Evaluation of Marketed Cellulases for Activity and Capacity to Degrade Forage1

Abstract

AbstractCellulase‐solubility procedures provide an alternative method for evaluating forage digestibility; however, variable activities of marketed cellulase preparations complicate determination of optimum enzyme‐substrate proportions. This study was conducted to evaluate and compare exo‐ (Cl) and endo‐ (Cx) β‐1,4‐glucanases plus β‐glucosidase, and filter paper (FP) activities of various cellulase preparations and the capacity of these preparations to degrade forage. The use of cellulase in an in vitro forage digestibility assay based on FP activity units was also examined. Cellulase components (i.e., Cl, Cx, and β‐glucosidase) and FP activities were determined in four marketed cellulase preparations using established procedures. Supplemental additions of a marketed β‐glucosidase preparation to cellulase digestions were also evaluated. The cellulase preparations exhibited considerable differences in component enzyme activities and these differences were reflected in estimates of FP activity and the capacity of the cellulases to degrade forage. High levels of forage degradation were associated with high Cl/Cx activity ratios. Separate additions of β‐glucosidase did not increase forage degradation over that of the cellulase used alone. Cellulase‐solubility of 30 warmseason and 27 cool‐season grasses was highly correlated with rumen fermentation in vitro dry matter digestibility. Cellulase‐solubility values were generally lower than those obtained by the rumen fermentation method, however, Spearman rank‐order correlations indicted similar sample rankings by either assay method. The results indicate that component enzyme activity is highly variable among marketed cellulases and these differences influence the capacity of enzyme preparations to degrade forage. Filter paper activity units may be used to determine optimum enzyme‐substrate proportions in a digestibility assay; however, cellulase‐solubility methods which utilize marketed enzyme preparations may be more suitable for applications in which prediction of absolute in vivo digestibility values is less important than detection of relative differences.