The effect of 1-α-hydroxycholecalciferol on calcium and phosphorus metabolism in the lactating ewe

Abstract

1. The effect of 1-α-hydroxycholecalciferol (1 α-OH-D₃) on calcium and phosphorus metabolism has been studied in ewes at peak lactation by a combination of a mineral balance and a radioisotope technique.2. The rate of Ca absorption was substantially higher in the treated ewes than in controls. The rates of endogenous loss of Ca into urine, faeces and milk, however, were only slightly higher.3. In consequence, the net retention of Ca was increased and the loss of skeletal reserves of Ca normally associated with peak lactation, prevented.4. Although the rate of bone accretion increased slightly, the increase in skeletal retention of Ca resulted mainly from a decrease in the rate of bone resorption.5. This finding conflicts with the generally held belief that bone resorption is increased by cholecalciferol treatment.6. The rates of apparent absorption and retention of P were increased by the treatment probably as a result of a direct effect of the 1α-OH-D₃on P absorption.7. These results provide a possible explanation of the beneficial effect of 1α-OH-D₃in preventing parturient paresis (milk fever) in the dairy cow.