Factors affecting intestinal starch digestion in ruminants: A review

The process of starch assimilation in the ruminant is complex and remains an avenue by which increases in production efficiency can be gained. Ruminal starch digestion is typically 0.75-0.80 of starch intake. Starch that escapes fermentation and flows to the small intestine may be more resistant to enzymatic digestion and on average 0.35-0.60 of starch entering the small intestine is degraded there. Of the fraction that escapes small intestinal digestion an additional 0.35-0.50 is degraded in the large intestine. This suggests that limitations to small intestinal starch digestion do exist. This review summarizes available information describing the digestive and absorptive processes occurring in the small intestine with an emphasis on nutritional factors that influence these processes. A review of experiments measuring small intestinal starch digestion indicates that small intestinal digestion is either highly variable or poorly determined whereas ruminal and large intestinal digestion are much more clearly described. These data indicate that improvements in methodologies are needed before we can accurately describe processes occurring in the small intestine and formulate diets to optimize site of starch digestion.