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Forage Cell Wall Degradation and -Coumaric, Ferulic, and Sinapic Acids¹

Phenolic acids are associated with carbohydrates in forage cell walls. Since phenolic compounds are often toxic to microorganisms, the objective was to test -coumaric, ferulic, and sinapic acids for their effect on rumen bacterial growth (turbidity and roll tubes), rumen protozoal motility, cellulose (filter paper) degradation, and cell wall digestion using light microscopy. The addition of 0.1% -coumaric acid to the media inhibited the growth of cellobiose-utilizing bacteria and increased the days required for cellulose degradation by two to three times. This acid also inhibited the growth of xylan-utilizing rumen bacteria, and caused a reduction of about 50% of the colonies appearing on xylan roll tubes. The percent motility of the entodiniomorph protozoa, but not the holotrichs, decreased more rapidly with time in the medium with -coumaric acid than in control medium. Sinapic acid was not toxic in any of the tests. Ferulic acid slowed the growth rate of rumen microorganisms on a habitat-simulating broth medium, but had little or no effect on cellulose-utilizing microorganisms. Ferulic acid did reduce slightly the growth of xylan-utilizing microbes in some tests. At the 0.2% level, -coumaric but not ferulic acid prevented the degradation of mesophyll and epidermis that were normally easily digested in orchardgrass (Dactylis glomerata L.) leaf blades. The results showed that -coumaric acid was toxic to certain rumen protozoa and the rumen bacteria expected to play a dominant role in the digestion of forage cell walls.

Key Words: Rumen microbial growth • Cellulose degradation • Dactylis glomerata L. • Phenolic acids

² Microbiologist, Field Crops Unit, Richard B. Russell Agric. Res. Center, IJSDA-ARS, Athens, GA 30613.

Received for publication June 29, 1981.