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

Abstract Depressions in digestibility of both diet and feed fractions were measured in two diets fed at two 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 libitum intake. Lactating cows consumed 42.1 and 32.2 g dry matter/kg body weight on the low forage and high forage diets whereas dry cows consumed 12.0 and 13.0. 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. 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 .44 units for each unit increase in retention time of forage. Retention times in the total tract for forage and concentrates were 62 and 73% less at low intake on the low forage diet. Similar results for the high forage diet were 80 and 81%. Retention times of concentrate and forage were correlated with digestibility of gross energy.