An eight year old Thoroughbred mare presented to Cornell’s Equine and Nemo Farm Animal Hospital ( ENFAH) for acute onset of mild colic, gas distended colon, and persistent fever. Evaluation on presentation revealed a fever (103.3F) and no other abnormalities on physical exam. The colon was mildly gas distended on rectal palpation. Fast abdominal ultrasound revealed increased peritoneal fluid. An abdominocentesis was performed revealing flocculent orange fluid with an elevated nucleated cell count with few phagocytized gram negative bacteria. Culture of the peritoneal fluid was submitted and grew ​Actinobacillus​ species. Broad spectrum antibiotics (procaine penicillin potassium and enrofloxacin) were started and the fever improved within twelve hours. The mare’s clinical signs continued to improve. Repeated abdominocentesis and peritoneal fluid analysis demonstrated signs of improvement in nucleated cell counts. She was discharged after five days of hospitalization.