions:

  • Colloid centrifugation effectively replaces antibiotics in semen extenders without reducing fertility or increasing infection risk
  • Findings support adoption of colloid centrifugation as a viable antibiotic stewardship strategy in commercial equine artificial insemination
  • Broader implementation could meaningfully reduce non-therapeutic antibiotic use in equine reproductive medicine

(Morrell J, Reigner F, Gesbert A, Barriere P, Laskowski D, Ntallaris T, Deleuze S. 2025. Centrifugation through a low density colloid as an alternative to antibiotics in semen extenders: a controlled insemination trial. Journal of Equine Veterinary Science 145:105309. https://doi.org/10.1016/j.jevs.2024.105309 – Presented in Association with and by Permission of the International Society for Equine Reproduction)