|Jung, Hans Joachim|
Submitted to: Netherlands Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2004
Publication Date: 10/1/2004
Citation: Jung, H.G., Engels, F.M., Weimer, P.J. 2004. Degradation of lucerne stem cell walls by five rumen bacterial species. Netherlands Journal of Agricultural Science. 52:11-28. Interpretive Summary: Alfalfa is the most important forage crop fed to dairy cows in the United States. The nutritional value of alfalfa is limited by the poor digestibility of the fiber fraction in stems of this plant. Cows depend on bacteria present in their rumen, the largest of the four stomachs, to digest fiber. While there are many types of fiber digesting bacteria in the rumen, relatively little is known about these bacteria concerning how they differ in their ability to digest the fiber in alfalfa. We found that one specific bacterium, Ruminococcus albus, was able to digest all the fiber fractions in alfalfa stems better than four other common rumen bacteria. This bacterium alone was as efficient at digesting alfalfa fiber as a sample of the total mixed rumen bacteria population collected from a cow. The other rumen bacteria tested were able to digest some fiber fractions reasonably well but could not effectively digest cellulose, the most common type of fiber in alfalfa. These results suggest that manipulation of the rumen environment to increase the number of Ruminococcus albus bacteria offers the potential to improve alfalfa fiber digestion by dairy cows. Microbiologists developing rumen-modifying additives now have a clear target to enhance fiber digestion capacity in the rumen of cattle.
Technical Abstract: The rumen bacterial strains Butyrivibrio fibrisolvens H17c, Fibrobacter succinogenes S85, Lachnospira multiparus 40, Ruminococcus albus 7, and R. flavefaciens FD-1 were compared with a rumen inoculum for ability to degrade alfalfa cell wall polysaccharides individually and as a five-species mixture. Two maturity stages of alfalfa (bud and full flower) and incubation periods of 24 and 96 h were examined. Alfalfa stems and fermentation residues were analyzed for cell wall concentration and composition. Cell wall glucose was considered to represent the cellulose fraction; the sum of xylose, mannose, and fucose residues composed the hemicellulose fraction; and pectin was the sum of uronic acids, galactose, arabinose, and rhamnose residues. Degradation of total cell wall polysaccharides and of all polysaccharide fractions of the immature alfalfa stems was greater than for the mature stems. The 96-h incubation period resulted in more degradation of all cell wall polysaccharides than did the 24-h incubation. The R. albus culture was able to degrade all cell wall polysaccharide fractions as well or better than any other culture, including the rumen inoculum. Co-culture of R. albus with the other four ruminal species did not improve degradation of any of the cell wall polysaccharides when compared to R. albus alone. Microscopic examination of stem thin sections indicated that R. albus and the five-species mixture appeared to be able to degrade alfalfa tissues to almost the same extent as did rumen fluid.