Development of the indicator amino acid oxidation technique in chickens: calibration of oxidation system and determination of bicarbonate retention factor.

The indicator amino acid oxidation technique has been widely used as a rapid and sensitive method to determine amino acid requirement. In this technique, the indicator 14C-amino acid is continuously infused and breath 14CO2 is collected to determine oxidation rate, which is used to predict requirement. However, a portion of the 14CO2 produced from amino acid oxidation is retained in the body and must be determined to correct oxidation rates based on breath 14CO2 collection. To develop the indicator amino acid oxidation technique for use in poultry, it is important to accurately measure expired and retained CO2; these measurements were accomplished using intravenous infusion of NaH14CO3. Oxidation chambers were constructed and calibrated to ensure complete collection of breath 14CO2. Hydrochloric acid was infused over 1 h into a beaker containing NaH14CO3 in four closed oxidation chambers, and the 14CO2 released was collected over 2 h. Of the initial radioactivity dose, 99.3 +/- 1.9% was recovered in collected 14CO2. We concluded that the oxidation chamber apparatus is adequate for complete recovery of expired 14CO2. In Experiment 2, we determined bicarbonate retention in five broiler breeder roosters from a primed, constant infusion of NaH14CO3 into the jugular vein for 4 h. At steady state, 86.0 +/- 1.4% of NaH14CO3 infusion was recovered in breath. Because 14% of infused 14C is retained within the body, the present results demonstrate the need to determine bicarbonate retention in chickens during oxidation studies and use it as a correction factor in subsequent experiments.