Effect of protein and energy in the diet of the early-weaned calf on the concentration of free amino acids in the blood plasma

Abstract

Three experiments were conducted with 108 male Friesian calves to determine the effect of protein and energy in the diet on the concentration of free amino acids in the plasma. In experiments 1 and 2, the diets contained 12 to 21 per cent crude protein, with urea or meat meal as the protein supplement. The diets were fed with and without sulphur supplementation. In experiment 3, the metabolizable energy content of the diets was changed from 2.2 to 1.8 Mcal kg-1 by the addition of 20 to 60 per cent roughage from lucerne meal or ground straw to the diets. Blood samples were collected from all calves at 11 weeks of age, and the concentration of free amino acids in the plasma was measured. As the protein content of the diets increased, the percentage of essential amino acids of the total amino acids in the plasma increased. The percentage of essential amino acids was also greater in the calves fed meat meal than in those fed urea. These changes were mainly due to increased concentrations of the branched chain amino acids and decreased concentrations of glycine and glutamic acid. The supplementation of the diets containing urea with sodium sulphate increased the concentrations of cystine and methionine in the plasma. As the metabolizable energy intake of the calves increased there was an increase in the concentration of total amino acids in the plasma. Hence, the effect of protein and energy in the diet must be considered in studying the concentration of amino acids in the plasma.