Abstract
Increased efficiency of nutrient utilization can potentially be gained with increased starch digestion in the small intestine in ruminants. However, ruminants have quantitative limits in the extent of starch disappearance in the small intestine. The objective is to explore the nutritional and physiological constraints that contribute to limitations of carbohydrate assimilation in the ruminant small intestine. Altered digesta composition and passage rate in the small intestine, insufficient pancreatic α-amylase and/or small intestinal carbohydrase activity, and reduced glucose absorption could all be potentially limiting factors of intestinal starch assimilation. The absence of intestinal sucrase activity in ruminants may be related to quantitative limits in small intestinal starch hydrolysis. Multiple sequence alignment of the sucrase-isomaltase complex gives insight into potential molecular mechanisms that may be associated with the absence of intestinal sucrase activity, reduced capacity for intestinal starch digestion, and limitations in the efficiency of feed utilization in cattle and sheep. Future research efforts in these areas will aid in our understanding of small intestinal starch digestion and glucose absorption to optimize feeding strategies for increased meat and milk production efficiency.
Highlights
Ruminants consume various types of carbohydrates at different stages of their production life cycle
Microbial-N and nucleosides, and biohydrogenated lipids flowing to the small intestine may alter responses of the pancreas and intestine to luminal nutrient flows
Ruminant carbohydrase activities of the pancreas and small intestine appear to respond differently to diet and luminal nutrient supply compared with nonruminants
Summary
Ruminants consume various types of carbohydrates at different stages of their production life cycle. The objective of this review is to explore the nutritional and physiological constraints that contribute to limitations of carbohydrate assimilation in the ruminant small intestine This includes digesta composition and passage rate, the extent of small intestinal disappearance, regulation of digestive enzymes and absence of sucrase activity, and possible limitations in glucose absorption. Obvious factors such as dietary intake, diet composition, foregut retention time, and foregut anatomy and digestive function differentiate the ruminant from nonruminants These factors contribute to the differences in digesta flow to the small intestine, which in turn, could affect how small intestinal function is coordinated. Differences in duodenal carbohydrate, nitrogen, and lipid composition between ruminants and nonruminants could potentially contribute to changes in digestive and absorptive functions in the small intestine because regulation of digestion and absorption can be coordinated through luminal nutrient flows [28]
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