Embryo transfer induces a subclinical endometritis in recipient mares which can be prevented by treatment with non-steroid anti-inflammatory drugs

We tested the hypothesis that subclinical endometritis occurs after embryo transfer (ET) in the horse. Recipient mares were treated with meclofenamic acid (M) or flunixin meglumin (F) after ET or were left untreated (n = 9 per group). Embryos were re-collected 4 days after transfer. Endometrial biopsies were taken for histology and analysis of cyclooxygenase-2 (COX-2) by immunohistochemistry and for PCR. Bacteriological swabs were collected from the uterus and lavage fluid of donor and recipient mares. Progesterone and prostaglandin F_2α release was analysed in recipient mares after ET. Four days after ET, four embryos were recovered from group M and three from group F and untreated mares, each. The number of polymorph nuclear neutrophils was reduced in treated mares (p < 0.05). Expression of mRNA for inflammatory cytokines did not differ between groups. In group M, expression of endometrial prostaglandin-E-synthase was higher than in group F (p < 0.05). Three out of nine control mares unterwent preterm luteolysis (p < 0.05 vs. treatment groups), prostaglandin release (p < 0.05) and the number of COX-2 positive cells (p < 0.01) were significantly higher than in treated mares. Only few bacteriological swabs were positive. In conclusion, treatment of embryo recipient mares with non-steroid anti-inflammatory drugs inhibits the inflammatory response of the endometrium after ET. Meclofenamic acid may have advantages in comparison to flunixin meglumin due to a different influence on prostaglandin synthesis that may not result in inhibition of embryonic mobility.