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S P E C I A L F E A T U R E
M
y last few months here in New Zealand have been fairly quiet as the majority
of cows are dry from mid-May to mid-July. Whilst cows are dry usually they are
grazed off the farm on someone else's land. We call these people ‘graziers’
and they also are often responsible for checking the cows on a daily basis and
measuring out the breaks of feed. This allows the sharemilkers and managers a proper
break before the spring rush with time to get on top of repair and maintenance jobs.
My husband and I have certainly made the most of the time, spending every weekend
either hiking in the southern alps or skiing on the local mountain!
Winter in NewZealand
(or The New Zealand Dry Period?)
Timing of dry-off depends mainly on grass
growth or lack of it! This year we had a lot
of rain, non-stop for several days, at the end
of May which forced quite a few people to
dry off early despite the dirty conditions.
Following dry off, many cows are wintered
on forage crops plus/minus silage, hay
and straw. Forage brassica, such as kale,
is most commonly used. People really like
it because it produces a very large tonnage
of dry matter per unit area (12tDM/ha)
which means almost three times the number
of cows can be grazed on one area
compared with pasture. In Canterbury this
is especially important as there is such a
high concentration of cows in one area.
Brassicas are also liked because they
keep well into the winter without losing any
quality or quantity. Despite these advantages,
unfortunately feeding brassicas isn't without
problems. Feeding can result in rumen
acidosis, bloat, nitrate toxicity and trace
element imbalances, to name just a few.
Brassicas are high in sugar and low in fibre,
which leaves animals eating them susceptible
to rumen acidosis. You have probably seen
acidosis in cows fed on high grain diets,
some will do poorly and some have
diarrhoea. It can also result in gaseous bloat
much like we see in cattle that have gorged
themselves on grain. Feeding frosted crop
seems to be especially high risk so we
encourage farmers to wait until midday,
when things have warmed up, before
feeding a new break. Feeding a fibre source
such as straw alongside also helps. Many
brassica species also develop high levels of
nitrates. Poisoned cows are usually found
dead or are weak and have extremely
laboured breathing because the nitrate
effectively causes the animals’ blood cells to
be starved of oxygen. Most farmers will
nitrate test before a new break is fed which
can reduce the chance of a problem
occurring. Other problems we see when
feeding brassicas are Rape & Kale
poisoning (red water) and Choke.
All the risks associated with feeding
brassicas can be reduced with a few simple
rules. They never should be fed as 100%
of the diet, and they should be introduced
slowly as the cows are dried off. It is usually
fed as a break, so by making sure cows
are full already when given a new break
can reduce the chances of bloat and nitrate
toxicity. Transition cows (3 weeks off calving)
should not be fed brassicas. They have
very high calcium content and are low in
phosphorus and magnesium, and as such
many milk fevers will arise if this is done. Plus
it does not mimic their lactating diet at all.
Amy Avery
Endell Veterinary Group
23
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