|Brown, Kelly - UNIVERSITY OF KENTUCKY|
|Matthews, James - UNIVERSITY OF KENTUCKY|
|Boling, James - UNIVERSITY OF KENTUCKY|
Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2008
Publication Date: June 4, 2008
Citation: Flythe, M.D., Gellin, G.L., Klotz, J.L., Strickland, J.R., Brown, K.R., Matthews, J.C., Boling, J.A. 2008. The Effect of Toxic Tall Fescue on Cellobiose-Utilizing Populations in the Bovine Rumen. American Society for Microbiology Annual Meeting. ISBN 978-1555814939. Z-040 (Abstract CD). Technical Abstract: A fungal endophyte (Neotyphodium coenophialum) infects tall fescue (Schedonorus arundinaceus Schreb. Dumort), and confers pest resistance through the production of alkaloids. Although, these alkaloids can reach concentrations that are toxic to livestock, their effects on the symbiotic rumen bacteria are largely unknown. Cellobiose is a common intermediate in rumen fermentation, and this survey was initiated with the hypothesis that a component in the forage (i.e. an alkaloid) inhibits cellobiose-utilizing bacteria. Methods: Steers were maintained on low-endophyte (LE; n = 6) or high-endophyte (HE; n = 6) infected fescue pastures. Cellobiose utilizing bacteria were enumerated by dilution series. The isolates were identified by 16S rRNA sequence homology. Substrate utilization was determined with API 20A strips and HPLC. Growth experiments were conducted in broth that was amended with sterile rumen fluid. Results: When rumen fluid from steers grazing LE pastures was serially diluted into media with cellobiose, growth was observed at dilutions as great as 10-9. However, enumerations from steers grazing HE fescue indicated that 100 to 1000-fold fewer cellobiose-utilizing bacteria were present (P < .01). The numerically dominant bacteria were Streptococcus bovis in most cases, but bacteria related to Selenomonas ruminantium, Actinomyces ruminicola, and Lactobacillus vitalinus were also isolated. None of the isolates were inhibited by the presence of LE or HE rumen fluid. In most cases, the growth rates and optical densities were enhanced by the presence of either type of rumen fluid. Conclusion: These results indicate that similar bacteria occupied the cellobiose-utilizing niche in both LE and HE steers. Culture-based enumerations suggested that these populations were smaller in hosts exposed to toxic fescue. However, in vitro growth experiments did not reveal the presence of an inhibitory compound. Since feed intake is decreased in animals with fescue toxicosis, it is likely that the differences in cellobiose utilizing populations were due to nutrient limitation.