Progress in comprehending the phytate-phytase axis in chicken-meat production

Abstract

After an extended delay, the level of acceptance of exogenous phytases by the global chicken-meat industry is now almost complete. Contemporary bacterial phytases degrade phytate primarily in the gizzard. The extent of phytate degradation determines the extent to which phytate-bound phosphorus (P) is liberated; however, studies designed to investigate phytate degradation along the digestive tract have generated some confusing outcomes. This may be related to the reactivity of the phytate moiety, coupled with problems with inert dietary markers and perhaps a lack of complete and uniform extractions of phytate from digesta due to variations in digesta pH and phytate solubility. Quite recently, phytase was shown to have profound impacts on sodium (Na) digestibility coefficients in four segments of the small intestine. This has obvious implications for intestinal uptakes of glucose and amino acids via their respective Na⁺-dependent transport systems and it is possible that phytate and phytase have reciprocal impacts on ‘sodium pump’ (Na⁺, K⁺-ATPase) activity. It has been recently demonstrated unequivocally that phytase has the capacity to increase amino acid digestibility coefficients to the extent that phytase may generate a ‘proximal shift’ in the sites of amino acid absorption. The impact of phytase on starch digestibility is more equivocal and phytase responses may stem more from enhanced glucose absorption rather than starch digestion. The acceptance of phytase is hardly surprising, given its capacity to increase P utilisation coupled with numerous other positive influences that are still being properly realised.