A comparison of total and digestible amino acids in diets for broilers and layers

Eleven samples of food ingredients were analysed for their total and true digestible amino acid content, apparent metabolisable energy and other components. Large batches of these ingredients were retained for a broiler and a layer experiment. Four layer diets were formulated at 0.97 and 0.90 of total and digestible amino acid requirements for egg production using the analysed ingredients. Eight broiler diets were also formulated from 1.0 to 0.91 of total and digestible amino acid requirements in starter and finisher diets. Proximate and amino acid analyses and AME values were within the normal range for the 11 foodstuffs. Digestibility of amino acids was high with very few exceptions, e.g. cottonseed meal, meat and bone meal. Diets formulated on a total or digestible amino acid basis gave no differences in egg production parameters or broiler production parameters with no effect of level of inclusion. However, the main effects showed that diets formulated on a total compared to a digestible amino acid basis gave better growth rate and feed conversion efficiency in broilers. It was concluded that nutrient specifications for layers and broilers are not sufficiently precise to be able to differentiate between 1.97 and 0.90 of requirement for egg production or 1.0 and 0.91 for broiler growth. The use of digestible amino acids may be justified in diet formulations only when unusual protein concentrates with low amino acid digestibility values are used in large amounts.