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1 Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802
2 Bioproducts, Inc., Fairlawn, OH 44333
3 U.S. Dairy Forage Research Center, Madison, WI 53706
Corresponding author: G. A. Varga; e-mail: gvarga{at}psu.edu.
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.
Key Words: sucrose • continuous culture • ruminal fermentation • bacterial nitrogen
Abbreviation key: 0S = 7.5% corn starch + 0% sucrose treatment, 2.5S = 5% corn starch + 2.5% sucrose treatment, 5S = 2.5% corn starch + 5% sucrose treatment, 7.5S = 0% starch + 7.5% sucrose treatment, NSC = nonstructural carbohydrates.
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