The Utilization of Plasma Free Amino Acid and Glucose Carbon by Sheep

By the use of a constant infusion isotope dilution method, the rate of utilization of plasma glucose and the plasma free amino acid fraction in 2 sheep on a diet of hay which provided 49 g. crude protein daily and in 2 sheep on a grass nut diet containing 88 g. crude protein per day have been measured. Under steady state conditions, the mean rate of free amino acid utilization by the sheep on the grass nut diet of 4·25 mg./min./kg. was higher than the mean rate of 2·6 mg./min./kg. for those on the hay diet. The mean total glucose utilization rate of 2·25 mg./min./kg. on the grass nut diet was higher than the rate of 1·2 mg./min./kg. on the hay diet. The mean rate of production of glucose from free amino acids was higher at 0·33 mg./min./kg. on the high protein diet than the mean rate of 0·15 mg./min./kg. on the low protein diet. The mean percentages of CO2 derived from amino acids were 33% on the hay diet and 42·75% on grass nuts. Both these figures were greater than the percentages of CO2 derived from glucose which were 12·8 and 21% respectively. Five per cent of amino acids on the hay diet and 6·7% on the grass diet were converted to glucose. On the hay diet 12·8% and on the grass diet 14·7% of glucose was derived from amino acids. Between 50 and 85% of glucose and 55 to 68% of free amino acids were oxidised directly to CO2 on both diets.