Effect of Diet on Glucose Entry and Oxidation Rates in Ponies

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Abstract
Glucose entry and oxidation rates were studied in four Shetland ponies fed rations consisting primarily of oats or alfalfa-beet pulp, or fasted for 72 hours. Digestible energy (DE) intake was greater from the alfalfa diet (7200 kcal) than from the oat diet (6400 kcal); however, total glucose entry rates were 30% greater from the oat diet, suggesting a greater availability of glucose from the oat ration. Likewise, glucose contribution to oxidative metabolism was greater from the oat ration (15.8%) than from the alfalfa-beet pulp ration (9.2%). The glucose pool was unaffected by dietary treatment, but plasma glucose concentration was significantly lower in ponies fed the oat ration than when fed the alfalfa-beet pulp ration. Plasma insulin increased with glucose entry rate and was correlated with the nonoxidized rather than oxidized glucose. Glucose oxidation rates and percentage CO2 from glucose increased linearly with entry rates, demonstrating a preferential fuel for metabolizable energy as more glucose became available for absorption. However, in the fasted animal, glucose contribution to total CO2 production was only 8.8% which demonstrated an oxidative requirement similar to that of ruminants. Fasting glucose entry rates representing hepatic glucose output were 0.18 g/hour/kg0.75. Glucose metabolism in fasted ponies or ponies fed the alfalfa diet appeared to be more comparable to quantitative data in ruminants; however, the nonruminant pattern of metabolism was approached on the high grain ration.