Feed Strategy - July 2018 - 37
FeedStrategy ❙ 37
but also the microbes themselves
- meaning ruminant agriculture
can produce human-edible products from human-inedible forage.
The rumen essentially acts as
a large fermentation vessel where
bacteria, protozoa and fungi digest
and degrade fibrous and nonfibrous plant material, as well as
protein and non-protein nitrogen
sources. There is also digestion and
modification of lipids by bacterial
lipases and biohydrogenation.
End products of rumen fermentation are either absorbed
directly through the rumen wall,
for example volatile fatty acids
(VFA), or in the small intestine
(SI), for example small peptides/
amino acids and lipids. Dead microbes are also washed through
the forestomach and can be digested and absorbed in the SI and
provide a significant contribution
to the host's nitrogen requirement.
The rumen ecosystem is
made up of four groups of microbes: bacteria, protozoa, fungi
and archaea. There are also bacteriophages, mycoplasmas and
archaeophages. In terms of numbers, bacteria are by far the most
abundant at 1010-1011 cells/ml,
followed by archaea (106-108
cells/ml), protozoa (105 cells/
ml) and fungi (103-105 cells/ml).
Bacteria comprise about twothirds of the rumen microbial
biomass with protozoa making
up to 50 percent due mainly to
July 2018 ❙ www.WATTAgNet.com
Examination of rumen
Since the 1980s, modern molecular techniques have allowed
us to better understand the role
of the microbial ecosystem and
particularly the diversity within it.
The 16S rRNA gene was a breakthrough in terms of being able
to catalogue changes in bacterial
communities because of different
rumen environments, including
diets. Pyrosequencing of a specific
region of the 16S rRNA gene allows
taxonomic classification of rumen
bacteria and the ability to evaluate
bacteria diversity in the rumen.
more than 60 percent of the
total bacterial samples they
sequenced. The authors noted
these groups comprised of three
known groups (Prevotella,
Butyrivibrio, and Ruminococcus),
as well as four unclassified
and Clostridiales), but the relative
abundance differed for all seven
across species. They hypothesized
that even though we can identify
the "core" species, more research
is required in order to understand
them and their role in the microbial community.
Climate change increasing heat stress
in dairy cows: www.WATTAgNet.
While much research has historically focused on individual strains,
recent research has started to look at
the bacterial community as a whole
in response to changes in rumen environment, namely dietary changes.
Bacteria are a diverse, plastic
group with a core community that
appears relatively consistent across
diets. Studies of rumen bacteria
have shown three major phyla that
comprise the core community, irrespective of diet: Bacteriodetes,
Firmicutes and Proteobacteria.
A large-scale study examining microbial communities
across a range of ruminant and
camelid species, diets and geographical regions found seven
bacterial groups accounted for
Similarly, an earlier metaanalysis revealed 19 bacterial
phyla present in the rumen microbiome. According to this metaanalysis (Ribosomal Database
Project), 71 percent of the bacterial species have been covered,
meaning that 30 percent remain
A core microbiome notwithstanding, diet appears to have a
major effect on bacterial diversity.
Across regions, communities from forage-fed animals
were similar but distinct from
concentrate-fed animals, which
were similar to each other. Both
were distinct from those fed
mixed diets, which were intermediate between the forage-fed and