To determine the effect of diet and level of energy intake on glucose metabolism in sheep, four dietary treatments consisting of feeding a low-roughage (LR) and a high-roughage (HR) diet at each of two intake levels estimated to provide 586 and 1172 kJ (140 and 280 kcal) digestible energy (DE)/kg body-weight-0.75 per d were given to each of eight yearling rams in four different time periods each of 4 weeks duration. Both diets contained 140 g crude protein/kg using ground maize, mixed hay and soya-bean meal and were given in two meals/d. Estimated DE values of food were verified during the study and actual intakes of DE were within 9.5% of the estimated values. 2. To study glucose metabolism, a single intravenous injection of ]2-3H]glucose and subsequent withdrawal of nine venous blood samples with 3 h were made in each experiment. Two experiments were conducted on consecutive days for each sheep on each dietary treatment. 3. Coefficients of determination (r2) for linear regressions to measure the effect of time after a single injection of [2-3H)glucose on log specific radioactivity of plasma glucose were calculated for fifty-eight experiments. In fifty-six of the experiments, r2 values exceeding 0-95 were obtained. 4. Compared to the HR diet, the LR diet increased (P smaller than 0-05) the pool size and decreased (P smaller than 0-05) the half-life of glucose. At both intake levels, the LR diet increased (P smaller than 0-05) the plasma concentration and the entry rate of glucose compound to the HR diet but interaction (P smaller than 0-05) between diet and intake level was attributed to a greater difference obtained between diets at the higher compared to the lower level of food intake. Increasing the level of intake caused a greater (P smaller than 0-05) pool size and space, and a shorter (P smaller than 0-05) half-life of glucose. 5. It was concluded that substitution of roughage by concentrate in a ruminant's diet may increase the rate of glucose entry during a short time period after eating.
