title: Effects of replacing dietary starch with sucrose on ruminal fermentation and nitrogen metabolism in continuous culture.
abstract: A dual-effluent continuous-culture system was used to evaluate the effects of partially replacing cornstarch with sucrose in a total mixed ration on ruminal fermentation and N metabolism. The 4 treatments were 0 (control), 2.5, 5.0, and 7.5% sucrose and, respectively, 7.5 (control), 5.0, 2.5, and 0% cornstarch in a total mixed ration containing 20% corn silage and 40% alfalfa silage. Fermenters were fed 4 times a day during four 9-d periods with sampling beginning on d 6. Replacing cornstarch with sucrose did not alter ruminal pH (5.97), total volatile fatty acids (VFA) (104.4 mmol/L), or the acetate to propionate ratio (2.16); however, branched-chain volatile fatty acids were higher for the control treatment compared with the 7.5% sucrose treatment. Five hours postfeeding, sucrose treatments significantly altered molar proportions of all volatile fatty acids, and acetate-to-propionate and glucogenic-to-lipogenic ratios. Digestibility of dry matter and N were not affected by treatment, but digestibility of total non-structural carbohydrates was increased with sucrose treatments. A quadratic effect was noted for neutral detergent fiber (NDF) digestibility as sucrose replaced starch. A higher NDF digestibility (66.1 vs. 59.9%) was observed for the 7.5% sucrose treatment compared with the other 2 sucrose treatments. Levels of ammonia N were within an acceptable range to support microbial protein synthesis and did not differ among treatments (mean=9.23 mg/dL). Sucrose inclusion in the total mixed ration did not affect bacterial N synthesis. Results indicate that (at the levels tested in this study) inclusion of sucrose in the diet when rumen-degradable protein is adequate does not affect ruminal fermentation.
authors.affiliation: Department of Dairy and Animal Science, The Pennsylvania State University, University Park, 16802, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Vallimont
authors.forename: F
authors.initials: F
authors.lastname: Bargo
authors.forename: T W
authors.initials: TW
authors.lastname: Cassidy
authors.forename: N D
authors.initials: ND
authors.lastname: Luchini
authors.forename: G A
authors.initials: GA
authors.lastname: Broderick
authors.forename: G A
authors.initials: GA
authors.lastname: Varga
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis; D002417:Cattle / Q000378:metabolism*; D004043:Dietary Fiber / Q000008:administration & dosage / Q000378:metabolism; D019422:Dietary Sucrose / Q000008:administration & dosage* / Q000378:metabolism; D004063:Digestion; D004305:Dose-Response Relationship, Drug; D005232:Fatty Acids, Volatile / Q000032:analysis; D005260:Female; D005285:Fermentation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007774:Lactation / Q000378:metabolism*; D000455:Medicago sativa; D009584:Nitrogen / Q000378:metabolism; D012417:Rumen / Q000737:chemistry / Q000378:metabolism* / Q000382:microbiology; D012820:Silage; D013213:Starch / Q000008:administration & dosage* / Q000378:metabolism; D003313:Zea mays
chemical_list: D001426:Bacterial Proteins; D004043:Dietary Fiber; D019422:Dietary Sucrose; D005232:Fatty Acids, Volatile; D013213:Starch; D009584:Nitrogen