Influence of heat sterilization and ammoniation on straw composition and degradation by pure cultures of cellulolytic rumen bacteria

Abstract

Untreated and ammoniated straw was incorporated into culture medium, sterilized by autoclaving, and incubated with pure cultures of the predominant cellulolytic rumen bacteria: Bacteroides succinogenes, Ruminococcus flavefaciens and Ruminococcus albus or mixed rumen liquor micro-organisms for up to 8 days. The residues from the incubations and the water-insoluble fraction of the original straws were analysed for neutral sugar residues and Klason lignin. The relative disappearance of dry matter, cellulose and arabinoxylans was compared with the pattern of straw digestion in vitro. Sterilization by autoclaving solubilized 17 and 8% of the arabinoxylans and 9 and 4% of the glucans in the untreated and ammonia-treated straw, respectively. About 13% of the Klason lignin in the untreated straw and 8% in the ammoniated straw was also solubilized. Ammoniation did not alter either the composition or the relative degradation of insoluble straw polysaccharides, but increased the potential degradability by about 20%. All the bacterial preparations solubilized substantial fractions of both straw cellulose and arabinoxylans. However, mixed rumen liquor micro-organisms and B. succinogenes solubilized the two carbohydrate constituents equally, whereas the ruminococci preferentially solubilized the arabinoxylans.