Equine α-amylase: does it limit starch digestion in the small intestine of the horse?

Abstract

The amylolytic enzyme α-amylase is essential for the digestion of starch in the small intestine of the horse. While it had been previously documented that the concentration of this amylolytic enzyme in the equine small intestine is low, the ability of equine α-amylase to degrade cereal grain starch is poorly understood. In an experiment designed to compare the 'in vitro' starch digesting capacity (activity) of equine α-amylase with that of bacterial a-amylase it was observed that the equine α-amylase digested an average of 20% less starch during the 'in vitro' incubations. This result suggests that the apparently limited capacity of equine α-amylase to digest starch along with the low concentrations of α-amylase reported to be present in the equine small intestine may limit pre-caecal starch digestion. A second experiment investigated if the addition of exogenous glycanase enzymes to cereal grain diets fed to horses would improve small intestinal starch digestion. The results showed that the addition of α-amylase and amyloglucosidase (AMG) to a digestible starch source significantly elevated postprandial glycaemic responses suggesting an improvement in precaecal starch digestion . Thus it appears that the concentration and activity of equine α-amylase may be limiting small intestinal starch digestion in the horse.