Development of procedures for determining the amino acid requirements of chickens by the indicator amino acid oxidation method

To better understand the amino acid requirements of chickens, a method is n eeded to determine a point estimate of the requirement. A method developed to determine the amino acid requirements of piglets and human infants by us ing the oxidation rate of an indicator amino acid as the test parameter was adapted for use in growing chickens. Polycarbonate chambers measuring 30 x 40 x 30 (L x W x H) were constructed to house one small mature chicken or several small immature chickens and to trap exhaled CO2. In the first exper iment, 10-d-old chicks (250 to 300 g each) were feed deprived for 12 h and given 1 g of a methionine-deficient diet (gavage) with L-[1-C-14]phenylalan ine. Peak oxidation of L-[1-C-14]phenylalanine occurred between 30 and 90 m in (-200 dpm/g). A linear rate of oxidation (slope = -1.84; r(2) = 0.96) wa s achieved by 120 min after feeding until after 180 min, when oxidation sta bilized at a low rate. The second experiment tested different chambers and chicks with the same treatment to show repeatability. There were four chick s (250 to 300 g each) in each of three apparently identical chambers. Chick s were given two meals labeled with L-[1-C-14]phenylalanine, 2 h apart. The CV for the 0- and 30-min collections were 17 and 10%, respectively. The CV for the remaining collections remained at <4%. These data supported a syst em of two feedings, 2 h apart to reduce variability and a collection period that included up to 3 h after the second feeding.