Studies on the carbohydrate metabolism of sheep. XVII. Feed requirements and voluntary feed intake in late pregnancy, with particular reference to prevention of hypoglycaemia and hyperketonaemia.
The increase in nutrient requirements of ewes with advancing pregnancy has been measured in terms of the additional feed necessary to prevent hyperketonaemia, with particular reference to the difference between ewes carrying single and those carrying twin lambs. The additional feed required during late pregnancy to prevent the ewe drawing appreciably on body reserves depended on the total foetal weight. In twin-bearing ewes the increase in the last 2 weeks of pregnancy was as high as 80% of the ewe's own maintenance requirements; the total requirement usually exceeded the voluntary feed intake during this period. It is concluded that the efficiency of utilization of the metabolizable energy of the additional feed is low, and that the additional feed requirement depends on the bodily condition of the ewe. In contrast to ewes in medium body condition, the voluntary feed intake of fat, twin-bearing ewes declined markedly in late pregnancy. This decline was not simply a consequence of reduction in abdominal space due to the large volume occupied by twin foetuses or by abdominal fat. The fat pregnant ewe, when undernourished as a result of a marked decline in voluntary feed intake, was better able to maintain blood glucose, and hence blood ketone levels, in the normal range than the ewe in medium body condition, but there was evidence that birth weights and viability of twins were low. In consequence, the usefulness of ketone level as a general criterion of undernutrition during pregnancy is restricted, but it is suggested that the technique used has special applications in nutritional studies on pregnant ewes.