Abstract
Preceding to a series of experiment to determine the amino acid requirement of broilers, the effect of quality and quantity of dietary protein sources on the performance and concentration of plasma amino acid was studied. To the basal diet mainly consisted of corn, fish meal, soybean meal or whole egg protein was added as a main protein source to contain 0 and 25%, 5 and 40%, or 5 and 20% of diet. The two diets containing same protein sources were mixed to obtain diets containing 6 levels of crude protein (CP) arithmetically. Four-day old male broiler chicks were fed ad libitum experimental diets and water. On the 10th day, the body weights and feed consumptions were recorded and blood samples were taken to determine the plasma amino acid concentration. The maximum body weight gains were obtained at 16.5, 21.9 and 14.5% in dietary CP levels, and the minimum feed conversion ratios were obtained at 16.5, 18.8 and 15.5% in dietary CP levels for fish meal, soybean meal and whole egg protein, respectively. Several amino acid contents of diets which achieved the maximum body weight gains and the minimum feed conversion ratios were calculated to be lower than the NRC requirements in all diets, e.g. arginine, lysine, sulfur containing amino acid and tryptophan in fish meal diet, sulfur containing amino acid in soybean meal diet and arginine, lysine, sulfur containing amino acid, threonine and tryptophan in whole egg protein diet. The response pattern of plasma amino acid concentrations to the dietary CP levels were classified into three types. The concentrations of histidine and phenylalanine were not affected by kind and levels of protein sources. The concentrations of other amino acids remained low and then increased linearly with increasing the corresponding dietary amino acids. The concentrations of alanine, aspartic acid, glycine and glutamic acid reached plateaus at high protein levels. It was left as a subject to be discussed in future whether a break point of each amino acid agrees with the real requirement of amino acid.
