Feed Strategy - July 2018 - 38
38 ❙ FeedStrategy
Cellulolytic bacteria, such as
Bacteroidales, appeared to increase in
abundance in those animals fed forage, while propionate producers, such
as Prevotella, appeared to increase in
the concentrate-fed animals. Similar
effects have been seen in other studies.
Protozoa are comparatively large
microbes that are present in the rumen at a concentration of ~105cells/
ml. They play a key role in providing nutrients for a host, as well as
the generation of methane. Protozoa
exhibit a high production of butyrate
and acetate, which yields hydrogen
molecules that are subsequently
taken up and converted to methane
by methanogenic archaea. Ruminal
protozoa can be sub-divided into
two groups: ciliated and flagellated.
Despite their other activities, it is
the methane production that has received the greatest interest from the
It is known that protozoa predate
bacteria within the rumen microbial
community, and this has a negative impact on microbial protein synthesis and,
subsequently, nitrogen use efficiency of
the cow. A study attempted to elucidate
which groups of protozoa were responsible for this predation to suppression
of this negative effect. Using labeled
rumen bacteria, they discovered that
Entodinium sp. were responsible for
three-fourths of the predation activity
in comparison with holotrich protozoa
Major protozoal groups in rumen
Proportion (% of total)
HEALTHY RUMEN FUNCTION
2.0 4.0 0.4 2.7
Source: Belanche et al., 2015
The relative abundance of the six major protozoal groups in rumen
of cattle and bacterial breakdown attributed to each of these
whose activity was insignificant.
Protozoa have also been implicated in the generation of conjugated
linoleic acid (CLA) and in vitro cultures of rumen bacteria, protozoa and
a mixture of both revealed that only
rumen bacteria were able to fully biohydrogenate linoleic acid to C18:0.
Although many studies exist looking at protozoal effects, and it is wellestablished that defaunation results
in a reduction in methane output and
has also been shown to improve nutrient use efficiency, far less is known
about rumen protozoal communities
and diversity compared with bacteria.
Rumen fungi affected by diet
Fungi are the largest of the rumen microbes with the longest generation time. There are six genera:
the moncentric Neocallimastix,
Piromyces, and Caecomyceas
and the polycentric Oprinomyces,
Anaeromyces, and Cyllamyces.
They are perhaps best known for
their ability to degrade fiber by burrowing into cell-wall material, rendering it more accessible to bacterial
enzymes and, ultimately, increasing
ruminal fiber. Fungi have also been
shown to partially biohydrogenate
linoleic acid to t11 C18:1.
Like rumen bacteria, fungal diversity is affected by diet.
Archaea and methane
Many archaea are methanogens
and are responsible for generating
methane from substrates, such as
hydrogen and carbon dioxide.
Compared with bacteria, rumen
archaea appear much less diverse.
However, an increase in methanogen
numbers per se does not necessarily translate into greater methane
production as rumen conditions may
affect expression of genes in methane production. There are known
associations between rumen cellulolytic bacteria and archaea, as well
as protozoa and archaea. The link
www.WATTAgNet.com ❙ July 2018