NUTRIENT YIELDS FROM IN VITRO FERMENTATIONS OF SUCROSE AND NEUTRAL DETERGENT FIBER BY MIXED RUMINAL MICROORGANISMS

Authors: HALL, M - U OF FL, GAINESVILLE; Weimer, Paul

Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/25/2002
Publication Date: 7/25/2002
Citation: Hall, M.B., Weimer, P.J. 2002. Nutrient yields from in vitro fermentations of sucrose and neutral detergent fiber by mixed ruminal microorganisms [abstract]. Journal of Dairy Science. p. 183.

Interpretive Summary:

Technical Abstract: The effect of level of sucrose on nutrient yield by mixed ruminal microbes was evaluated in vitro in two 24 h fermentations in sealed vials. Isolated bermudagrass (Cynodon dactylon) NDF (130 mg) was incubated with sucrose (Suc; 65, 130, or 195 mg) in Goering/Van Soest buffer with 15% ruminal fluid (total volume 32 ml/vial). Vials for each level of sucrose were destructively sampled at 0, 4, 8, 12, 16, 20, and 24 h, and were analyzed for microbial crude protein (MCP), dextran, organic acids, and residual sucrose, glucose (Glc) and fructose (Frc). To estimate MCP, vial contents were precipitated at a concentration of 20% trichloroacetic acid (TCA), and filtered to collect unfermented NDF and precipitate. Collected residues were analyzed for crude protein (CP) as combustion N x 6.25. MCP was estimated at TCA-precipitated CP corrected for the TCA-precipitated CP content of the substrates at 0 h, and the mean of fermentation blanks from each hour. Significance was declared at P<0.05. Least-squares mean values are reported. MCP yield increased linearly with increasing Suc, but mg MCP/mg Suc declined linearly. MCP yield peaked at the 8 h sampling, and exhibited a slow decline through 24 h. No Suc was detected in the media at 0 h. Frc declined to undetectable levels by 4 h. Glc exhibited a similar decline, but was detected through 4 or 8 h. Dextran yield increased linearly with increasing Suc and peaked at 4 h. The proportion of Suc converted to dextran decreased with increasing Suc. The pH at 24 h declined linearly with increasing Suc (6.28, 6.14, and 5.94, respectively). Organic acids increased rapidly to 4 h then linearly but more slowly through 24 h. Organic acid yield at 24 h increased linearly with Suc. At 24 h, molar percentages of acetate decreased linearly, propionate increased quadratically, and butyrate increased linearly with increasing Suc. Lactate was transiently observed at 4 h. Lactate yield increased quadratically with increasing Suc. Total nutient yield (mg MCP+dextran+organic acids)/mg Suc at 24 h increased linearly as Suc increased (1.17, 0.89, and 0.79, respectively). Thus, increasing Suc supplementation increased nutrient yield, decreased yield of nutrients/mg Suc, and altered the profile of organic acids produced.