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 eight cows, four first lactation and four second or later lactation. Diets were fed for ad libitum intake in two periods of 21 d 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 versus 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.