Climate Change Mitigation - Climate Resilient Agriculture for Ensuring Food Security - page 312

contributor of methane emissions, accounting for
72 % in 2008. Dairy cattle accounted for 23 % in
2008, with the remainder of emissions arising
from horses, sheep, swine, and goats (EPA 2010 ).
Clearly, livestock are important sources of
methane. In fact, the US EPA calculated that live-
stock, especially ruminants such as cattle and
sheep, account for approximately one-third of
global anthropogenic emissions of CH 4 (US EPA
2006 ). Enteric CH 4 emissions from livestock are
estimated to be the second largest source of
global agricultural non-CO 2 (IPCC 2007a , b , c ).
In addition, N 2 O emissions are generated by live-
stock through secretion of nitrogen through the
urine and feces. As such, it is important to address
CH 4 emissions from livestock.

acetic acid fermentation is the dominant fermen-
tation type in rumen with a large amount of
hydrogen produced. As a consequence, partial
pressure of hydrogen increases, which stimulates
the massive proliferation of methanogens, with
an increase in methane emissions. When soluble
carbohydrates or starch are fed, i.e., the propor-
tion of dietary concentrate increases, then rumen
pH values decline, thereby inhibiting the propa-
gation of methanogens and ciliates, while increas-
ing propionic acid production (Demeyer 1967 ).
Since propionic acid fermentation consumes
hydrogen, which reduces the raw materials
needed for CH 4 formation, CH 4 emissions are
lowered. An appropriate increase of the propor-
tion of concentrate in the ruminant animals' diet
can increase the proportion of propionic acid in
rumen, while reducing the content of acetic acid,
and improving feed utilization effi ciency and
production performance of animals. Propionic
acid is mainly converted into body composition
by the liver, and then it provides energy for breed-
ing, growth, milk production, and meat produc-
tion. CH 4 emissions and propionic acid production
are negatively correlated (Church 1988 ). Hence,
controlling the concentrate and forage ration can
not only reduce the amount of CH 4 emitted but
also improves the production performance of
ruminant animals.
There are constraints in promoting CH 4 emis-
sion reductions by changing the proportion of
fi ne feed to forage feed in daily diet. First, the
concentrate to forage ratio in daily diet refers to
the proportion of the dry matter contained, and
the actual feed intake of animals may not be
consistent with the calculated proportion.
Secondly, cornstalks are not palatable to ani-
mals, so the ammonia treatment or silage pro-
cess is necessary, and there should be a process
of adoption. Thirdly, CH 4 emissions may
increase if the proportion of dietary concentrate
is out of suitable range (40-50 %) (Sun et al.
2008 ). Furthermore, farm management sees no
direct benefi ts in CH 4 reduction. There is there-
fore a need to explore new fi nancial mechanisms
under climate conventions to encourage the
application of feed optimization for reducing
the CH 4 emissions.

13.2.1 Feed Optimization

The amount of CH 4 emissions is mainly affected
by the feed type, feed intake, ambient tempera-
ture, rate of consumption of feed, balance of
nutrients in the feed for microbial growth, and
balance of microorganisms that develop (bacte-
ria, protozoa, and fungi) which largely depend on
the chemical composition of diet (Ding 2007 ).
The diet of ruminant animals (mainly cattle,
sheep, buffalo, camels, etc.) is primarily made
up of forage and concentrate. Forage mainly
refers to grass or hay with crude fi ber content
over 18 %, most commonly including corn straw,
alfalfa, and silage. Forage provides the animals
with crude fi ber, which plays an essential role in
maintaining normal rumen fermentation, provid-
ing body energy and sustaining normal micro-
bial fl ora, as well as promoting the synthesis of
milk fat by the milk cow. At the same time,
concentrates mainly supply the animals with
protein, fat, minerals, and vitamins. Therefore,
both forage and concentrate are necessary for
ruminant animals. Moreover, the ratio of con-
centrate to forage in diet will substantially affect
the ruminant animal's growth performance,
rumen's fermentation function, methane emis-
sion, and health condition.
Generally, when the proportion of forage feed
is larger, the cellulolytic bacteria proliferate, and