EFFECTS OF FEEDING CORN OR BARLEY ON COMPOSITION OF MILK AND DIET DIGESTIBILITY

Complete mixed, cubed diets containing corn or barley as the cereal component were fed to 8 cows, 4 first lactation and 4 second or later lactation. Diets were fed for ad libitum intake in 2 periods of 21 days each. Percentages of milk fat, protein, lactose and solids were not affected by corn or barley. Percentages of casein, whey and nonprotein nitrogen were not different nor was proportion of total nitrogen represented as casein, whey or nonprotein nitrogen for corn or barley diets. Production status, first lactation vs. older cows, did not affect milk composition of casein, whey and nonprotein nitrogen. Apparent digestibility of dry matter and energy was not different, but fiber digestibility was significantly lower for the barley diet. Intake of dry matter and digestible energy and yield of milk and milk constituents were not different. When diets were fed to rumen fistulated heifers molar percentages of volatile fatty acids, total volatile fatty acid concentration, and pH of rumen fluid were not different for corn or barley diets.