Simple Phenolic Monomers of Forages and Effects of in Vitro Fermentation on Cell Wall Phenolics

Abstract

Alfalfa hay, soybean stover, smooth brome-grass hay and corn stalklage were analyzed for the presence of 11 simple phenolic monomers (p-coumaric, ferulic, gallic, p-hydroxybenzoic, protocatechuic, salicylic, syringic and vanillic acids, p-hydroxybenzaldehyde, syringaldehyde and vanillin) after ether and alkali extractions and nitrobenzene oxidation. Both intact forages and cell wall preparations were examined. No free, ether soluble, phenolic compounds were detected. Forages differed (P<.05) in content of alkali-labile monomers and most compounds occurred in both the cell soluble and cell wall fractions. Nitrobenzene oxidation products also varied (P<.05) among forages, but were apparently associated totally with cell walls. Concentrations of nitrobenzene oxidation products were unrelated to lignin content. Sheep fed these forages had low concentrations of soluble phenolic monomers in their rumen fluid. Phenolic monomer content of forages was related to concentrations of monomers in rumen fluid. In vitro dry matter disappearance and cell wall digestibility differed (P<.05) among forages, while apparent lignin digestibilities did not. Alkali extracted and nitrobenzene oxidized phenolic monomers had apparent digestibilities ranging from -69.5 to 74.1% and -440.6 to 52.7%, respectively. Digestion of specific phenolic monomers differed (P<.05) among forages. Phenolic monomers in fermentation supernatants differed (P<.05) among forages and recoveries of cell soluble phenolics ranged from -12.5 to 328.7%. Diet of donor animals from which rumen fluid was collected had no effect on any in vitro fermentation measurement. Copyright © 1983. American Society of Animal Science . Copyright 1983 by American Society of Animal Science.