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

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 2mCi of tritiated glucose were administered to each cow by single injection to measure glucose kinetics. Mean values (± standard deviation) for plasma concentration (mg/100ml) 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.