Comparison of methodologies to determine the apparent ileal amino acid digestibility of maize, wheat, lupins, and peas for broiler chickens

C.L Nalle,V Ravindran

doi:10.3920/jaan2021.0005

Abstract

The influence of method (direct vs difference method) used to determine the apparent ileal digestibility coefficient (AIDC) of amino acids in two cereals (maize and wheat) and two grain legumes (Australian sweet lupins and peas) was investigated. For the direct method, the test ingredients were incorporated as the sole source of protein in assay diets. The assay diets used in the difference method were formulated by substituting the cereals and legumes for 50 and 25% (w/w), respectively, of a maize-soy basal diet. Each diet contained 3 g/kg titanium dioxide as an indigestible marker and were offered ad libitum to four replicate cages of broilers (four birds/cage) from d 28 to d 35 post-hatching. On d 35, digesta were collected from the terminal ileum and the AIDC of amino acids were calculated using marker ratios in the diet and digesta. Except for histidine, methionine, cysteine and tyrosine, the main effect of methods was found to be significant (P<0.05 to 0.001) for the AIDC of all amino acids. The main effect of the ingredients was significant (P<0.05 to 0.001) for all amino acids, except for histidine, aspartic acid and serine. Interactions (P<0.05) between ingredients and method were observed only for leucine, lysine, proline and serine. The AIDC of amino acids, determined by the difference method, was found to be distinctly higher than those determined by the direct method. This suggested that the direct method underestimated amino acid digestibility in low and medium protein ingredients.

Highlights

Published data on the apparent ileal digestibility coefficient (AIDC) of amino acids from feed ingredients for poultry show large differences and even in samples within the same feedstuffs (Bryden et al, 2009)
The difference method has been used in limited number of studies such as Nalle et al (2011a,b), who reported the AIDC of amino acids in peas and sweet lupins
The application of the direct method measurement resulted in the underestimation of the AIDC of most amino acids in the ingredients tested

Summary

Introduction

Published data on the apparent ileal digestibility coefficient (AIDC) of amino acids from feed ingredients for poultry show large differences and even in samples within the same feedstuffs (Bryden et al, 2009). The direct method is most commonly used to measure amino acid digestibility in feed ingredients, largely because of the simplicity of the assay diet and calculations (Ravindran and Bryden, 1999). In this method, the test ingredient represents the sole source of amino acids in a dextrose or starch-based assay diet, fortified with minerals and vitamins. The digestibility calculations assume that the amino acid digestibility of the diet is representative of that of the feed ingredient This assumption is not always true and can lead to some errors in calculations because the diet itself triggers the secretion of endogenous amino acids. This error will be exacerbated as the amino acid concentration in the test diet decreases (Lemme et al, 2004)

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