title: A mechanistic model of small intestinal starch digestion and glucose uptake in the cow.
abstract: The high contribution of postruminal starch digestion (up to 50%) to total-tract starch digestion on energy-dense, starch-rich diets demands that limitations to small intestinal starch digestion be identified. A mechanistic model of the small intestine was described and evaluated with regard to its ability to simulate observations from abomasal carbohydrate infusions in the dairy cow. The 7 state variables represent starch, oligosaccharide, glucose, and pancreatic amylase in the intestinal lumen, oligosaccharide and glucose in the unstirred water layer at the intestinal wall, and intracellular glucose of the enterocyte. Enzymatic hydrolysis of starch was modeled as a 2-stage process involving the activity of pancreatic amylase in the lumen and of oligosaccharidase at the brush border of the enterocyte confined within the unstirred water layer. The Na+-dependent glucose transport into the enterocyte was represented along with a facilitative glucose transporter 2 transport system on the basolateral membrane. The small intestine is subdivided into 3 main sections, representing the duodenum, jejunum, and ileum for parameterization. Further subsections are defined between which continual digesta flow is represented. The model predicted nonstructural carbohydrate disappearance in the small intestine for cattle unadapted to duodenal infusion with a coefficient of determination of 0.92 and a root mean square prediction error of 25.4%. Simulation of glucose disappearance for mature Holstein heifers adapted to various levels of duodenal glucose infusion yielded a coefficient of determination of 0.81 and a root mean square prediction error of 38.6%. Analysis of model behavior identified limitations to the efficiency of small intestinal starch digestion with high levels of duodenal starch flow. Limitations to individual processes, particularly starch digestion in the proximal section of the intestine, can create asynchrony between starch hydrolysis and glucose uptake capacity.
authors.affiliation: Centre for Nutrition Modelling, Department of Animal Biosciences, University of Guelph, Guelph, ON N1G 2W1, Canada.
authors.forename: J A N
authors.initials: JAN
authors.lastname: Mills
authors.affiliation: Centre for Nutrition Modelling, Department of Animal Biosciences, University of Guelph, Guelph, ON N1G 2W1, Canada. Electronic address: jfrance@uoguelph.ca.
authors.forename: J
authors.initials: J
authors.lastname: France
authors.affiliation: Centre for Nutrition Modelling, Department of Animal Biosciences, University of Guelph, Guelph, ON N1G 2W1, Canada; Animal Nutrition Group, Wageningen University & Research, 6708 WD, Wageningen, the Netherlands.
authors.forename: J L
authors.initials: JL
authors.lastname: Ellis
authors.affiliation: School of Agriculture, Policy & Development, University of Reading, Reading, RG6 6AR, United Kingdom.
authors.forename: L A
authors.initials: LA
authors.lastname: Crompton
authors.affiliation: Wageningen UR Livestock Research, 6708 WD, Wageningen, the Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Bannink
authors.affiliation: Department of Dairy Science, Virginia Tech, 3310 Litton Reaves, Blacksburg 24061.
authors.forename: M D
authors.initials: MD
authors.lastname: Hanigan
authors.affiliation: Animal Nutrition Group, Wageningen University & Research, 6708 WD, Wageningen, the Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Dijkstra
mesh_terms: D000018:Abomasum / Q000378:metabolism; D000681:Amylases / Q000378:metabolism; D000818:Animals; D002417:Cattle; D004063:Digestion; D020895:Enterocytes / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism*; D006868:Hydrolysis; D007421:Intestine, Small / Q000378:metabolism*; D009844:Oligosaccharides / Q000378:metabolism; D010179:Pancreas / Q000201:enzymology; D013213:Starch / Q000378:metabolism*
chemical_list: D009844:Oligosaccharides; D013213:Starch; D000681:Amylases; D005947:Glucose
keywords: glucose uptake; mechanistic model; small intestine; starch digestion