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

: 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.