Distribution of fermentative products and butyric/acetic acid ratio for the six TS contents tested. These metabolites were measured after 11 days of reaction, expressed in mole unit, and reported on the initial TS content of the straw. The sum of fermentative products indicates the straw conversion yield. The butyric/acetic acid ratio indicated a metabolic shift that occurred at 28% TS. TS, total solids.