Effects of Replacing Dietary Starch with Sucrose on Ruminal Fermentation and Nitrogen Metabolism in Continuous Culture

• Published in: Journal of dairy science 2004-12, Vol.87 (12), p.4221-4229
• Main Authors: Vallimont, J.E., Bargo, F., Cassidy, T.W., Luchini, N.D., Broderick, G.A., Varga, G.A.
• Format: Article
• Language: English
• Subjects: ammonium nitrogen; Animal Feed; Animal Nutritional Physiological Phenomena; Animal productions; Animals; bacterial nitrogen; Bacterial Proteins - biosynthesis; Biological and medical sciences; Cattle - metabolism; continuous culture; corn starch; Dietary Fiber - administration & dosage; Dietary Fiber - metabolism; Dietary Sucrose - administration & dosage; Dietary Sucrose - metabolism; Digestion; Dose-Response Relationship, Drug; Fatty Acids, Volatile - analysis; Female; Fermentation - drug effects; Food industries; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; in vitro digestibility; In Vitro Techniques; Lactation - metabolism; Medicago sativa; Nitrogen - metabolism; Rumen - chemistry; Rumen - metabolism; Rumen - microbiology; rumen fermentation; ruminal fermentation; Silage; Starch - administration & dosage; Starch - metabolism; Starch and starchy product industries; sucrose; Terrestrial animal productions; Vertebrates; Zea mays
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.S0022-0302(04)73567-5

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) (104.4mmol/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=9.23mg/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.