A 286-day pregnant mare was referred for signs of impending abortion. The ultrasonographic evaluation revealed a slightly increased combined thickness of the utero-placental unit (CTUP), oligohydroallantois and a living fetus. No vulvar discharge was observed, and the cervical swab culture was negative. After a choke, the mare received NSAIDs and antibiotics and then developed systemic inflammatory response syndrome (SIRS) and aborted. The amniotic portion of the umbilical cord was excessively long and twisted and the chorionic side of the placenta showed a brown discoloration and rough surface area. E. coli was isolated from all the fetal membranes, fetal fluids and tissues. Histologically, degeneration and necrosis with dystrophic calcification of the chorial villi at the cervical pole was found. The final diagnosis was abortion due to placental infarction with secondary placentitis. Cervical pole necrosis is a poorly understood condition of the allantochorion, and a histological exam is necessary to obtain a definitive diagnosis.