Agriculture Reference
In-Depth Information
1995; Czerkawski
et al
., 1966; Mbanzamihigo
et al
., 1996; McCrabb
et al
., 1997; Mathison
et al
., 1998; Hegarty, 1999a, b; Joblin, 1999;
Klieve and Hegarty, 1999; Machmüller and Kreuzer,
1999; Anderson
et al
., 2003; Machmüller
et al
.,
2003a, b; Wright
et al
., 2004a; Denman
et al
.,
2007; Attwood and McSweeney, 2008;
Mitsumori and Sun, 2008; Williams
et al
., 2008).
Currently, the unique features of rumen metha-
nogens are being characterized using compara-
tive genomics, and this new information is
providing researchers with a host of options for
anti-methanogen strategies (Leahy
et al
., 2010).
Productivity may also be enhanced through
the use of production enhancing agents such as
bovine somatotropin and anabolic steroids, for
which emission reductions up to 9% have been
demonstrated (Johnson
et al
., 1992). Because of
the growing concern over the use of antibiotics
and chemicals in animals used for human con-
sumption, the ideal mitigation strategies will
have to be safe, leave no residues in meat and
milk, be cost effective, practical, applicable
to grazing animals and suitable for on-farm
application. However, if sustained reductions in
methane emissions do not lead to increased milk
and meat production through improved animal
performance, then adoption or acceptance of
these strategies will be non-existent. Thus,
incentives or support may be needed to encour-
age the uptake of methane-reduction strategies.
Fig. 16.2.
A photomicrograph of
Isotricha
prostoma
(160 × 90
m) and the smaller
Dasytricha ruminantium
(58 × 27
μ
μ
m).
appear to pass as rapidly to the small intestine.
Rumen ciliates also consume bacterial protein
that could otherwise be used by the animal and
are only able to convert about 50% of bacterial
nitrogen to protozoal protein (Coleman, 1975).
In addition, the larger ciliates consume smaller
ciliates. As a result, the total microbial protein
flow to the small intestine is generally reduced
and excess rumen ammonia is increased in fau-
nated animals (Bird and Leng, 1978).
Methane Reduction Strategies
Dietary composition
For intensive agriculture to become a sustainable
industry with minimal environmental impact,
understanding rumen microbial ecology is
critically important. For many years, research-
ers have tried to manipulate the numbers or
activity of the rumen methanogens in order to
improve the efficiency of ruminant production
in an ecologically sustainable way. A number of
mitigation strategies for decreasing enteric
methane emissions from grazing ruminants
have been suggested, such as dietary composi-
tion, increasing the synthesis of propionate and
long chain fatty acids in the rumen to minimize
methane production, defaunating agents, mon-
onesin, propionate enhancers, nitrocompounds,
ionophores, halogenated methane analogues,
genomics, biological control and immunization,
to name just a few (Van Nevel and Demeyer,
A relationship exists between nutritional status,
productivity and methane emissions (Leng,
1992). The amount of methane generated in the
rumen is influenced by dietary factors. Assuming
reasonable feed quality, feed intake by itself has
a major impact on methane production. Simply
stated, increasing the nutritional quality of
forages is one way of lowering methane emis-
sions, as animals grazing high-quality (i.e. high
organic matter digestibility) pastures will pro-
duce the least amount of methane per unit of
intake. A higher-quality diet increases intake
and the rate of live weight gain, therefore
decreasing the amount of methane emitted per
unit of production (i.e. weight gain or milk pro-
duction), despite the fact that methane emitted
