title: Effects of diet forage-to-concentrate ratio and intake on energy metabolism in growing beef heifers: net nutrient metabolism by visceral tissues.
abstract: Effects of diet forage-to-concentrate ratio and intake on metabolism of nutrients by portal-drained viscera (PDV), liver and kidneys were measured in seven growing beef heifers. Isonitrogenous pelleted diets containing approximately 75% alfalfa or 75% concentrate were fed every 2 h at two metabolizable energy intakes. Greater intake increased net PDV removal of glucose and urea nitrogen and net PDV release of NH3N, alpha-amino nitrogen (AAN), alanine and lactate. Lower net PDV release of NH3N, liver removal of NH3N and AAN and liver release of urea nitrogen accompanied lower N intake and digestion in heifers fed the 75% concentrate vs. the 75% alfalfa diet. Lower net PDV glucose removal resulted in greater total splanchnic glucose release when heifers were fed the 75% concentrate vs. the 75% alfalfa diet. In addition, net PDV, liver and total splanchnic release of beta-hydroxybutyrate (BOHB) were lower when heifers were fed the 75% concentrate vs. the 75% alfalfa diet. Greater tissue energy retention in heifers fed the 75% concentrate vs. the 75% alfalfa diet at equal metabolizable energy intake accompanied differences in net PDV metabolism of glucose, NH3N and BOHB and liver metabolism of nitrogenous compounds, BOHB and lactate.
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; D002417:Cattle / Q000254:growth & development*; D004032:Diet; D004734:Energy Metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism; 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: D005947:Glucose; D009584:Nitrogen