Download Nitrate – a possible alternate dry season

LIVESTOCK BEEF PRODUCTION
Nitrate – a possible alternate
dry season supplement?
During the dry season in northern Australia’s pastoral regions, nitrogen is often the primary limiting nutrient in the low
quality, tropical forages available to cattle. To counteract this, graziers usually supplement cattle with urea. But in recent
years, researchers have been looking at the feasibility of using nitrate salts as an alternative supplement, which reduces
methane production by animals and may offer better feed conversion efficiency than urea. By Pamela Lawson
NITROGEN NEED
Sufficient dietary nitrogen is needed for
ruminants to provide a source of ammonia
to support microbial growth and protein
production in the rumen. This process in
turn increases pasture intake and therefore
liveweight gain. Although supplementing
cattle with non-protein nitrogen (such
as urea) generally results in only small
liveweight gains, it is a common and
practical strategy to reduce production
losses during the dry season.
Cattle grazing on low quality, tropical
pastures produce high amounts of methane
during digestion. About half the methane
emissions from cattle can be attributed
to cattle in extensive grazing systems
in Queensland and Northern Territory.
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Although naturally occurring, methane
emissions represent an inefficiency in the
conversion of feed to protein and energy.
They can however be reduced by improving
the diet quality and therefore production per
animal, which in turn reduces the emissions
of methane per kilogram of animal product.
In intensive or small-scale grazing
operations, managing livestock so they
are grazing on younger pastures with
some legume content will improve diet
quality and productivity whilst reducing
methane production. But this is not
possible for the extensive grazing systems
of northern Australia without significant
capital investment and changes to current
management practices. This has prompted
the University of New England (UNE) to
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AT A GLANCE
▸▸ Recent research has flagged nitrate
as a possible alternative dry season
supplement to urea for northern
Australia beef cattle herds.
▸▸ While nitrate feeding holds similar
risks to urea supplementation, it
reduces methane emissions from cattle
significantly.
▸▸ Financial considerations and the current
lack of monetary reward for methane
abatement may limit the use of nitrate
at present.
Graziers in northern Australia typically supplement
their cattle with a non-protein nitrogen such as
urea to maintain production during the dry season.
Photo: Pamela Lawson.
No. 293 June 2016 Farming Ahead
57
lead a number of projects looking at nitrate
as a potential alternative source of nonprotein nitrogen to urea, whilst reducing
methane emissions in livestock.
FEEDING NITRATE
Most northern Australian graziers have had
experience with feeding urea supplements
during the dry season, and feeding nitrate
as a supplement is very similar. Like urea,
nitrate salts can be fed as part of a molassesbased mix, low-intake loose lick or lick
block. Feeding nitrate carries similar risks
to feeding urea, as excessive consumption
of either can cause toxicity in cattle. Once
eaten, nitrate is converted to nitrite and
then ammonia, which is used by rumen
microbes to make protein. If nitrate intake is
excessive, nitrite can accumulate faster than
it can be turned into ammonia.
This results in nitrite being absorbed
through the rumen wall into the blood,
where it reduces the ability of blood to
transport oxygen around the body and
causes poisoning.
Toxicity generally occurs when nitrate
concentrations in the diet exceed nine
grams per kilogram of dry matter. But other
variables that influence the extent of toxicity
include the rate of nitrate intake, the rate
of feed digestion (release of nitrates into
the body), the rate nitrite is converted to
ammonia and diet quality.
But UNE researchers are confident the
risks of toxicity when feeding nitrate can be
minimised by careful management. Feedlot
studies have shown feeding a given dose
of nitrate over several feeds rather than
as a single dose each day reduces the risk
of poisoning occurring, as does feeding
nitrate as part of a total mixed ration or with
pelletised grain or oaten hay. In general,
higher digestibility diets have an increased
conversion rate of nitrate to nitrite to
ammonia so toxicity is less likely to occur.
While current research suggests that nitrate
can replace urea in an extensive grazing
system with no additional risk, research
continues to determine how to best manage
risk mitigating factors.
IS IT WORTH IT?
With similar risks to feeding urea, producers
may question the benefits of feeding nitrate
over urea. In terms of production benefits,
a UNE feedlot study showed a 3% better
feed conversion efficiency from feeding
nitrate rather than urea. However similar
results have yet to be shown in an extensive
grazing situation.
There are also financial considerations
when deciding which supplement to feed, as
nitrate salts have a lower nitrogen content
than urea which means it has to be fed at
greater rates for a similar result. This is
likely to increase daily feeding costs by
58
Farming Ahead June 2016 No. 293
Supplement bar: Cattle licking nitrate blocks late in the 2014 dry season during a UNE supplement trial in
northern Queensland. Photo: Joseph Miller.
about 2.5 times compared to the current
urea-based supplement feeding regime.
The UNE researchers found feeding cattle
nitrate in an intensive system can reduce
methane emissions by 10-30%. Significantly
lower mitigation levels have been shown in
extensive grazing systems. While methane
production is normal and advantageous,
it would be far more productive for beef
producers if methane energy could instead
be converted into growth.
Reducing methane as an inefficiency in
livestock systems will also become more
important as food demand and climate
change impact government policy and
ultimately result in product prices that factor
in methane abatement. But for the time
being it is unlikely that current government
policy will adequately reward graziers
financially for reducing greenhouse gas
emissions.
FEEDING SUPPLEMENTS
Regardless of which source of non-protein
nitrogen is used to supplement livestock
during dry seasons, graziers are also faced
with the conundrum of deciding the best
supplement strategy to employ.
In extensive grazing systems, ruminants
have to have the capacity to use a wide
range of forages with changing mineral
contents and crude protein levels. It is
therefore very difficult to predict the
mineral and nutrient requirements of cattle
grazing dry pasture because of factors such
as seasonal variability and its effect on
the stage of pasture growth and the effect
of leaching on pasture crude protein and
mineral composition.
Ruminants have evolved to survive
periods of nutrient deficiencies by
developing the ability to find and try
materials to remove a metabolic discomfort
and correct the deficiency.
Individual sources of urea, sulphur,
phosphorus or even trace minerals will
be sought by grazing animals as these
substances become deficient in the available
feed. Research has shown that animals
self-medicate by selectively seeking out
materials that supply the deficient nutrient
or prevent the harmful effects of toxins in
their feed.
Examples of this include chewing bones
or the bark of certain trees, detoxifying
feeds by consuming clay minerals to bind
toxins, selecting higher protein diets when
pregnant or lactating or consuming more
of a medicated block when infected with
internal parasites.
The UNE researchers set up a free-choice
based self-medication program under an
extensive grazing system near Richmond,
Queensland. Although the trials are
continuing, early results indicate the most
effective program was to offer year-round
availability of mineral and urea/nitrate
supplements.
Essentially three separate supplements
are needed for free choice supplementation,
with a background of other minerals also
on offer. One supplement should be high
in nitrogen (usually non-protein like urea
or nitrate), one high in sulphur, and fed as
three separate lick supplements.
Under this program, the researchers found
that animals seem to be able to balance
their needs and the disappearance of blocks
signals the onset of deficiency.
UNE researchers are now using remote
pastoral management technologies such
as walk-over weighing, GPS collars and
supplement intake monitoring equipment, to
refine their findings.
By conducting station-based trial
testing the effects of urea, nitrate and free
choice mineral supplement systems on
productivity and emissions the researchers
are now hoping to quantify the variation
in individual animal grazing, supplement
intake and watering behaviour and their
affect on animal productivity.
Contact:
Joe Miller
Project Officer, Animal Nutrition UNE
0477 374 424
[email protected]
© Kondinin Group – Reproduction in whole or part is
not permitted without permission. Freecall 1800 677 761
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