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Glucose Metabolism in Cows Fed Low— and High—Roughage Diets

Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1

ABSTRACT

Six lactating first-calf Holstein cows were used to test the effect of dietary roughage on glucose metabolism. Cows were fed either a low-roughage or high-roughage diet at isocaloric digestible energy intakes in a double changeover design experiment. Mean values (± standard deviation) for milk yield (kg/day), fat (%), lactose (%), and protein (%) for cows fed low-roughage were 19.0 ± 4.4, 3.11 ± .78, 5.19 ± .27, 3.44 ± .48; values for cows fed high-roughage were 17.5 ± 5.1, 3.99 ± .58, 4.94 ± .25, and 2.78 ± .33. One hour post-feeding on the 20th day of each period 2 mCi of tritiated glucose were administered to each cow by single injection to measure glucose kinetics. Mean values (± standard deviation) for plasma concentration (mg/100 ml) pool size (mg/kg), half-time (min), and utilization rate (mg/kg^.75 per min) of glucose, and plasma insulin concentration (µU/ml) for cows fed low-roughage were 63.1 ± 3.9, 17.9 ± 3.4, 30.4 ± 5.2, 8.55 ± 2.44, and 22.0 ± 3.9; for cows fed high-roughage values were 54.9 ± 2.2, 114.5 ± 17.2, 40.0 ± 2.2, 4.06 ± .38, and 16.1 ± 2.4. A glucose load was administered intravenously to each cow on the last day of each period. Glucose half-times and mean plasma insulin following the clearance test were not affected by diet. Compared to high-roughage, low-roughage diets greatly affect metabolism in lactating cows when isocaloric intakes of each are fed. Fat depression, however, may or may not occur simultaneously.