Amino acid digestibility of whole yeast and autolysed yeast derived from sugarcane ethanol production and effects on excreta bacterial populations in caecectomised laying hens

Yeast biomass represents a renewable source of single-cell protein that can be used as an alternative feed ingredient in laying hen diets. The objective of this study was to determine the amino acid (AA) digestibility and excreta bacterial populations of whole yeast and autolysed yeast in caecectomised laying hens. Six caecectomised laying hens were housed individually in metabolism cages and fed either a basal diet or one of two diets, containing either whole yeast or autolysed yeast. The diets and hens were applied in a duplicate 3 × 3 Latin square design. In each period, the laying hens were fed their respective diet for 8 d and excreta samples were collected quantitatively twice daily during days 5–8. On day 9, a sterile plastic bag was attached to the cloaca of each hen to collect excreta for microbiota analysis. The crude protein (CP) contents were 342 and 334 g/kg dry matter (DM) in the whole yeast and autolysed yeast, respectively. The contents of neutral detergent fibre and acid detergent fibre were higher in the whole yeast (158 and 21 g/kg DM, respectively) than in the autolysed yeast (65 and 1 g/kg DM, respectively). Both in vitro protein digestibility and AA digestibility in the caecectomised laying hens were higher (p < 0.05) in the autolysed yeast than in the whole yeast. However, there were no differences (p > 0.05) in the gene copy numbers of bacteria among the experimental diets. This suggests that yeast products derived from sugarcane ethanol production could be considered alternative protein sources. Accurate information on the AA digestibility of yeast products is important for estimating their contribution to digestible AA supply and for their appropriate inclusion in laying hen diets.