Effect of exercise and of meals of differing starch content on glucose kinetics and muscle glycogen utilization and replenishment in horses.

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A combination of plasma and muscle biochemical methods, indirect calorimetry, isotopic tracer studies ([6,6-2H]glucose as constant rate infusion) and real-time reverse transcription polymerase chain reaction techniques were used to gain a better understanding of the effect of ingestion of meals of differing starch content prior to or after exercise by horses. In the first study (Chapter 3), horses were fed before exercise either (1) corn, (2) an isocaloric amount of alfalfa cubes (51.4 KJ/kg DE), or (3) not fed. The main finding was that meal type prior to exercise modestly altered substrate use during exercise such that corn feeding resulted in greater carbohydrate oxidation due to higher skeletal muscle utilization of blood-borne glucose, unchanged muscle glycogenolysis and lower whole body lipid oxidation. In the second study (Chapter 4), the glycemic response to ingestion of cereals (cracked corn, steamed oat groats or rolled barley) and intragastric administration of glucose was assessed by giving equal amounts of hydrolyzable carbohydrates. We determined that oat groats, corn and barley have similar areas under the plasma glucose concentration time curve in horses, and compared with the glycemic index of 100, these cereals were approximately 60. In the third study (Chapter 5), horses with exercise-induced muscle glycogen depletion were either not fed for 8 h, fed mixed alfalfa and grass hay (~15 Mcal, ~62 MJ DE), or fed an isocaloric amount of corn immediately and 4 h after exercise. The main findings were that corn feeding, when compared to feed withholding, resulted in mild to moderate hyperglycemia and hyperinsulinemia, and a 3-fold greater whole body availability and utilization of glucose. However, muscle glycogen replenishment was only minimally enhanced. In the last study (Chapter 6), we described the effect of glycogen-depleting exercise and of meal type after exercise (as in Chapter 5) on the insulin responsive glucose transporter (GLUT4) gene expression in skeletal muscle. We found that GLUT 4 gene expression in muscle increased by ~2-4 fold during 24 h after exercise, when compared to that prior to exercise but no differences were observed due to meal type fed after exercise.
Original languageEnglish
TypePhD thesis
Publication statusPublished - 2004


  • carbohydrate oxidation
  • glucose
  • glycogen
  • grains
  • horses
  • lipid oxidation
  • muscle
  • roughage


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