Post-Insemination Infusion of Wharton’s Jelly Mesenchymal Stromal/Stem Cells-Derived Conditioned Medium: A Novel Approach for Improving Pregnancy Outcomes in Problem Mares

Simple Summary: Endometritis is the first cause of subfertility and the third most common disease affecting horses. The inconsistent effectiveness of traditional therapy and the rising incidence of antimicrobial resistance have heightened interest in alternative approaches. Therapies with Mesenchymal stem cells and their derivatives are increasingly recognized as promising options for treating uterine pathologies due to their immunomodulatory and antimicrobial properties. This study explored the possibility of treating problem mares with a post-insemination intrauterine infusion of Wharton's jelly mesenchymal stromal/stem cell-derived conditioned medium, by evaluating its anti-inflammatory and antimicrobial properties, as well as pregnancy rates. Post-insemination therapy enhanced the anti-inflammatory response and the pregnancy rates, making them comparable to those of normal mares and higher than those reported for problem mares in the literature. In addition, although the elimination of bacteria was not observed 12 h after treatment, the successful pregnancy following this treatment suggests a potential antimicrobial role. Those findings lay the foundations for the establishment of new treatment protocols for uterine pathologies in mares and other species. Treating endometritis is one of the major challenges faced by veterinarians. The effect of post-insemination intrauterine infusion Wharton's jelly mesenchymal stromal/stem cell-derived conditioned medium (WJ-MSC-CM) on the uterine response and pregnancy outcomes in problem mares was evaluated in this study. The cycles of 12 problem mares were treated seven/eight hours after insemination with intrauterine infusion of 20 mL of WJ-MSC-CM (TRT) or non-conditioned Ringer's lactate solution (CTR). Before (PRE) and 12 h after (POST) treatment, an ultrasonographic examination and a low-volume flush (LVF) for efflux clarity evaluation and bacteriological and cytological analysis were made. Pregnancy diagnosis was performed at 14 days and confirmed at 60 days after ovulation. A decrease (p < 0.05) in polymorphonuclear neutrophils infiltration and a trend toward significance in LVF efflux clarity (p < 0.1) were observed in TRT cycles. The TRT (50%) had a higher pregnancy rate (p < 0.05) than CTR group (0%) at first cycle. Only a trend toward significance was observed comparing pregnancy frequencies between the two groups (CTR 12.5% vs. TRT 54.5%), the pregnancy rate of TRT cycles was comparable to that of normal mares (p > 0.05) and higher (p < 0.05) than that reported for problem mares in the literature. Post-insemination uterine infusion of WJ-MSC-CM in mares restores pregnancy rates to normal levels, by its anti-inflammatory effect.