27. Retrospective Evaluation of Ozone Uterine Lavage on Subsequent Pregnancy Success in Mares Affected by Post-Breeding Induced Endometritis

Abstract Post-breeding induced endometritis (PBIE) is one of the most common causes of reduced fertility in mares, often resulting in failure to conceive following artificial insemination. The use of ozone as an intrauterine therapy has been proposed as an alternative to conventional antimicrobial treatments due to its antimicrobial and anti-inflammatory properties. The objective of this retrospective analysis was to evaluate the effect of intrauterine lavage with ozonated lactated Ringer’s solution on subsequent pregnancy success in mares previously diagnosed with PBIE. Records from five mature, open, multiparous light-horse mares (age 8.8 ± 3.34 years; BCS 6.4 ± 0.25; mean ± SEM) were reviewed. During each breeding cycle, mares were induced to ovulate with deslorelin (1.25 mg IM) when a dominant follicle ( >35 mm), moderate uterine edema (grade 2–3), and a soft cervix were present. Mares were inseminated 24 hours after induction using semen from the same stallion. Ovulation and post-breeding uterine status were monitored, and pregnancy diagnosis was performed 14 days post-ovulation. Mares that were not pregnant after the initial insemination were short-cycled and, during the subsequent estrous cycle, received a single intrauterine lavage with ozonated lactated Ringer’s solution under the same reproductive conditions before ovulation induction and insemination. Retrospective pregnancy outcomes before and after ozone treatment were compared using McNemar’s exact test for paired binary data (pregnant vs. not pregnant) to account for repeated observations within mares, implemented in (GraphPad Software Inc.). Significance was set at P ≤ 0.05, with trends at 0.05 < P < 0.10. Following intrauterine ozone lavage, pregnancy was confirmed in all mares (5/5; 100%) compared with none during the previous insemination cycle (0/5; 0%). Using McNemar’s test on paired pregnancy status (before vs. after treatment), the continuity-corrected two-sided P-value was 0.0736, indicating a trend toward statistical significance. All mares not only failed to become pregnant after the first insemination but also developed post-breeding induced endometritis, characterized by intrauterine fluid accumulation and inflammatory cell infiltration. No signs of post-breeding endometritis were observed following uterine lavage with ozonated lactated Ringer’s solution. Given the small sample size and retrospective design, these findings should be interpreted cautiously; however, the consistent improvement observed across mares supports a potential beneficial effect of intrauterine ozone therapy and warrants further evaluation in a larger, controlled cohort.