Most donor mares in embryo transfer programs have impaired uterine clearance due to uterine and cervical problems. In addition, repeated breeding cycles, gynecological procedures, and embryo flushing make mares prone to endometritis. Anecdotally, pentoxifylline, an anti-inflammatory, has been used in mares to enhance blood flow in the reproductive tract and reduce uterine inflammation. However, this has not been critically studied. This study aimed to assess the post-breeding inflammatory response and embryo recovery of subfertile donor mares treated with pentoxifylline. This study hypothesized that pentoxifylline supplementation mitigates the post-breeding inflammatory response in embryo donor mares. Forty-two estrous cycles of seven embryo donor mares (16±3.7years old; 13±3years donating embryos) were completed in the study. In the first two cycles, mares received pentoxifylline (17mg/kg/day) given in 50mL of Broodmare-Plus® (Botupharma), the two subsequent cycles served as control, and in the last two cycles, mares received 50mL of Broodmare®. Mares were monitored daily, and then once a preovulatory follicle was detected, ovulation was induced with deslorelin (1mg, i.m.). Immediately before (0h), 24, 48, and 72h post-breeding mares had transrectal ultrasonography performed to determine ovulation, quantify uterine edema and intrauterine fluid accumulation (IUF). At similar timepoints, uterine cytology was collected, stained with Diff-Quik®, and polymorphous nuclear cells were counted in ten hpf. Embryo collections were performed eight days after ovulation, and mares receivedan injection of 5mg of dinoprost (i.m., Lutalyse, Zoetis, USA) to return to estrus. Statistical analyses were performed with Graph Prisma (San Diego, CA). Neutrophil counts were analyzed with ANOVA repeated measures and Tukey's as post-hoc. Edema scores and intrauterine fluid accumulation were analyzed with Kruskal-Wallis and Dunn's post-hoc. Embryo recovery rates were evaluated with Fisher's test. There was an effect of time for neutrophil counts in the washout cycle (P=0.032) but not in the other two groups (P>0.05). Neutrophil counts didn't differ across groups (P>0.05). Edema scores had effects of time (P=0.046) but no effects of group (P>0.05). Similarly, there was an effect of time (P=0.038) for IUF, and mares receiving pentoxifylline had reduced post-breeding IUF in comparison with washout cycles (P=0.034) but not different than the group receiving just Broodmare® (P>0.05). Embryo recovery was not different across groups (P>0.05) but remarkably different as follows: washout cycle was 29% (4/14); Broodmare® was 36% (5/14), and pentoxifylline (Broodmare-Plus®) was 57% (8/14). Mares in the study were subfertile older mares used as embryo donors for multiple years, thus, justifying the low embryo recovery for the cycles with no pentoxifylline. In conclusion, supplementation with pentoxifylline may be an alternative to improve the post-breeding uterine clearance. It may enhance embryo recovery in mares serving as donors for multiple years; however, this remains to be confirmed with a larger group number of mares.