Agriculture Reference
In-Depth Information
hydrogen competitor or CH 4 oxidative pathway
could reduce CH 4 production. For example, ace-
togens can also utilize hydrogen as substrate and
have been found to be dominant in kangaroos'
rumen. If acetogens that can outcompete metha-
nogens in hydrogen intake are selected by geneti-
cally modifi ed technology and then form stable
microfl ora in rumen, less CH 4 would be produced
from ruminants. CH 4 oxidation may be another
possible solution to solve this problem.
Methanotrophic bacteria can oxidize CH 4 to car-
bon dioxide, and they inhabit widely diverse
environments. Through genetic modifi cation,
bacteria with high CH 4 -oxidative effi ciency can
be obtained. Once these bacteria are introduced
into rumen and form stable microfl ora, CH 4 will
be used to form carbon dioxide without affecting
ruminal fermentation.
At present, the researchers worldwide engag-
ing in CH 4 emission mitigation of ruminants
mainly focus on nutrition regulation, optimiza-
tion of feed formula, and application of additives.
In comparison, the CH 4 mitigation in ruminants
using genetic modifi cation is only just now being
investigated. This technology, marked by com-
plexity of operation, excessively high up-front
investment, and long period of study, requires
multidisciplinary cooperation. All these factors
together restrict the development of genetic mod-
ifi cation of microorganisms to reduce CH 4
emissions.
once the genetically modifi ed microbes sur-
vive in rumen, they will be carried by rumi-
nants as long as they live and can be inherited
by their offspring, without any extra costs to
maintain CH 4 mitigation.
• Although chemical inhibitors or antibiotics
can reduce CH 4 synthesis, the long-term adop-
tion may cause residues of organic matter or
antibiotics in meat and milk and bad health
conditions of animals. However, genetic mod-
ifi cation of microorganisms in rumen can
eliminate all the adverse effects mentioned
above and achieve CH 4 emission reduction on
the premise that food security is guaranteed.
13.2.2.2 Disadvantages
In spite of the advantages of genetic modifi cation
of rumen microorganisms in reducing CH 4 emis-
sions in rumen, several problems and technical
barriers remain.
• Most of the microorganisms in rumen are hard
to isolate or culture. Mutagenic screening and
genetic modifi cation require more information
on the mechanism and ecological functions of
microbial metabolism and are still at a trial
stage.
• Relevant reports indicate that technical barri-
ers exist for introducing genetically modifi ed
strains into the rumen ecosystem, as well as
for establishing a stable microfl ora and a sta-
ble symbiotic relationship (Cotta et al. 1997 ).
Genetic modifi cation of rumen organisms is a
system engineering problem involving nutrition,
molecular biology, physiology, genetics, micro-
biology, biological chemistry, and so on. Though
this fi eld has just started, the perspective of CH 4
mitigation in ruminants has been highlighted by
this technology. Since the research on genetic
modifi cation of rumen microorganisms is based
on the principles of genetics, this modifi cation is,
in theory, supposed to be inheritable, which is the
greatest advantage of this technology. Once this
technology can be put into actual application,
ruminants will not only reduce CH 4 emissions
but also be capable of passing their ability in CH 4
reduction to their offspring, permanently.
Compared to others, this technology could
change the rumen CH 4 problem once and for all,
13.2.2.1 Advantages
• Improving digestibility, fermentation, energy
utilization effi ciency of feed, and animal
performance.
• Methanogens and other microorganisms form
symbiotic relationships and benefi t mutually
(Joblin et al. 1989 ), so introducing genetically
modifi ed microbes favors the homeostasis of
microbial diversity and complexity of symbi-
otic relationship in rumen, avoiding side
effects on rumen ecosystems.
Many approaches for reducing CH 4 emissions
have been tried, including research on feed
preparation, vaccines, and additives (Yvette
et al. 2009 ). However, these approaches lack
sustainability and heritability. In comparison,
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