Feed Intake, Apparent Diet Digestibility, and Rate of Particulate Passage in Dairy Cattle

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Abstract
Depression in digestibility of both diet and feed fractions were measured in 2 diets fed at 2 intakes to dairy cattle. A low forage diet of 32% forage and 68% concentrate (dry matter) and a high forage diet of 83% forage and 17% concentrate were fed to dry cows at maintenance and lactating cows at ad lib intake. Lactating cows consumed 42.1 and 32.2 g dry matter/kg body wt on the low forage and high forage diets, respectively; dry cows consumed 12.0 and 13.0, respectively. Energy digestibilities were 67.5 and 64.0% for lactating cows on the low forage and high forage diets and 73.7 and 67.6% for dry cows, respectively. Depressions in digestibility for dry matter, neutral detergent fiber, hemicellulose, cellulose, energy and cell solubles per unit of intake were greater on the low forage diet. Retention time of concentrate increased by 0.44 U for each unit increase in retention time of forage. Retention times in the total tract for forage and concentrates were 62 and 73% less, respectively, at low intake on the low forage diet. Similar results for the high forage diet were 80 and 81%, respectively. Retention times of concentrate and forage were correlated with digestibility of gross energy.