Case report: Obstructive Urolithiasis in a Feedlot Steer

An outbreak of urolithiasis occurred in a small beef cattle feedlot feeding a total mixed ration containing cracked com, com gluten, gluten balancer, hay and di- atomaceous earth. A1100 lb (500 kg) steer was presented to the Iowa State University Veterinary Diagnostic Laboratory for euthanasia and necropsy. Clinical signs included frequent tenesmus, evidence of abdominal pain, regurgitation and labored breathing. Serum chemistry revealed elevated BUN (160 mg/dl), creatinine (28.9 mg/ dl), creatine kinase (2253IU/L), and an inverted calcium- to-phosphorus ratio of 0.8. At necropsy, complete obstruction of the urethra with calcium phosphate (apatite) calculi was present. Based on the clinical pathology and extensive tissue damage in this animal, the prognosis was poor if surgical treatment had been elected.Analysis of the total mixed ration revealed a calcium-to-phosphorus ratio of 1:1. This case highlights the importance of a prompt diagnosis of urinary calculi in symptomatic animals, and evaluation of the ration for possible mineral imbalances.