Post-breeding inflammatory response in mares susceptible to persistent breeding induced endometritis. Assessments were carried out from pre- (early onset of estrus) and post-breeding, and on the day of embryo flushing (eight days post-ovulation, D8): (A) Intrauterine fluid accumulation pre- and post-breeding; (B) mean polymorphonuclear cells (PMNs) assessed in five high-power fields (hpf) in endometrial cytology, and (C) mean PMNs counts assessed in five hpf in endometrial biopsies. Mares (n = 12) had estrous cycles (n = 34) assigned to receive four intrauterine infusions with Lactate Ringer’s Solution (Control, n = 12), platelet-rich (PRP n = 12), or -poor plasma (PPP n = 10) in a crossover design. Different superscripts denote the effects of time (a,b,c) and differences between groups (X,Y) (p < 0.05). Asterisk (*) denotes tendency (0.05 < p < 0.1).