Regulation of Food Intake in Ruminants. 2. Rations Varying in Energy Concentration and Physical Form

Abstract

Eight rations varying in physical form and energy concentration were fed to 12 Holstein heifers in a partially balanced incomplete block design. Total ration dry matter intake was increased when pelleted corn was fed with long oat straw and long alfalfa hay compared to the roughages fed alone. Grinding of the oat straw decreased intake, whereas grinding and pelleting of the alfalfa hay increased consumption. Pelleted rations composed of 50% roughage and 50% corn resulted in higher digestible energy intake than the corresponding ground or pelleted roughages. Addition of corn to the roughage diets increased dry matter digestibility, decreased the digestibility of cellulose, and increased rumen retention time for the roughage part of the diet. Gastrointestinal tract fill increased as dry matter intake increased. The data indicated that a more accurate method of estimating the space-occupying characteristics of a feed is needed in order to verify the bulk or rumen load theory of food intake regulation in ruminants.