KINETICS OF CELL-WALL DIGESTION OF ORCHARDGRASS AND ALFALFA SILAGES TREATED WITH CELLULASE AND FORMIC-ACID

The objectives of this study were to determine the effects of cellulas e (from Trichoderma longibrachiatum) combined with formic acid, applie d before ensiling, on the subsequent concentration and composition of the cell wall and on the extent and rate of in situ cell-wall digestio n of orchardgrass (Dactylis glomerata L.) and alfalfa(Medicago sativa L.). Treated and control forages of both plant species were ensiled fo r at least 60 d before being ruminally digested by two fistulated cows . Analyses of NDF, ADF, and acid detergent lignin were conducted seque ntially on original and digested samples. Data were fitted with a firs t-order, nonlinear model to estimate extents and rates of digestion of potentially digestible NDF, cellulose, and hemicellulose. The concent ration of indigestible residue and the discrete lag time before digest ion were also determined for the cell-wall components. After ensiling, the mean NDF concentration of treated silages was 19% lower than that of control silages; the effect was greater for orchardgrass than for alfalfa. The extent of digestion of NDF, cellulose, and hemicellulose, respectively, was 33, 37, and 27% lower for treated silages than for control silages. Treatment effects on the extent of digestion varied b etween plant species. Cellulose from treated orchardgrass was digested 19% more slowly than cellulose from the control silage. Indigestible residue concentrations of NDF, cellulose, and hemicellulose, respectiv ely, were 7, 8, and 7% lower in treated silages than in control silage s. Thus, extensive cell-wall degradation by cellulase during ensiling resulted in less digestible cell-wall material for ruminal digestion b ut greater total cell-wall degradation, including that during ensiling and ruminal incubation, especially during early digestion in the rume n.