1. Glucose entry rates were measured with [2−3H]glucose in groups of cattle given sugar-cane diets and between o and 1200 g rice polishings.
2. In the first experiment measurements of glucose metabolism were estimated in four animals (one of each being given 0, 400, 600 and 1000 g supplement) over 24 h using a repeated single injection at 6 h intervals and sampling blood for 3 h.
3. The results indicated that in a short time period of each isotope experiment relatively steady-state conditions existed since the plot of log specific radioactivity v. time was linear with a high correlation coefficient.
4. The pattern of glucose entry rates was variable over the 24 h period being highest shortly after feeding and then declining to quite low levels immediately before the next feed, 24 h later. However, the more rice polishings that were made available to the cattle, the higher the glucose entry rate at 4–7 h, and it remained higher for a longer time.
5. In the second experiment with nineteen animals there was a linear relationship between the glucose entry rate (measured 4–7 h after feeding) and the amount of rice polishings consumed by the animal.
6. The results suggest that glucose is being made available in quite large quantities from the supplement. Using the means of these estimates over 24 h to predict glucose entry rate on a daily basis, it is suggested that at least 50% of the starch in the rice polishings was made available to the animal as glucose.
7. The results are discussed in relation to the suggestion that the availability of glucose may be limiting nutrient in cattle given low-protein diets.