Clinical Study of Nutritional Secondary Hyperparathyroidism in Horses

Abstract

SUMMARY Nutritional secondary hyperparathyroidism was diagnosed, studied, and treated in 7 horses from southern or eastern Texas or southwestern Louisiana during a period of approximately 1 year. The disease was characterized by bilaterally symmetrical, firm, pyramidal enlargement of the facial bones immediately above and anterior to the facial crests, by thickening of the horizontal rami of the mandible, and by transitory lameness of 1 or more limbs. One of the horses made satisfactory improvement while being fed alfalfa hay (calcium-phosphorus ratio of 6:1), another horse became more severely affected by the disease while being fed a balanced ration supplemented with disodium phosphate (calcium-phosphorus ratio of 1:10.5), and a 3rd horse improved slowly while being fed a balanced ration (calciumphosphorus ratio of 1.15:1). Lameness disappeared and all of the horses became physically sound after they were fed a high calcium ration for 4 to 6 weeks, but the enlarged bones of the skull did not regress in size in most of the horses. Low calcium and high phosphorus concentrations occurred in the urine of these horses. These laboratory tests were of greater diagnostic value than were the measurement of serum calcium and inorganic phosphorus concentrations and serum alkaline phosphatase activity.