|MERTENS, DAVID - Former ARS Employee|
|Hall, Mary Beth|
Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2011
Publication Date: 9/1/2011
Citation: Weimer, P.J., Stevenson, D.M., Mertens, D.R., Hall, M. 2011. Fiber digestion, VFA production, and microbial population changes during in vitro ruminal fermentations of mixed rations by monensin-adapted and unadapted microbes. Animal Feed Science And Technology. 169:68-78.
Interpretive Summary: Studies on the digestibility of forages and activity of rumen microorganisms are often carried out by incubating samples from the rumen in the laboratory under controlled conditions. We examined the effects of several incubation conditions on forage fiber digestion and the populations of specific rumen microbes following such incubations. We observed that microbial population changes varied little despite substantial differences in incubation conditions, and that the relative population sizes of several bacterial species differed greatly from the original populations in the rumen. The results will be useful to scientists studying rumen microorganisms, and they suggest that such "in vitro" laboratory experiments may not adequately simulate the actual rumen situation.
Technical Abstract: Mixed ruminal microbes were incubated for 24 h in vitro with mixed forage and concentrate rations containing 20% or 30% non-fiber carbohydrates (NFC) to assess in vitro fiber digestibility, fermentation end products, and relative population sizes (RPS, expressed as a percentage of 16S rRNA gene copies determined by quantitative real-time PCR) of various bacterial taxa. Several taxa displayed substantial decreases in RPS (genus Prevotella, three Prevotella species, Rumincoccus flavefaciens, Eubacterium ruminantium, and Butyrivibrio fibrisolvens), while two (Rumincocccus albus and Megasphaera elsdenii) displayed substantial increases. RPS of 7 other taxa were not changed after the same incubation period. Among incubations containing 30% NFC, shifts in RPS were remarkably independent of fermentation conditions (initial pH 6.2 vs. 6.8, or 0% vs 1% corn oil). Similar in vitro experiments with the same ration in the presence of monensin, and using inocula from the same cows following adaptation to monensin, revealed RPS patterns generally similar to those of unadapted inocula without monensin. Within the range of conditions tested, monensin improved in vitro fiber digestibility regardless of environmental conditions, but significant changes in fermentation end-product formation were only observed at the higher NFC level in combination with the lower pH, and this effect was enhanced by the presence of corn oil. The data indicate that in vitro conditions can substantially change the quantitative distribution of microbial populations, and that these changes are both inherent in the in vitro method, and distinct from specific differences in divergent in vitro environmental conditions.