Effects of intrauterine ozone insufflation in eleven subfertile mares: a case series

Equine persistent breeding-induced endometritis can lead to chronic uterine inflammation and fibrosis, reducing fertility. Intrauterine ozone (O₃) has recently been proposed as a potential treatment for mares unresponsive to conventional therapies. This case series describes O₃ treatment in eleven mares barren for at least one year despite multiple inseminations attempts. During the first oestrous cycle, low-volume uterine lavage and endometrial biopsy were performed, followed by 3 consecutive days of intrauterine O₂–O₃ gas insufflation. In the subsequent cycle, both procedures were repeated and mares were inseminated with fresh/fresh-cooled semen. Pregnancy was confirmed 14 days post-ovulation and was monitored until parturition. Ten/11 (90.9%) mares conceived and 9/11 (81.8%) delivered a live foal. Post-treatment biopsies showed a significant increase in CD163+ M2 macrophages, suggesting a positive influence of O₃ on endometrial tissue remodeling. These results suggest that O₃ therapy may contribute to fertility restoration in subfertile mares, but further studies are needed.