Effects of undernutrition in late pregnancy on the nitrogen and energy metabolism of ewes

Abstract

The nitrogen metabolism of five non-pregnant ewes and 16 pregnant ewes was studied. The aim was to examine the effects of pregnancy on the response to severe undernutrition. Some measurements of energy metabolism and blood composition were also made. Pregnant ewes excreted less urea nitrogen in the urine than did non-pregnant ewes when they were all well fed. When food intake was reduced by 75%, excretion by the non-pregnant ewes declined, whereas excretion by the pregnant ewes declined less or increased. After 5 days on the lower ration, pregnant ewes excreted up to 9 g more urea nitrogen daily than did non-pregnant ewes. Urea clearance was constant throughout and was 30–40% of creatinine clearance. Undernutrition caused hypoglycaemia and hyperketonaemia in the pregnant ewes only but there were no clinical signs of pregnancy toxaemia. The heat production of pregnant ewes declined when their ration was reduced. The estimated heat increment of pregnancy was greater with the reduced ration than with the large ration and it is suggested that this change represented the energy cost of gluconeogenesis and ketogenesis from protein. The gross energy content of protein apparently oxidized was estimated to be about 20% of the energy requirement of the foetus. The effects of pregnancy on nitrogen and energy metabolism and on response to undernutrition were approximately proportional to the birth weight of the lamb, and were smaller 7 weeks before lambing than 2 weeks before lambing.