Home' NZ Dairy Farmer : May 2010 Contents The Dairyman MAY 2010 39
WE are what we eat and our ani-
mals are no different. They
receive the basic nutrients from
their grass based diets, however, this is
often lacking in vital minerals. The min-
eral content of grass varies throughout the
season and throughout the country.
Therefore, it is over to the farmer to
ensure these deficits are filled.
Applications of fertiliser can help to
increase the available minerals on most
soil types but remember that requirements
vary with geography.
Supplementary feeds will also vary in
their mineral balance. An example has
been the increased feeding of Palm
Kernel Expeller meal.
This is higher in organic copper than
most of our other feedstuffs, and farms
which have been feeding significant
amounts are finding a change in the cop-
per status of their herds (sometimes dra-
This subsequently affects the amount of
direct mineral supplementation the ani-
mals need (and can lead to toxic levels in
some cases if the "same old" supplemen-
tation methods are adhered to).
Changing farms, geographical regions,
or farm systems may also change the
requirements. A change in systems to
increase production may require increas-
ing the supplementation of certain miner-
als. Different areas of New Zealand will
have different soil availability of
minerals, and differing elements
competing for the uptake by the
The big three trace elements are
copper, selenium, cobalt.
Liver biopsies are the ideal way
of assessing copper status.
Although we can test blood samples for
copper, it is not indicative of the amount
of copper in storage. I often consider the
liver (and its copper stores) to be like a
If you want to know if there is water,
you turn on the tap (this is like measuring
blood levels -- it lets you know that there
is enough storage to maintain a flow).
But the level of water may be just above
the outflow, and it might only last another
couple of days before that flow slows to a
trickle. So if you want to know how
much water is in the tank, you look inside
(this is like taking a liver biopsy and
measuring the amount of copper stored).
Liver biopsies can be taken at the abat-
toir, but my preference is for taking them
from the animals that are staying in the
herd. The culls that go to the works are
often non-pregnant, or not performing in
the herd, so are not good representations
of the cows that will be staying on the
farm through the winter.
The liver copper levels in these cull
cows are often higher than the rest of the
herd (as non-pregnant cows do not have
the copper drain of the growing foetus),
and can lead to an inaccurate assessment
of the herd's requirements.
Selenium is another important trace
element that is often overlooked. The ref-
erence ranges from the Animal Health
Laboratories are based on what is "nor-
mal", and is not necessarily what is
required for performance.
As an example, the laboratory refer-
ence range for serum selenium is from
150-1000. Although the bottom of this
range is 150, levels below 300 have been
shown to negatively affect milk quality
(cell counts), immune function, and
increase the incidence of retained foetal
membranes post calving, there is now evi-
dence that we need higher levels to opti-
mise animal performance.
Cobalt is the base material for rumen
microbes to produce Vitamin B12. Some
areas are well known for being cobalt
deficient (the Central Plateau of the North
Island for example), fertiliser supplemen-
tation often is not enough to correct these
We can measure the current status via
In short, it is difficult (almost impossi-
ble) to advise on trace element
supplementation without knowing
the current status and planned
inputs/outputs. Every situation is
different, and what works on your
neighbours' farms is not neces-
sarily right for you. Please con-
sult with your veterinarian about
the best trace element plan for
Trace elements can make big difference
"Every situation is different,
and what works on your
neighbours' farms is not
necessarily right for you."
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