1. The relationships between the intakes of protein and of non-protein energy (NPE), nitrogcn retention and body protein synthesis have been studied in female pigs weighmg 30 and 35 kg. 2. Four animals were assigned to three regimens and given a conventional (basal) diet supplemented with fat, carbohydrate or protein. After 1 week, measurements of N excretion in urine and faeces (7 d collection) and gaseous exchange (3-4 d) were made. At the end of the balance period a solution of

more »

... was infused at a constant rate. Body protein synthesis was then calculated as the difference between the apparent irreversible loss of blood leucine and the loss of "C in expired air. The animals were then offered the basal diet without supplement for 10 d and the measurements of N retention, energy retention and protein synthesis were repeated. 3. The intakes of metabolizable energy (ME; MJ/kg body-weight (W)0'76 per d) were 1.75 for fat, 1.58 for carbohydrate, 1-25 for protein and 1.18 for the basal diet; corresponding intakes of apparently digestible N (ADN; g N/kgWo'6 per d) were 2.30,2.31,4.35 and 2-17. Daily N retention, which during the period of basal feeding was 13.6 g was increased by between 3.4 and 7.2 g by the supplements. Daily fat deposition was also increased in the animals that received the diets supplemented with carbohydrate and fat.