Abstract: | Experiments were conducted to determine whether formation of quinone methide intermediates from lignin occurs during ruminal fermentation of corn stover, as indicated by nucleophilic addition reaction with sulphur-containing reducing agents. Corn stover leaf and stem fractions harvested at full maturity were incubated in buffered ruminal fluid without reducing agents or with (NH4)2SO4 (S-control), Na2S.9H2O, cysteine-HCl (cysHCl), or cysHCl plus Na2S.9H2O; and in only buffer with or without cysHCl plus Na2S.9H2O. Mixed reducing agents (cysHCl plus Na2S.9H2O) enhanced ( P< 0.001) in vitro fibre degradation after 48 h, tended to increase solubilisation of fibre ( P =0.07) and dry matter ( P =0.06) in buffer alone, and elevated ( P< 0.001) S-content of residual fibre. In vitro incorporation of S into the undegraded fibre was determined for corn stover fractions of varying lignin compositions that were harvested at two maturities (early dent and full maturity) in 2 years. Extent of fibre degradation was correlated with extent of S-incorporation ( r =-0.54, P< 0.001), and with lignin methoxyl content ( r =-0.84, P< 0.001). The negative association of lignin methoxyl content with digestibility is explained by the relative likelihood of quinone methide intermediate formation from guaiacyl and syringyl units in lignin. |