Right dorsal colitis in horses has been associated with administration of phenylbutazone. Although reports of right dorsal colitis in this species have described surgical treatment associated with a poor prognosis, we have had success treating this condition medically. This report describes 5 horses with right dorsal colitis confirmed during celiotomy that were initially managed medically. All horses had a history of intermittent abdominal pain; weight loss was noted in only 1 horse. The doses (2.0 to 4.6 mg/kg PO bid) and duration (5 to 30 days) of administration of phenylbutazone were not unusually high relative to those recommended (4.4 mg/kg PO bid). Hypoproteinemia and hypoalbuminemia were observed in all horses at the time of admission; packed cell volume was low in 4 horses, and hypocalcemia was also observed in 4 horses. Three ight dorsal colitis has been experimentally and clini-R cally associated with administration of phenylbutazone to horses.'" Clinical signs associated with right dorsal colitis include anorexia? weight loss, intermittent or sporadic episodes of acute abdominal pain, and diarrhea.'-3 Surgical treatment is advocated in prior reports; however, the prognosis for affected horses is poor.'" At the Texas Veterinary Medical Center (TVMC), some horses with right dorsal colitis identified during celiotomy have been managed medically. The purpose of this retrospective study is to review the signalment, history, physical examination, clinicopathologic findings, and response of treatment in horses with right dorsal colitis managed medically. Materials and MethodsAll horses with right dorsal colitis managed medically at the TVMC between January I , 1985, and December 31, 1993, were included in the study. Five horses were identified by reviewing the medical records. All horses were used for athletic performance. The diagnosis of right dorsal colitis was made on the basis of surgical findings in 4 horses and at necropsy in 1 horse. Diagnosis of right dorsal colitis was based on gross findings of marked edema, thickening, or reduction in diameter of the intestinal tract restricted to the right dorsal colon. In each case, other gross intestinal lesions were absent, and the cause of abdominal pain was attributed to abnormalities of the right dorsal colon. Horses that had right dorsal colitis, but that were not managed medically, and horses that had other visible intestinal abnormalities accompanying right dorsal colitis were excluded from the study.The medical record of each horse was reviewed to abstract the following information: ( I ) date of admission; (2) gender; ( 5 ) character and duration of clinical signs prior to admission; (6) history and duration of treatment with nonsteroidal antiinflammatory drugs (NSAIDs); (7) history of training and performance; (8) hematologic and serum biochemical data obtained at the time of admission; (9) results of cytological and biochemical analysis of peritoneal fluid obtained at the time of admission; (10) results of microbiologic culture of feces during hosp...