Parathyroid action on calcium, phosphorus, magnesium, and citric acid in dairy cattle

¹ University of Tennessee-Atomic Energy Commission Agricultural Research Laboratory, Oak Ridge, Tennessee; and Dairy Department, University of Georgia, Athens, Georgia

Parathyroidectomized lactating Jersey cows were used to study the effects of parathyroid extract (PTE) on calcium, phosphorus, magnesium, and citric acid metabolism. Treatments consisted of 0, 2,200, and 4,400 U.S.P. units of PTE per 1,000 lb of body weight per day for three experimental periods. Calcium 45 and phosphorus 32 were administered orally 56 hr after initiation of PTE treatment. The plasma calcium, but not C⁴⁵, showed an increase (P < 0.01) with parathyroid hormone treatment. Calcium and Ca⁴⁵ urinary excretion increased. In milk and plasma, high concentration of P³², but not of phosphorus, was associated with hormone administration. Total phosphorus and P³² in urine was increased with higher levels of PTE due to diuresis and greater concentration. Plasma levels of magnesium were not affected by PTE administration whereas an increase of magnesium concentration in milk occurred. A concomitant decrease was observed in the urinary excretion of magnesium. With increased PTE, citric acid levels of plasma and urine increased but remained constant in milk.