Can mares be classified as resistant or susceptible to recurrent endometritis?

To evaluate the efficacy of oxytocin as a treatment for persistent post-breeding endometritis, a large clinical study was performed using 1,267 mares. The aim of the study was to assess the effect of three different treatments on pregnancy rate in mares. All mares were bred and allocated, in strict rotation, to one of four treatment groups: 1) non-treated controls; 2) intrauterine infusion of broad-spectrum antibio ties; 3) intravenous oxytocin injection; 4) intravenous oxytocin injection followed by intrauterine antibiotics. Pregnancy status of mares was determined at 13-15 days and 27-30 days post ovulation using ultrasonography. The pregnancy rate of Group 4 (72%) was higher than that of Group 2 (64%; P < 0.01) or Group 3 (63%; P < 0.01). The pregnancy rates of Groups 2 and 3 were similar (P > 0.80) and higher than that of Group 1 (56%; P < 0.01). Antibiotics and oxytocin appeared to have an additive beneficial effect which suggested two different modes of action of the combination treatment, namely antibacterial activity and fluid drainage. In non-treated mares more fluid accumulated in the uterine lumen after mating which was the most likely reason for the reduced pregnancy rates in this Group.