Lignin composition is more important than content for maize stem cell wall degradation

BACKGROUNDThe relationship between the chemical and molecular properties, in particular the lignin (ADL) content and composition expressed as the ratio between syringyl and guaiacyl compounds (S:G ratio), of maize stems and in vitro gas production was studied in order determine which is more important in the degradability of maize stem cell walls in the rumen of ruminants. Different internodes from two contrasting maize cultivars (Ambrosini and Aastar) were harvested during the growing season.RESULTSThe ADL content decreased with greater internode number within the stem, whereas the ADL content fluctuated during the season for both cultivars. The S:G ratio was lower in younger tissue (greater internode number or earlier harvest date) in both cultivars. For the gas produced between 3 and 20 hours, representing the fermentation of cell walls in rumen fluid, a stronger correlation (R2=0.80) was found with the S:G ratio than with the ADL content (R2=0.68). The relationship between ADL content or S:G ratio and 72-h gas production, representing total organic matter degradation, was weaker than that with gas produced between 3 and 20 hours.CONCLUSIONThe S:G ratio plays a more dominant role than ADL content in maize stem cell wall degradation.