The effect of hexoestrol on calcium metabolism in the sheep.

I . The effect of hexoestrol on calcium metabolism of wether lambs has been studied 5 weeks after implantation of the oestrogen by the use o f 4 T a combined with a balance technique. 2. Treatment resulted in significant increases in gain in body-weight, efficiency of food utilization and retention of Ca. 3. The increased retention of Ca resulted from an increase in the efficiency of absorption of dietary Ca and from a decrease in thc rate of excretion of Ca into urine and faeces (faecal endogenous Ca). 4. The rate of accretion of Ca into bone was increased significantly by the treatment, but the rate of resorption of Ca from bone remained unchanged. The net result was an increase in skeletal retention of Ca. 5. The size of the slowly cxchangeable pool of bone Ca also increased significantly. 6. The results suggest that hexoestrol promotes increascd growth and Ca retention in ruminants by altering the metabolism of Ca to that of a younger more actively growing animal. This result would be consistent with an incrcascd rate of secretion of growth hormone, the possibility of which is discussed together with the relationship between oestrogen and milk fever.