Direct determination of optimal amino acid intake for maintenance and growth in broilers

This study has used a direct approach to calculate the optimal dietary supply of amino acids for maintenance and growth in broiler chicks. Amino acid intake and accretion in the carcass in Ross 308 chicks was measured following the feeding of different experimental diets with controlled feed intake from hatching through 42 d. Increasing crude protein levels at constant amino acid:protein ratio improved growth and reducing the crude protein levels at constant amino acid:protein ratios depressed performance. Altering the protein at constant essential amino acid concentrations had little affect on growth. Plotting the amino acid intake per metabolic BW against amino acid accretion per unit of metabolic BW yielded a straight line whose slope represents the efficiency of utilization of the amino acid for growth; the intercept represents maintenance. These values were then used to calculate the amino acid intakes required for any BW and growth rate. For comparison, inputs were calculated for the growth targets recommended in the Ross manual and compared with the dietary recommendations. The measured results were similar to the overall empirical recommendations although values differed slightly, with threonine required at higher levels then recommended. Using the growth rates obtained in this trial, optimal amino acid supply was compared with the NRC (1994) recommendations. This indicated that optimal amino acid supply was higher then NRC (1994) recommendations for most amino acids. The calculation of optimal amino acid supply as a function of BW and growth will allow effective formulation of diets for maximal efficiency.