CONDITIONS AFFECTING PLASMA AMINO-ACID PATTERNS IN CHICKENS FED PRACTICAL AND PURIFIED DIETS

After 1 h of fasting, total plasma amino acid concentration in the chick decreased to approximately half of the full-fed value. Within 3-6 h, most amino acids had returned toward the full-fed level but did not exceed it throughout a 48 h period of starvation. After 48 h fasting lysine, threonine and isoleucine accumulated 3-fold, 2-fold and 2-fold of the full-fed level, respectively. Serine and glutamic acid exceeded the full-fed level at 3 h and then declined. Alanine reached its highest level after 6 h of fasting and then declined. In full-fed chicks diurnal variations of plasma free amino acid concentrations were observed. The lowest and highest concentrations were observed at 11 a.m. and 8-11 p.m., respectively, under a 24 h lighting. Reference plasma amino acid patterns are reported for chicks fed a practical diet ab lib. In day old chicks, concentrations of total amino acids, methionine plus 1/2 cystine, lysine and arginine were high. Alanine and glutamic acid concentrations were low. Most amino acid concentrations declined gradually during the 1st 4 wk of life, but methionine plus 1/2 cystine, phenylalanine, threonine and serine concentrations decreased sharply between 2-4 wk. Lysine concentration continued to decrease in chicks fed the starter diet. At 20 wk, plasma amino acid concentrations had decreased considerably except for methionine plus 1/2 cystine and basic amino acids. The plasma amino acid pattern for chicks fed an isolated soybean protein diet was similar to that of chicks fed the practical diet.