Vitamin D‐dependent rickets in a Saint Bernard dog

Rickets diagnosed in a 12‐week‐old female St Bernard was attributed to an inborn error in vitamin D metabolism. Radiographically the physes were enlarged radially and axially, and metaphyseal bone adjacent to the physes was widened and cup‐shaped. Serum biochemical abnormalities were hypocalcaemia, hypomagnesaemia, and hyperparathyroidism. Treatment was given with dihydrotachysterol, a synthetic sterol that is metabolised to a pharmacologically active analogue of 1,25 dihydroxycholecalciferol by the liver. This resolved the rachitic skeletal lesions completely in six weeks, as assessed radiographically, and maintained the serum calcium at the lower end of the normal range.