AgriBusiness News September 2017

WAIKATO AGRIBUSINESS NEWS September 2017 35
Promising research reducing
nitrogen in urine
CRV Ambreed’s genetic research into
reducing nitrogen leaching on New Zealand
dairy farms has identified that when cows
are bred for low milk urea concentration, a
proportion of the nitrogen diverted away from
the cow’s urea goes into milk protein.
This finding gives CRV
Ambreed further
confidence that breeding
cows for low milk urea
concentration will not only
reduce the amount of nitrogen
excreted in their urine, but will
also increase the efficiency with
which dietary nitrogen is used
for milk protein production.
The search to understand
precisely how animals partition
the nitrogen they consume has
been the subject of decades
of research into making cows
more efficient in the way
they use dietary protein. The
relationship between milk urea
and the percentage of protein
in milk identified by CRV
Ambreed should give scientists
new leads for that work.
The dairy herd improvement
company has begun marketing
semen from more than 20
existing, high-performing bulls
under a LowN Sires brand.
The bulls are desirable for
traditional traits as well as being
genetically superior in their
ability to reduce concentration
of Milk Urea Nitrogen (MUN)
in their daughters.
MUN is a measure of the
amount of nitrogen contained
as milk urea and there’s very
strong international evidence
of a direct connection between
MUN and the amount of
nitrogen excreted in urine when
cows are fed varying diets -
cows with low MUN excrete
less nitrogen as urine.
CRV Ambreed has shown it
is possible to breed cows that
genetically have lower MUN.
These cows are then expected
to excrete less nitrogen as
urine and consequently less
nitrogen will be leached into
groundwater. Calculations by
CRV Ambreed show a reduction
of 20 percent in leaching within
20 years is possible by using
genetics to breed cows with
lower levels of MUN.
Now, further analysis
indicates where at least some
the nitrogen goes if it’s not
going into urea. This finding
is thought to be a world-first
in demonstrating variation
between cows of differing
genotypes for how they
partition dietary nitrogen eaten
in the form of protein.
CRV Ambreed R&D
scientist Phil Beatson says
dairy cattle convert nitrogen
consumed into five areas:
milk (protein + urea); growth
(muscle); dung; gases; and
urine.
“From an environmental
perspective, we saw urine as
being the big issue because of
its impact on water quality,” Mr
Beatson says. “And we asked:
can we breed cows that have
reduced MUN, and if so do
these cows excrete less nitrogen
as urine?
“Now we know that we
can reduce MUN through
breeding, and that these low-
MUN cows will partition more
dietary nitrogen from milk
urea towards milk protein.
This strongly indicates that
low-MUN cows will excrete
less nitrogen as urine because
they divert some nitrogen away
from milk urea and into milk
protein.”
This means not only can
LowN Sires bulls and a low-
MUN approach be used to
breed for environmental gains,
but also possibly for an increase
in animal efficiency.
Mr Beatson says modelling
and genetic analysis of the
LowN Sires bulls suggests
about 25 percent of the nitrogen
that will be diverted away from
urine in their daughters will
go into milk protein. Higher
percentages of milk protein is
good news for milk processing
companies desiring less water
in the drying process.
He understands the low-
MUN and high percentage
protein genetic link is a
world-first and could therefore
be a clue to understanding
how animals partition the
nitrogen they are fed. “Animal
nutritionists will be extremely
interested in our finding as there
have been decades of research
into nitrogen-use efficiency.”
Mr Beatson says this
discovery could be the tip of the
research iceberg. “A huge effort
has been invested over the past
70 years trying to understand
nitrogen partitioning and that’s
produced some interesting
trends but nothing conclusive.
Now New Zealand scientists
may target groups of animals
that are known to be diverse for
MUN to investigate differences
in how they partition dietary
nitrogen.”
He says while breeding
versus feeding cows are
different avenues in terms of
reducing nitrogen excreted as
urine, the two are expected to
be additive. “In other words,
genetic gains will add to gains
from better feeding.”
It may also have implications
for more than dairy cows. “This
research gives us confidence
that cows bred for reduced-
MUN will partition nitrogen
differently and this is likely to
be true for all ruminants.”
Phase 2 of the research
will study groups of animals
genetically different for MUN
to understand more precisely
the relationship between
reducing MUN and reducing
nitrogen in urine.
GENETIC DISCOVERY: CRV Ambreed’s R&D Scientist Phil Beatson.
HOW LOW MUN AND LOWN
SIRES WORKS
The primary cause of nitrogen leached into the ground and
waterways comes from the cow’s urine having very high
concentration of nitrogen and being deposited in small
patches. Some of the nitrogen excreted is converted to
gas, some is taken up by plants, and a substantial amount
is leached, with soil-type affecting the proportion that is
leached.
CRV Ambreed, with the input of other researchers, has
spent five years investigating the genetics of Milk Urea
Nitrogen (MUN). The rationale has been that if it’s possible
to reduce MUN through traditional genetic selection means,
and providing the relationship between MUN and amount
of nitrogen excreted in urine holds, then the genetically
improved animals for MUN will excrete less urinary nitrogen
and hence leaching per animal and per hectare can be
reduced.
“Cows bred for lower levels of MUN are expected to excrete
less nitrogen in their urine which will, in turn, reduce the
amount of nitrogen leached when cows are grazed on
pasture,” CRV Ambreed R&D Scientist Phil Beatson says.
“It could potentially save New Zealand 10 million kilograms
in nitrogen leaching a year within 10 years, based on the
national herd number of 6.5 million dairy cattle.”
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