Dismount Semen Sample Evaluation, Post-Mating Antibiotics, and Mare Clinical Parameters

Background Purpose

Dismount Semen Sample Evaluation - microscope drip on slideIn Thoroughbred breeding, in-hand mating is the only permitted method, and dismount semen sample evaluations are routinely collected to confirm ejaculation and assess semen quality. Post-mating uterine antibiotic infusions (ceftiofur or ticarcillin) are commonly used to reduce infection risk. This study examined whether dismount sample characteristics are associated with mare clinical outcomes.

Methods

  • 25 mares, 50 matings, 3 fertile stallions
  • Ovulation induced with a GnRH-agonist; mares mated 24h later under sedation
  • Each mare underwent a control cycle (saline infusion) and an antibiotic cycle (ceftiofur or ticarcillin)
  • Uterine cultures, cytology, and daily ultrasound were performed for 6 days post-mating
  • Pregnancy was confirmed at 14 days then terminated

Key Findings

  • Dismount parameters (volume, motility) did not differ between control and antibiotic groups
  • Antibiotic treatment reduced endometrial leukocyte counts and uterine infection rates (40.5% vs. 54.2%)
  • Pregnancy rates were notably lower in antibiotic-treated cycles overall (36%) vs. controls (54%), driven largely by the ceftiofur group (25% vs. 75%)
  • Ticarcillin showed no significant difference in pregnancy rates vs. control

Conclusion

Dismount semen parameters were not associated with mare clinical outcomes. Surprisingly, despite lower infection markers, antibiotic-treated cycles — particularly ceftiofur — showed reduced fertility, raising questions about routine post-mating antibiotic use in Thoroughbred breeding.

(Magalhaes HB, Canisso IF. 2025. The associations between dismount semen evaluation, post-mating antibiotics, and mare clinical parameters. JEVS 145:105301 – Presented in Association with and by Permission of the International Society for Equine Reproduction)