Facts and Thoughts on Carbohydrase Supplementation Effects on Amino Acid Digestibility in Broiler Chickens

Carbohydrases are widely used as feed additives in poultry. Traditionally, enzyme products were specific with lead activity of one or two enzymes, typically xylanases and β-glucanase. Main area of application were diets based on wheat, rye, and barley. More recent research considered multiple-carbohydrase mixtures, often combined with enzymes other than carbohydrases, and also targeted maize-based diets. Carbohydrase supplements can affect digestibility of nutrients other than carbohydrates, including amino acids. Published literature overall indicates a small increase in precaecal digestibility of amino acids in broilers when carbohydrases are supplemented. However, effects were not consistent among studies and highly variable. One possible reason is the variation that exists in composition and digestibility among batches of feed raw materials. In diets rich in non-starch non-cellulosic polysaccharides, the effect on amino acid digestibility is primarily related to the reduction of digesta viscosity achieved by enzyme supplementation. Causal relationships in maize-based diets are not well understood and the mode of action is difficult to study with multi-enzyme products. Partial depolymerisation of structural carbohydrates and better access to entrapped proteins may be one reason. Viscosity-related effects also change the composition of the intestinal microbiota. High digesta viscosity can stimulate the growth of pathogens. However, specific carbohydrate polymers originating from partial hydrolysis of complex structures have potential to support the growth of bacteria with positive effects on intestinal fermentation and overall bird development. It is unknown to date whether effects on the intestinal microbiota are related to amino acid digestibility.

Presented at the International Fibre Summit 2019 (https://internationalfibre.com/). Reproduced with permission from the organizers.