Availability and Metabolism of Various Substrates in Ruminants. IV. Glucose Metabolism in the Young Calf and Growing Steer

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Abstract
The glucose pool size, rate of utilization, and glucose space were measured in 3 young calves and 3 growing steers, using an isotope dilution technique. The pool size of glucose, when expressed in terms of grams/100 lb of body weight, was found to be 41% greater in the calves than in the steers, which agrees in mangnitude with the recognized differences in whole blood glucose concentrations between young and older animals. These data suggest that differences in blood glucose concentrations reflect differences in pool size. The mean glucose space was approximately 11% higher in the calves than in the steers, averaging 32.0 and 20.7% of the body weight, respectively. These data indicate that the glucose space involves only the extracellular fluids. Glucose was utilized at a rate of 8.3 g/hr/100 lb of body weight by the calves, whereas for the steers it was 4.7. This represents a 43% decrease in the rate of glucose utilization by the older animals and is of the same magnitude as the 41% difference obtained in pool size. These data are interpreted as suggesting that glucose utilization is dependent upon the amount available to the tissue.