Variability in amino acid digestibility of wheat grains from diverse genotypes examined in caecectomised laying hens

Abstract

Summary The consideration of amino acid (AA) digestibility during feed formulation for laying hens is a useful approach that could increase the efficiency of protein utilisation. However, for practical applications, thorough information about the level and variation of AA digestibility, both between and within utilized feed components, is necessary. Approaches to rapidly predict AA digestibility under practical conditions are also needed. Wheat grains are typically used at high levels in the diets of laying hens, so they are an important AA source. Nevertheless, systematic studies investigating the AA digestibility of wheat grain in hens are scarce. Therefore, the objective of the present study was to determine the AA digestibility of 20 wheat genotypes, and to examine relationships between AA digestibility and the physical and chemical characteristics of the grains. Wheat genotypes were grown under standardised conditions within the collaborative research project GrainUp, and were comprehensively analysed based on their physical and chemical characteristics. Additionally, the in vitro solubility of nitrogen found in the wheat grains was determined. The 20 wheat genotypes were added to a basal diet at the expense of maize starch at 500Â g/kg to produce 20 wheat diets. The experimental design comprised four Latin Squares (6 × 6), which were equally distributed over two runs (resulting in 12 experimental periods). Caecectomised laying hens (LSL-Classic) were individually housed in metabolism cages, and were fed the respective experimental diets for eight days per period. During the last four days per period, excreta were collected quantitatively, and feed intake was recorded. Amino acid digestibility of the added wheat genotypes was calculated using a linear regression approach. The digestibility of all examined AA varied significantly between wheat genotypes, but digestibility was high overall. The largest differences between the extreme genotypes were observed in Met and Lys with 23 and 18 percentage points, respectively. Chemical and physical characteristics as well as the in vitro solubility of nitrogen significantly correlated with AA digestibility only in a few cases. Multiple linear regression analyses were used to predict AA digestibility based on the grain characteristics. The explanatory power of the equations (adjusted R²) was below 0.7 for most AA across the variable pools, so precision of the method does not warrant its use during feed formulation. Several explanatory approaches for the missing relationships are presented and discussed.