INFLUENCE OF FEED PARTICLE SIZE ONpH, CARBOHYDRATE CONTENT, AND VISCOSITY OF RUMEN FLUID

Four fistulated cows were used to compare the rumen fluid properties produced from feeding all-concentrate feeds of fine (344 μ), or coarse (519 μ) geometric mean particle size, or alfalfa hay. A severe frothy condition developed in the rumens of cows fed the fine particle size feed but not in the rumens of cows fed the coarse or hay diets. The average viscosity of rumen fluid from cows fed hay was 7.4 centipoises (cP), about 14.7 cP when fed the coarse feed, and about 30.7 cP when fed the fine feed. After the cows became accustomed to their feed, rumen fluid pH declined from 6.5 to 5.6 when fed the fine particle feed and from 6.9 to 6.0 when fed the coarse. The rumen fluid from the cows fed the fine feed exhibited two viscosity maxima, between pH 5.5 and 5.8, and between pH 7.5 and 8.5, whereas the viscosity of the rumen fluid from the cows fed the coarse feed was not influenced by pH. Soluble carbohydrate levels were 650 μg/ml in the rumen fluid of cows fed the coarse-particle diet and over 1,000 μg/ml in that from cows fed the fine-particle feed. Cows fed hay had less than 300 μg/ml of soluble carbohydrate in the rumen fluid.