Morphology of starch digestion in the horse

Structure of starch in feed and chyme of horses (7 with a cannula at the caudal end of the jejunum and 2 with a cecal fistula) after feeding high starch diets (maize: whole, broken, ground, expanded and as silage, oats: whole, rolled or ground, rolled barley, raw potatoes, and tapioca) was investigated by light and electron microscopy. Structure of feed starch and morphology or starch degradation in the chyme corresponded to data on preileal starch digestibility which was investigated in a parallel study. Barriers for starch digestion in the gastrointestinal tract of the horse were structure of the plant storage organ, as for example, a tight connection between starch granules in maize gains as well as the structure of the starch granules itself. The highly digestible oat starch was degraded by exocorrosion around the grains, whereas in other, less digestible, starch types degradation occurred by endocorrosion via pin holes. The number and size of the pin holes increased with increasing preileal starch digestibility. The effect of various ways of decomposition on preileal digestibility increased with advanced destruction of the original starch structure. Expanding was most effective. The granules were destroyed completely and the starch became soluble. Simple examination by light microscopy is a fast method to evaluate the degree of starch decomposition in the feed.