Lignin and Methoxyl Groups as Related to the Decreased Digestibility of Mature Forages

Abstract

In an attempt to explain the decreased digestibility of cellulose in forages of advancing maturity, a study was made of the lignin and methoxyl content of two brome grass hays, two orchard grass hays and four timothy hays which were cut at different stages of maturity. The lower digestibility in vitro of the second stage orchard and brome grass hays relative to that of the less mature first stage could not be explained in terms of proximate composition or lignin content. In contrast, decreasing cellulose digestibility in the case of the four timothy hays, did appear to be related to lignin content and especially to acid-insoluble lignin expressed as a percentage of total lignin. When the acid-insoluble lignin of the brome and orchard grass hays was expressed as a percentage of total lignin, the percentage acid-insoluble lignin was higher in the brome grass hays than in the orchard grass hays showing an association between higher acid-insoluble lignin values and decreased cellulose digestibility. It was also observed that the level of “non-lignin” methoxyl in the brome grass hays was almost double that in the orchard grass hays. It is concluded that in the mature brome and orchard grass hays studied, the differences in the lignin content of hays cut at different stages are too small to account for the observed differences in the digestibility of the cellulose.