Agriculture Reference
In-Depth Information
per day from fermentation of a given amount of
feed increases slightly as digestibility increases
(Hegarty, 1999b). Conversely, a poor-quality
feed produces more enteric methane. Although
these are very basic influences, feed intake and
quality do affect microbial communities in the
rumen, and although not well understood,
advancements in this area could lead to greater
reductions in the future.
The components of the ruminant diet are
important for methane production as they are
able to influence the rumen pH and subse-
quently alter the microbiota present (Johnson
and Johnson, 1995). The digestibility of cellu-
lose and hemicellulose is strongly related to
methane production. In a study by Holter and
Young (1992), a positive relationship was found
between digestibility of hemicellulose and meth-
ane output in forage fed non-lactating cows.
However, a negative relationship was found
between digestibility of cellulose and methane
output (Holter and Young, 1992). The relation-
ship between methane production and percent-
age of concentrate in the diet is curvilinear, with
methane losses of 6-7% of gross energy being
constant at 30-40% concentrate levels in the
diet and then decreasing to 2-3% of gross energy
with a concentrate proportion of 80-90%
(Sauvant and Giger-Reverdin, 2007).
The starch component of the diet is also
known to promote propionate formation,
through a shift to amylolytic bacteria and a
reduction in rumen pH, leading to a decrease in
methanogenesis (Van Kessel and Russell, 1996).
Grinding forage feed before it is ingested by the
cows also seems to decrease the production of
methane, presumably by increasing the rate of
digestion and flow through the gastrointestinal
tract, thereby limiting the time available for
methane to be produced within the rumen
(Johnson and Johnson, 1995). It is important to
note that increasing the amount of rapidly fer-
mentable carbohydrates in a diet can increase
the rate of passage from the rumen, as well as
lower rumen pH.
increase protein outflow to the small intestine
and therefore animal production (Bird and Leng,
1984; Jouany
et al
., 1988; Williams and Coleman,
1992). In previous studies, defaunation of the
rumen in sheep has produced 7-53% more wool
growth under a range of dietary conditions,
such as pasture, cereal chaff or straws with pro-
tein and sugar supplements, and silage (Bird
et al
., 1979, 1994; Bird and Leng, 1983, 1984;
Fenn and Leng, 1989; Forster and Leng, 1989a, b;
Habib
et al
., 1989; Ivan
et al
., 1992; Hegarty
et al
., 2000).
It has been estimated that methanogens
associated protozoa, both intracellularly and
extracellularly, are responsible for 9-37% of
the methane production in the rumen (Finlay
et al
., 1994; Newbold
et al
., 1995; Machmüller
et al
., 2003b). For this reason, treatments that
decrease the protozoal population of the rumen
may also decrease the protozoa-associated
methanogen population and therefore decrease
the methane production within the rumen.
Treatments normally used to defaunate the
rumen include copper sulfate, acids, surface-
active chemicals, triazine, lipids, tannins, iono-
phores and saponins (Hook
et al
., 2010).
However, maintenance of defaunated animals
can be difficult.
Organic acids
Fumaric acid is a trans-butenedioic acid widely
found in nature. Unfortunately, the
in vivo
effects of fumaric acid on methane abatement
were found to be inconsistent. In one study
(Wood
et al
., 2009), 100 g kg
-1
fumaric acid
was offered to growing lambs, resulting in a
62-76% reduction in methane output. However,
when it was fed to growing beef cattle, steers
and wethers, it did not significantly decrease
methane emissions.
Malic acid is a dicarboxylic acid, which is
made by all living organisms, contributes to the
pleasantly sour taste of fruits and is used as a
food additive. When beef heifers were fed diets
supplemented with 3.75% and 7.5% malic acid
on a dry matter basis, methane was decreased
3% and 9%, respectively (Foley
et al
., 2009).
Although it appears that organic acids may
provide some beneficial effects for methane
Defaunation
Defaunation, the removal of ciliated protozoa
from the rumen, has been examined as a way to
