EFFECT OF OESTROGEN ADMINISTERED IN EARLY OR LATE LACTATION ON THE YIELD AND COMPOSITION OF MILK IN SHEEP

Abstract

SUMMARY Subcutaneous injections of oestradiol benzoate (OB) were given daily to lactating ewes for 7 days beginning 20 (early lactation) or 46 (late lactation) days after parturition. Injections of 50 and 500 μg OB enhanced milk yield in ewes during late lactation and resulted in significant increases in the proportion and daily production of milk components. During early lactation, injections of 500 μg OB failed to enhance milk yield but significant increases in the fat content of milk were recorded. The administration of 5000 μg OB resulted in a marked decline in milk yield. In milk from these ewes there was a fall in lactose content with a concomitant rise in the number of leucocytes and proportion of vacuolated macrophages suggesting that mammary involution had begun.