Release of ‘soluble’ lignin fragments from orchardgrass during its passage through the rumen

Soluble lignin fractions were isolated with 90% (v/v) aqueous dioxane from the rumen digesta and faeces of a heifer fed on orchardgrass harvested at the pre‐heading stage. Chemical analysis, UV and IR spectra indicated that the soluble lignin fractions were composed mostly of lignin components. The two solube lignin fractions showed wide distributions of molecular weight and had number‐average molecular weights of 650–690 and weight‐average molecular weights of 1450–1480. The results showed that, part of the orchardgrass lignin fed was released in the rumen as soluble lignin fragments with different molecular weights and excreted in the faeces possibly without further significant modifications.