Glucose and Lactate Absorption and Metabolic Interrelationships in Lambs Switched from Low to High Concentrate Diets

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Abstract
Two experiments were conducted to measure glucose and lactate absorption and metabolic interrelationships in lambs either switched gradually (experiment 1) or abruptly (experiment 2) from hay to a high concentrate diet. In experiment 1, seven lambs were given primed, continuous, 3-hour infusions of 2-[3H]glucose, U-[14C]L-lactate and para-aminohippuric acid (portal blood flow indicator) before and after switching from a pelleted hay to a pelleted, 85% concentrate diet. Blood samples were collected at 20-minute intervals during infusions. In experiment 2, four lambs were abruptly switched from a pelleted hay to an all-concentrate diet. Portal and arterial blood samples were collected before and up to 1 week after the diet switch. As a result of increased concentrate intake (experiment 1) net portal absorption and turnover of L-lactate and glucose increased. Percentage of glucose derived from L-lactate decreased. Net portal D-lactate absorption, L-lactate absorption as a percentage of turnover and conversion of L-lactate to glucose were not affected by diet. Lambs in experiment 2 did not become acutely acidotic. The insult to acid-base status peaked 12–16 hours after the diet switch, concurrent with maximum arterio-venous differences in plasma L-lactate and glucose. Arterio venous differences in plasma D-lactate were not significantly affected.