Alteration of Rumen Fermentation in Steers by Increasing Rumen Fluid Dilution Rate with Mineral Salts

Abstract

Holstein steers were fed either high concentrate or high roughage diets ad libitum, and hypertonic solutions of either sodium chloride or sodium bicarbonate were infused intraruminally to increase osmotic pressure of the rumen fluid. Dry matter intake was reduced in steers fed the high roughage diet during the intraruminal infusion of 1kg of sodium chloride. Decreased cellulose degradation as a result of increased osmotic pressure of rumen fluid may have been responsible for the reduced dry matter intake. Dilution rate of rumen fluid was increased by infusion of both sodium chloride and sodium bicarbonate. An increase in water consumption accounted for, at least in part, the increase in total outflow of fluid from the rumen. The concentration of total volatile fatty acids in rumen fluid was reduced during infusion of both sodium chloride and sodium bicarbonate. The increased dilution rate of rumen fluid when hypertonic solutions were infused intraruminally into steers fed a high concentrate diet was associated with an increased molar proportion of acetate and a decreased molar proportion of propionate. In contrast, the molar proportions of acetate and propionate in the rumen fluid of steers fed a high roughage diet were not altered although dilution rate of rumen fluid was increased by infusing the hypertonic solutions.