Influence of Phenolic Acids on Rumen Fungi1
- Danny E. Akin and
- Luanne L. Rigsby2
Phenolic acids are associated with forage fiber, and in the free acid state have been shown to reduce in vitro fiber digestion by rumen bacteria. The objective of the study was to test the effect of free phenolic acids on the colonization and degradation of leaf blades by rumen fungi, which have been shown to attack lignified and other tissues. Colonization of leaf blades of ‘Coastal’ bermudagrass (Cynodon dactylon L. Pers.) by fungi was studied using the light microscope and digestibility was evaluated by dry weight loss. Reduction in the amounts of phenolic acids was determined using ultraviolet spectrophotometry at wavelengths characteristic for the acids. Colonization by rumen fungal populations from a steer (Bos spp.) eating bermudagrass or alfalfa (Medicago sativa L.) was evaluated in the presence of penicillin and streptomycin to inhibit growth of rumen bacteria. The addition of 0.1% .p-coumaric, ferulic, or sinapic acid to media reduced by at least two to three times the number of sporangia developing on the cut edges of leaf blades; the reduction was greater for the alfalfa inocula. Dry weight loss of leaf blade sections in the presence of acids was 25 to 50% of that without acids, and the reduction was greater with alfalfa inocula. No major differences in sporangial numbers or dry weight loss occurred among these acids. Reduction in spectral areas at characteristic wavelengths between uninoculated and inoculated tubes was 14 to 15% for p-coumaric and ferulic acid, but was 44% for sinapic acid. Phenolic acids similar to those in plant cell walls inhibited the development of sporangia on leaf blades and reduced fiber digestion by rumen fungi.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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