Ileal Amino Acid Digestibility Assay for the Growing Meat Chicken - Assessment of a New Ileal Amino Acid Digestibility Assay for Broiler Chickens

The aim of the study was to evaluate the accuracy of ileal amino acid digestibility coefficients in dietary formulation for broiler chickens. Two relatively poor quality protein sources, a meat-and-bone meal and a dried blood meal were used. The meals were subjected to the ileal assay and respective mean coefficients of digestibility of 0.58 and 0.67 were found for the first-limiting amino acid methionine+cysteine. Subsequently, each of the meals was the sole source of protein in semi-synthetic maize starch based diets. A casein containing semi-synthetic maize starch based control diet was also formulated. The two test diets and the casein diet contained equal amounts of methionine+cysteine, which was clearly first-limiting. Methionine+cysteine was supplied at 60% of the NRC requirement for the growing bird. Two further semisynthetic maize starch-based diets were formulated, which contained either the meat-and-bone meal or the blood meal as the main sources of protein, but synthetic methionine was added so that the digestible methionine+cysteine content equaled that in the casein-based control diet. All amino acids other than methionine+cysteine were supplied in moderate excess of the requirements of the growing bird. The experimental diets were fed to broiler chickens in a conventional growth trial. Daily feed intakes were adjusted to achieve comparable feed and metabolizable energy intakes across all the diets. The significantly lower growth performance for birds on the unsupplemented meat-and-bone meal and blood meal diets indicated that the actual digestible methionine+cysteine level was lower in those diets compared to the control. That supplementation with synthetic methionine to give equal amounts of dietary ileal digestible methionine+cysteine restored parity in growth performance is evidence for the accuracy of the new ileal digestibility assay.