Effects of Intake of a Mixed Diet by Dairy Steers on Digestion Events

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Abstract
Ruminally cannulated steers were in a 4 .times. 4 Latin square to determine the effect of amount of feed ingested on fiber digestion and other digestion events. Alfalfa haylage, corn silage, and a corn-soybean meal mix were incorporated in a ratio 45:20:35 (dry matter) and fed at either 100, 85, 70 or 55% of ad lib intake. Acid-insoluble ash, lanthanum, and Cr-EDTA were digestion, particulate and liquid markers. Apparent digestibility of dry matter, neutral detergent fiber, and cell solubles decreased linearly as feed intake increased. The fiber fraction digested was a larger percentage of the dry matter digested at low than at high intakes of feed. A more rapid rate of cellulose disappearance and a slow rate of passage of particular matter through the rumen and total digestive tract with decreasing feed intake were key factors responsible for bringing about changes of digestion coefficients. A consistently lower rumen pH of steers at high intakes of feed probably accounted for the slower rate of ruminal fiber disappearance. The lower tract accounted for 11-17% of dry matter disappearance, and tended to play a greater role during periods of high feed intake. Rumen and fecal sampling techniques provided similar ruminal rates of solids passage.