Placentitis occurrence, 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 including placentitis. Common placentitis treatments combine antibiotics, non-steroidal anti-inflammatory drugs and progestins. However, clinical studies on spontaneous placentitis cases and treatments are missing. Therefore, the aim of this retrospective field study was to describe the occurrence and severity of placentitis, the abortion rate after placentitis diagnosis (based on udder development, combined-thickness-of-uterus-and-placenta and fetal fluid echogenicity) and treatment during pregnancy (2017-2019) on one warmblood stud farm. Furthermore gestational, placental and foal characteristics were analyzed to determine their association with the severity of placentitis, which was scored (Placentitis score (PSc) 1-3; low to high). Pregnancy day of diagnosis (PDD), placentitis treatment and subsequent fertility were recorded as well as the effects of mare's age and status (own pregnancy (OP) or embryo transfer recipient (ER)). Statistical analyses were conducted to analyze potential associations and significant effects on PSc using a Chi-Square test and a generalized linear mixed model. The proportion of pregnancies affected by placentitis was 4.2% (n=177/4192) occurring in 164 mares (3-24 years; Mean±SD= 11.8±5.10). After clinical diagnosis (PDD 256.7±50.4 days) mares were treated with one of nine different treatments (TM 1-9). Abortion occurred in 17/177 (9.6 %) pregnancies diagnosed with placentitis. The remainingplacentitis pregnancies were further characterized by decreased gestational length (330.1±10.04 days), foal birth weight (54.3±7.09 kg), foal height (103.6±4.28 cm) and placental weight (6.3±1.9 kg). Placentitis severity was scored as PSc1 (51.4%), PSc2 (32.8%) and PSc3 (15.8%). PSc was affected by mare's status (P=0.034) with ER mares having increased PSc compared with mares having their own pregnancy. PSc significantly influenced the choice of TM (χ² (16) = 161.4, P