Starch utilisation in chicken-meat production: the foremost influential factors

Abstract

Starch is the chief dietary energy source for chicken-meat production, the majority of which is derived from the grain basis of diets for broiler chickens. The utilisation of starch from maize is of a high order in terms of ileal starch digestibility coefficients but this is not necessarily the case with wheat or sorghum. This may stem from the fact that maize essentially lacks the soluble non-starch polysaccharides in wheat and ‘non-tannin’ phenolic compounds found in sorghum. Numerous factors may influence starch digestibility with emphasis placed on starch–protein interactions as starch granules are located in the prolamin protein matrixes of grain endosperm. This close proximity facilitates any physical and chemical interactions and in this connection particular attention has been paid to kafirin, the dominant protein fraction in sorghum. Nevertheless, despite their apparent importance, the precise nature of starch–protein interactions has not been well defined. Exogenous phytases are routinely included in broiler diets primarily to liberate phytate-bound phosphorus; however, phytate may impede starch digestion and may retard glucose absorption. Additional feed additives, including non-starch polysaccharide-degrading enzymes, other exogenous enzymes and reducing agents may have the capacity to influence starch utilisation. Nevertheless, ileal and total tract starch digestibility coefficients are static parameters and overlook the digestive dynamics of starch, which is inappropriate given the possibility that slowly digestible starch enhances energy utilisation and feed conversion efficiency. However, if the slowly digestible starch concept is valid, the underlying mechanisms have not been fully elucidated. Consideration is given to the suggestion that slowly digestible starch ameliorates the catabolism of amino acids to provide energy to the gut mucosa by increasing the provision of glucose to posterior small intestinal segments. There is the prospect that whole grain feeding provides slowly digestible starch in addition to generating heavier relative gizzard weights. The digestive dynamics of starch and protein are inter-related and the digestion of starch and absorption of glucose should not be considered in isolation from protein digestion and amino acid absorption in the quest to improve the performance of broiler chickens. The foremost factor influencing starch utilisation in chicken-meat production may be the interaction between starch and protein digestive dynamics.