The cellulose-lignin complex in forages and its relationship to forage nutritive value

Abstract

SUMMARY The relationships between the cellulose-lignin complex, voluntary consumption and dry-matter digestibility were examined using forages of two varieties of Italian ryegrass and two legumes, lucerne and sainfoin. These forages had previously been shown to exhibit different intake-digestibility relationships. The cellulose, acid detergent lignin and acid detergent fibre contents of these forages as well as their digestibility coefficients were determined. Lignins were extracted from the fibre fractions and their ultraviolet difference spectra determined. Changes in maturity of a forage during a single growth phase, produced changes in dry-matter digestibility which were closely associated with changes in the digestibility of the cellulose and inversely related to the lignin content of the forage. Differences in digestibility between varieties of forage were less closely associated with lignin content. As the grasses matured a lignin fraction forming a difference peak at 350 mμ became evident and this was associated with decreased cellulose digestibility. Differences in voluntary food consumption resulting from changes in maturity of a single forage variety, in one growth phase, were also closely correlated with both dry matter and cellulose digestibility and inversely with lignin content. Differences between varieties and growth phases of the ryegrasses and between grasses and legumes were related less to the nature of the cellulose-lignin complex and more closely to the percentage of the total digesta deriving from cellulose. Sainfoin was characterized by the formation post-ruminally of an artifact that analysed quantitatively as lignin and qualitatively resembled a non-conjugated phenolic lignin fraction. The production of this artifact apparently disturbed fibre digestibility estimates and may have affected dry-matter digestibility estimates. Degradation of lignin apparently occurred both in the rumen and in the hind gut.