Effects of diet and energy intake on kinetics of glucose metabolism in steers.
To test the hypothesis that glucose utilization in ruminants is related to energy consumption independent of diet composition or energy content, eight Holstein steers (165-230 kg) were fed either a high grain (70% corn, 20% alfalfa, 8.8% soybean meal) or high hay (70% alfalfa, 28% corn) diet. The two diets were fed in quantities that allowed comparisons to be made either isocalorically based on calculated net energy for gain (NEg) or at identical dry matter intakes. The daily ration was divided into 12 equal portions and dispensed every 2 hours by automatic feeders to achieve steady-state conditions with respect to glucose metabolism. After adaptation to the dietary regimen, rates of glucose irreversible loss were measured following a single injection of 500 muCi of [6-3H]glucose. Glucose irreversible loss also was measured after a 7-day fast. Glucose irreversible loss was equal when both diets were fed isocalorically, was larger among steers fed the grain diet when comparisons were made at equal intakes of dry matter, and increased when the intake of either diet was increased. The increase in glucose irreversible loss with increasing energy intake showed a highly significant linear relationship over the range of intakes for both diets. It was concluded that energy intake, in contrast to diet composition, is responsible for the regulation of glucose irreversible loss.