A nine-year-old Holstein dairy cow presented to Cornell University Equine and Farm Animal Hospital for acute onset anemia. On presentation, she was quiet, but alert and responsive. Her physical examination revealed pallor, tachycardia, and weakness. There was no evidence of acute blood loss on physical examination or with point of care diagnostic testing. The patient was stabilized with a transfusion of six liters of bovine whole blood and treated for a presumptive Anaplasma marginale infection. Blood smear evaluation performed by the Clinical Pathology service revealed racquet to oval shaped piroplasms consistent with either Theileria or Babesia species. A broad PCR amplified and identified Theileria, a reportable blood parasite endemic to Africa, the Mediterranean, and Asia. The patient failed to respond to supportive treatment, antimicrobial therapy with oxytetracycline and imidocarb, and euthanasia and necropsy were elected.