title: Effects of diet forage-to-concentrate ratio and intake on energy metabolism in growing beef heifers: whole body energy and nitrogen balance and visceral heat production.
abstract: Effects of diet forage-to-concentrate ratio and intake on balances of energy and nitrogen and portal-drained viscera (PDV), liver and kidney blood flow and O2 consumption were measured in seven growing beef heifers. Isonitrogenous pelleted diets containing approximately 75% alfalfa or 75% concentrate were fed daily as 12 equal meals every 2 h at two isoenergetic metabolizable energy intakes. A split-plot design was used, with 4 wk for adaptation to diet followed by 3-wk intake periods within 6-wk diet periods. Heifers consumed and digested less dry matter, energy and nitrogen when fed the 75% concentrate vs. 75% alfalfa diet at equal metabolizable energy. Heifers fed the 75% concentrate diet produced less heat energy and retained more tissue energy than when fed the 75% alfalfa diet. Blood flow for PDV, liver and kidneys increased with intake and was greater when heifers were fed the 75% alfalfa vs. 75% concentrate diet. Increased PDV and liver O2 uptake accounted for 44 and 72% of heat increment for the 75% concentrate and 75% alfalfa diets, respectively. Greater PDV uptake of O2 accounted for 72% of the decrease in tissue energy of heifers fed the 75% alfalfa vs. 75% concentrate diet at equal metabolizable energy.
authors.affiliation: U.S. Department of Agriculture, Livestock and Poultry Sciences Institute, Beltsville, MD 20705.
authors.forename: C K
authors.initials: CK
authors.lastname: Reynolds
authors.forename: H F
authors.initials: HF
authors.lastname: Tyrrell
authors.forename: P J
authors.initials: PJ
authors.lastname: Reynolds
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001833:Body Temperature Regulation; D002417:Cattle / Q000254:growth & development*; D004032:Diet; D004734:Energy Metabolism; D005260:Female; D007668:Kidney / Q000098:blood supply / Q000378:metabolism; D008099:Liver / Q000098:blood supply / Q000378:metabolism; D000455:Medicago sativa; D009584:Nitrogen / Q000378:metabolism*; D010101:Oxygen Consumption
chemical_list: D009584:Nitrogen