Agriculture Reference
In-Depth Information
abatement, further studies are needed to deter-
mine the optimal conditions for use and if the
benefits are lasting.
investigated both
in vitro
and
in vivo
for their
effects on methanogenesis (Hook
et al
., 2011).
There are many factors that may account for the
varying effect of lipids on methane abatement,
such as the ruminant species, experimental diet
and the type of lipid used. By incorporating
lipids in the feed, methane production is
decreased, either by inhibiting the protozoa, or
by increasing the production of propionic acid
(Johnson and Johnson, 1995). Interestingly,
Czerkawski
et al
. (1966) demonstrated that oleic
acid (C18:1), linoleic acid (C18:2) and linolenic
acid (C18:3), when individually infused into the
rumen of sheep, decreased methane generation
by 27%, 26% and 34%, respectively.
Fatty acids are thought to directly inhibit
methanogens by binding to the cell membrane
and interrupting membrane transport (Dohme
et al
., 2001), whereas unsaturated fatty acids
may be used as hydrogen acceptors as an alter-
native to the reduction of carbon dioxide
(Johnson and Johnson, 1995). This has led to a
number of fatty acids being investigated
in vivo
for methane suppressing effects. Myristic acid
was found to decrease methane by 22% in sheep
fed a forage-based diet, by 58% in a concentrate-
based diet when 50 mg kg
-1
dry matter was used
(Machmüller
et al
., 2003a) and by 36% meth-
ane (Odongo
et al
., 2007b) in dairy cattle fed a
total mixed ration with 5% myristic acid supple-
mentation on a dry matter basis. Moreover,
in vitro
studies have found that fatty acids, used
in combination, have the greatest suppression
of methanogenesis due to a synergistic effect
(Dohme
et al
., 2001; Soliva
et al
., 2004).
Therefore, it is likely that oil supplementation
would provide a more dramatic depression of
methane production than individual fatty acids
(Soliva
et al
., 2004).
Soy oil, sunflower oil and palm kernel
decreased methane production by 39%, 11.5-
22.0% and 34%, respectively (Dohme
et al
., 2000;
McGinn
et al
., 2004; Jordan
et al
., 2006b;
Beauchemin
et al
., 2007a). However, coconut oil
is the most popular oil for methane abatement
(Hook
et al
., 2011) and has been reported to
decrease methane from 13% to 73%, depending
on the inclusion level, diet and ruminant spe-
cies used (Machmüller and Kreuzer, 1999;
Machmüller
et al
., 2000; Jordan
et al
., 2006b).
However,
in vivo
studies involving oil supplemen-
tation are often accompanied by a reduction in
Monensin
Monensin is a polyether antibiotic, which is
banned in the EU, but widely used in North
America to increase feed efficiency, weight gain
and milk production (Hook
et al
., 2010).
Monensin inhibits Gram-positive microorgan-
isms and selects for Gram-negative microorgan-
isms, which causes a shift towards propionate
production in the rumen (Bergen and Bates,
1984; Russell and Strobel, 1989). It is believed
that monensin indirectly decreases methane
production by inhibiting the growth of the bac-
teria and protozoa (Bergen and Bates, 1984;
Russell and Strobel, 1989).
Methane abatement from monensin sup-
plementation is highly variable, ranging up to
25% with different outcomes for the duration of
these effects (Hook
et al
., 2010). It is believed
that adaptation of the rumen microbiome to
monensin may occur, thereby decreasing subse-
quent treatments of the antibiotic. In a study by
Guan
et al
. (2006), steers were fed either a low-
concentrate diet or a high-concentrate diet while
supplemented with monensin. Methane output
and rumen ciliate densities were decreased 27%
and 77% respectively, over the initial 4 weeks on
the low-concentrate diet; and 30% reduction in
methane output and 83% reduction in the cili-
ate protozoal population over the intial 2 weeks
on the high-concentrate diet. However, both
methane levels and protozoal numbers returned
to baseline within 4-6 weeks, probably because
the rumen ciliate population adapted to monen-
sin and returned to pre-treatment levels (Guan
et al
., 2006). Although monensin has been shown
effectively to reduce methane output in rumi-
nants, there are differences in the degree of
abatement depending on the diet and animal
used (Odongo
et al
., 2007a).
Lipids
Lipids, such as fatty acids and oils, are options
for feed supplementation that have been
