METABOLISM AND NUTRITION A Collaborative Study to Evaluate a Precision-Fed Rooster Assay for True Amino Acid Availability in Feed Ingredients

ABSTRACT A collaborative study involving six laboratories was undertaken by the US Animal Nutrition Research Council to evaluate a precision-fed rooster assay as a means of measuring biological availability of amino acids in a variety of feedstuffs for poultry. Despite differences in analytical and bioassay methodology, there was good agreement in true amino acid availability (TAAA) values between laboratories for the six different feed ingredients and two mixtures tested. However, considerable variation was reported in total amino acid values for identical and com-monly used feed ingredients. The excellent agreement that existed between the TAAA values found for the mixtures of ingredients with those calculated from the data found for the com-ponents suggests that TAAA values are additive. The TAAA values from two sources of meat meals, which had widely different true metabolizable energy values without and with the nitrogen correction (TME and TMEn), demonstrate that differences in energy values should not be in-terpreted as an indication of differences in protein quality, because the TAAA values of these meat meals were nearly identical. Data from three different laboratories indicated that cystine in meat meal was less available than other amino acids. Recommendations for improvement and applica-bility of the assay are suggested, as are areas for future research. (Key words: true amino acid availability, corn, soybean meal, meat meal, corn gluten meal, wheat middlings, ingredient mixtures, true metabolizable energy, nitrogen-corrected true metabolizable energy