Renal tubular acidosis in a mule mare

Summary Renal tubular acidosis (RTA) in horses is differentiated into type I (distal) and type II (proximal) forms. We report the diagnostic evaluation and treatment of type I RTA in a 13‐year‐old mule mare that was referred because of lethargy and inappetence of several weeks' duration as well as lack of manure, anorexia and mild colic for 3 days. In addition to mild impaction of the pelvic flexure of the large colon, clinical pathological examination confirmed severe hyperchloraemic metabolic acidosis and hypokalaemia. Based on an ammonium chloride load test, the mule mare proved unable to acidify urine. No cause of RTA could be determined. Treatment consisted of intravenous fluid therapy to stabilise acid–base and electrolyte status, followed by oral supplementation with sodium bicarbonate and potassium chloride. The mule mare was discharged after 1 week of hospitalisation with the recommendation to continue oral supplementation and monitor laboratory values regularly. Ten months after diagnosis, the owner reported the mare to be clinically healthy. Apart from a slightly elevated bicarbonate concentration, blood acid–base status and electrolytes had been within normal limits. Supplementation of sodium bicarbonate powder had been reduced but that of potassium chloride powder remained unchanged. To the authors' knowledge, this is the first report of type I RTA in a mule.