Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/22/2002
Publication Date: 7/22/2002
Citation: Weimer, P.J., Hall, M.B. 2002. Gas production kinetics and fermentation end product formation from neutral detergent fiber and sucrose by mixed ruminal microorganisms in vitro [abstract]. Journal of Dairy Science. p. 361. Interpretive Summary:
Technical Abstract: The effect of sucrose on neutral detergent fiber (NDF) digestion by mixed ruminal microflora was determined using an in vitro 40-channel gas pressure measurement system with computerized data acquisition. Isolated bermudagrass NDF (4 mg/ml) was incubated in 8.5 ml of Goering/Van Soest (pH 6.8) buffer amended with 1.5 mL of blended and squeezed ruminal fluid and varying amounts of sucrose (0, 2, 4, or 6 mg/ml, six replicates per treatment). Additional sets of vials contained no added substrate (blanks), or 6 mg sucrose/ml without NDF. Gas production data from 153 to 178 data points collected over a 48h period were blank-corrected and fitted to single-pool (NDF or sucrose alone) or dual-pool (NDF + sucrose) exponential models that incorporated one or two discrete lag terms, respectively. Sucrose concentration had no effect on the rate constant of gas release from either sucrose (0.29-0.30/h) or NDF (0.053/h). Lag times for gas release from NDF digestion increased markedly with sucrose concentration (4.3, 8.0, 10.4, and 13.0 h at 0, 2, 4 and 6 mg sucrose/ml, respectively; P < 0.05). Acetate comprised a smaller proportion of total VFA as sucrose increased (0.66 and 0.59 at 0 and 6 mg sucrose/ml, respectively; P < 0.05), while the proportion of butyrate increased (0.07 and 0.12 at 0 and 6 mg sucrose/ml, respectively; P < 0.05). Values for pH at 48h decreased (P < 0.01) with increasing sucrose (6.65, 6.46, 6.25 and 6.04 at 0, 2, 4 and 6 mg sucrose/ml, respectively). The data support the hypothesis that the rate constant of fiber digestion is dependent on the pH at which the fermentation is initiated.