North Canterbury News: September 12, 2019

RuralLife
Genetics can be used in tackling
nitrogen leaching from farms
Farmers have been challengedto
reduce the amount of nitrogenleaving
theirproperty throughsub soils and
waterways.
This has seen the adoption of more
responsiblefertiliser and effluent
management, and, more recently,work
on more efficient nitrogenuptake in
plants and animals.
One of the harder sourcestomitigate
is nitrogen leaching from cows’ urine.
The concentrationofnitrogen in the
urinepatchissohigh that asignificant
proportion cannot be usedbyplantsor
retained in the soil root zone.
While reducingurinarynitrogen
ideally involves measuring it, that is
impractical to do in large numbersof
cowsdirectly —and that is wheremilk
urea concentration (MU)comes in.
Manyinternational studies have shown
adirectrelationshipbetween MU and
the amount of urinarynitrogen per cow
per day.
It makes sensetoreduce urinary
nitrogen fromafarmingperspective
and to monitor urinary nitrogenfrom a
regulatory perspective.
One strategytoreduce urinary
nitrogen is through goodfeeding
practices and to monitortheseby
keeping an eye on milk urea
concentration,
And asecondstrategy is where CRV
Ambreed’s genetics comesin.
CRV Ambreed’s LowN Sires
programme is based on breeding dairy
cows withlowerlevelsofMU, whichis
expected to reduceurinary nitrogen.
‘‘Milk urea tells us alot. We knowwe
can reducemilk urea through feeding,
but also through genetics,’’ CRV
Ambreed headgeneticist Phil Beatson
says.
Each day farmers get aMUvalue
measuredintheirbulk milk. It makes
sensefor farmers and regulators to use
this milk ureaconcentrationtomonitor
nitrogen loading from urine. Total
The nation’s primary industries want practical solutions to incoming
restrictions on nitrate use. Tim Fulton explores one of the possibilities,
developed by genetics firm CRV Ambreed.
urinary nitrogenper herdper day can
be calculatedbased on the weighted
MU and numberofcows. The weighting
factor to convert MU to gramsofurinary
nitrogen percow per day is around
seven.
‘‘We’re suggesting MUsshouldbe
used by farmers and by the likes of the
environmentcouncils to calculate
nitrogen depositionquite accurately.
Thisislikely to be abetter monitoring
tool than usingpredictivemodelsthat
are subject to manipulation,’’ Beatson
says.
Adairy cow eatsabout 180kg of
nitrogen ayear as plant protein. About
30kg ends up as milk and alittle bit to
body maintenance and growth. Of the
remainder, about 75 to 80kg is excreted
as urinary nitrogen and the rest is
excreted as faeces.
On average,around 20% (16kg) of this
urinary nitrogenends up being leached
into groundwater.
Importantly,asmall amount of the
nitrogen in urine isconverted to
nitrous oxide ­along­lasting
greenhousegas. Reducing urinary
nitrogen is critical to reducingboth
leaching and greenhouse gas
emissions.
‘‘If we feed diets thatcontainsurplus
protein we increase nitrogen intake
beyond whatthe cow requiresand this
is reflectedinthe milk urea values for
the herds.’’
The average herdwas around30units
for bulkmilk urea.However,some
herdswere consistently around40
whileothers were around20. The
average cow in the herdwith milk urea
of 40 is peeingout around 280 grams of
nitrogen percow per day (40 x7), while
those in the herd with milk urea of 20 is
peeingout around 140 grams of
nitrogen per day (7 x20).
The CRV Ambreed genetics
programme involved measuring MUin
amillion milksamples from 200,000
cowsthrough CRV Ambreed’s herdtesting
service. These recordswere
analysed to estimate the geneticmerit
of the siresofthe cows.The best of
these siresare marketed as LowN, and
CRV Ambreed is already providing
farmers with semenfrom bulls under
its LowNSiresbrand.
The LowN Sires bulls were desirable
for traditional traitsaswell as being
genetically superiorinreducingMUin
their daughters.
Cowsbred for lower levelsofMUare
expected to excreteless nitrogen in
their urine which would, in turn,
reducethe amountofnitrogen leached.
CRV Ambreed expected LowNSires
wouldreduce nitrogenleachinginNew
Zealand by 14 million kilograms ayear,
based on the national herd number of 5
million dairycows.
The beauty of agenetics solution to
nitrogen leachingisthat farmers
simply needtouse semenfrom the
LowN bulls rather than other bulls.
Theycan maintain all existing
management practicessothere is
minimaladditional costfor them.
However, the combinationofgood
feeding plus LowNsiresgivesfarmers a
two­pronged attack to reduce MU and
nitrogen leaching.
Reducingthe national average MU
value from 30 to, say, 24, wouldreduce
urinary nitrogendeposition by 20% and
haveaneven greater impact on
nitrogen leached.
www.jj.co.nz
03 344 5645
Competition winner ...
Jacob Paulin.
PHOTO: SUPPLIED
Jacobawinner
You don’t havetocome from afarm to be a
‘‘future farmer’’.
JacobPaulin,who is theson of builder,
won the recent annual OxfordArea School
‘‘future farmer’’ competition.
‘‘If you’reinterested in agriculture I
wouldrecommend doing it. It really tests
your skills and whatyou know,but you
don’thave to be from afarm.’’
Jacob, who is in Year 11, was runner­up
last yearand says he has akeen interestin
agriculture.
‘‘I wanttogointo engineeringand maybe
laterbeafarmer, butIwant to get
something under my belt first.’’ He works
on adairy farm after schooland in the
weekends,doingfencing, tractor and stock
work,and helpingwith baling. Next year he
planstodoabuildingprogramme through
the Ara Institute of Canterbury,while also
gaining experience through Oxford Area
School’s gateway programme.
The eight finalists weretestedonstock
judging, driving atractor,testingsoil
moisture content,first aid, abeehive
module, setting up awater tankand seed
identification.
The school willhold arural day on
Friday, October 25, with the Boys’ and
Girls’ Agricultural Club pet day. Calves will
be back, along with strict protocols to
esnure there is no risk of spreading
Mycoplasmabovis.