Studies on the carbohydrate metabolism of sheep. XVIII. The metabolism of glucose, free fatty acids, ketones, and amino acids in late pregnancy and lactation

Abstract

The metabolism of glucose, free fatty acids (FFA), ketone bodies, and amino acids in late pregnancy and lactation was studied at three levels of feeding in an experiment designed to measure the increase in nutrient requirements of ewes with advancing pregnancy.The plasma FFA level is a more sensitive criterion of undernutrition during pregnancy than the level of blood glucose or ketones. In ewes on a constant feed intake and in medium body condition approaching late pregnancy, the rate of mobilization of fat reserves necessary to maintain caloric homeostasis, as indicated by plasma FFA level, was closely correlated with total foetal weight in late pregnancy and with the level of milk production in the first month of lactation. However, these ewes were unable to maintain blood glucose levels in the normal range in late pregnancy; severe hypoglycaemia was present in twin-bearing ewes. Caloric homeostasis was best maintained in fat ewes fed ad libitum; variation in blood glucose and FFA levels during late pregnancy and early lactation was minimal, in spite of a marked and variable decline in feed intake in twin-bearing ewes in late pregnancy. Reduction of foetal demand for nutrients may prevent or defer the breakdown of homeostatic meohanisms, but appears to play a minor role in the maintenance of caloric homeostasis in the undernourished pregnant ewe. However, reduction in the level of milk production is a major factor in the undernourished lactating ewe; severe hypoglycaemia and hyperketonaemia are thus prevented. The metabolic effects of high foetal requirements of amino acids are discussed in relation to observed variations in plasma amino acid Level in late pregnancy.