Predicting in‐vivo digestibilities of herbages by exhaustive enzymic hydrolysis of cell walls

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Abstract
A potent cellulase solution was prepared from culture filtrates of an artificially‐produced mutant of Trichoderma species. The filtrates were diluted to provide a standardised, simulated rumen liquor which was then used to study the correlation between cellulase digestibility and in‐vivo digestibility of a range of plant materials. Cell walls of whole, dried plant material were either not attacked by the cellulase or were attacked only very slowly, but cell walls isolated by neutral‐detergent extraction were readily hydrolysed. Cellulase digestibility, defined as the percentage of whole, dry plant material solubilised by neutral‐detergent extraction followed by exhaustive hydrolysis with standardised cellulase, was highly correlated with in‐vivo dry matter digestibility (DMD) (r=0.98) and predicted that parameter with reasonable accuracy (r.s.d., residual standard deviation = 2.83). The form of the regression equation was in‐vivo DMD = 0.98 × cellulase solubility ‐ 10.12, suggesting that the same factors limited cellulase and in‐vivo digestibility. The method was simple and reliable and results were known within 48 h.