Occurrence of ultrasonographic assessed placental abnormalities, treatments, pregnancy outcome, and subsequent fertility on a large warmblood stud farm: a retrospective field study.

Little is known about the incidence and outcome of high-risk pregnancies in equine practice and clinical studies on spontaneous occurring placentitis cases and treatments are missing. Therefore, the aims of this retrospective field study were to (1) describe the incidence and severity of ultrasonographic assessed placental abnormalities (UPA) in 4,192 pregnancies on a large commercial warmblood stud farm in 2017 - 2019 and (2) characterize these UPA cases and their pregnancy outcome. UPA severity (Placental abnormality score (PSc) 1-3; low to high), nine treatment regimens (TM1-9) used in UPA cases and treatment duration as well as subsequent fertility were analyzed in the group of UPA mares. The proportion of pregnancies affected by UPA was 4.2% (n=177/4192). Placental abnormality severity was scored as PSc1 (51.4%), PSc2 (32.8%) and PSc3 (15.8%). The generalized mixed model revealed PSc was affected by mare age and mare status (own pregnancy (OP) or embryo transfer recipient (ER)) (P=0.035) with ER mares having increased PSc compared with mares having their own pregnancy. Abortion occurred in 17/177 (9.6 %) UPA pregnancies. Overall, at the end of the next season, 61.1% of UPA mares were pregnant, 32.0% barren, and 6.9% open (n=175). Pregnancy was established in 62/91(68.1%) of mares with PSc1, 31/58 (53.4%) with PSc2 and 14/26 (53.8%) with PSc3. Most pregnancies were achieved in the first 81/107 (75.7%) or second 18/107 (16.8%) inseminated cycle. In conclusion, early detection and treatment of ultrasonographic assessed placental abnormalities can save high-risk pregnancies in > 90% of cases with a satisfying subsequent fertility.