Polydipsia and polyuria in a weanling colt caused by nephrogenic diabetes insipidus

Nephrogenic diabetes insipidus in the horse is a rarely reported failure of the renal tubules to respond appropriately to vasopressin (also known as antidiuretic hormone). The most striking clinical presenting sign of polyuria and polydipsia is not uncommon, however, being attributable to many possible differential causes. In this case, a diagnosis of nephrogenic diabetes insipidus was made in a thin, 102-kg, 5-month-old weanling Quarter Horse colt. This diagnosis was based on laboratory values derived during baseline observation, water deprivation, antidiuretic hormone supplementation, and a Hickey-Hare test. With moderate water and sodium restriction, proper nutrition, and appropriate anthelmintic therapy, the colt began to grow at a more normal rate, gaining 68 kg in 90 days or 0.76 kg/d (1.66 lb/d).