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28
APRIL 2018
Dairy Focus
www.irishfarmersmonthly.com
YOUR
HERD'S
DIET
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23/01/2018 12:27:16
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26/03/2018 09:55
After the cold spring we have experienced, grass covers and,
potentially, grass feeding values are below target. Cows are
going into 800-1,000kg per hectare covers. For a 100-cow herd
averaging 28L, this is 10kg DMI per head plus 3kg in the parlour,
leaving the herd in a DMI defi cit of 5kg, or an energy defi cit of
5UFL (unite forragere lait) per 66 megajoules. In this scenario,
withdrawing a buff er feed without assessing the covers that
are in front of the cows in one week's time can trigger a quick
decline in milk yield. It is, therefore, paramount after a diffi cult
spring to measure the covers in your paddocks right now. What
covers are cows going into in a week's time? Is there a defi cit?
What forages or high-energy concentrates are available to
bridge this small but detrimental energy gap?
FLUCTUATIONS IN MILK PROTEIN
When the cow's DMI and energy demand for maintenance plus
milk yield outstrips energy supplied to the cow, milk protein
percentage begins to slip. Biologically, what is happening within
the cow? The mammary gland uses protein produced by the
rumen microbes to produce milk protein; this process requires
glucose, or energy. If the cow's diet is not meeting her demands
or requirements, the cow's metabolism switches gear into a
catabolic state. The cow then begins to break down microbial
protein destined to become milk protein and converts it to
glucose. Indirectly, the cow now receives much-needed energy,
but the knock-on eff ect is that our milk protein results begin to
plummet. Let's be clear that dropping milk protein is partially
justifi ed because of the dilution eff ect of increasing milk
volume.
However, further investigation is required when milk protein
drops below base price, as this is highlighting an energy defi cit
in the cow that could adversely aff ect herd fertility in the
subsequent breeding season. From a fi nancial viewpoint, a 100-
cow herd averaging 25L with a milk protein of 3.15 per cent is
losing 850 per month because of a lower milk price compared
to the base.
If milk protein is low in the mid-lactation herd, consider the
following:
What is the quality of grass that the cows are grazing? A
build-up of dead material from previous grazing will adversely
impact milk proteins;
What is the DMI from grass? Are cows receiving 12-14kg DMI
from grass? If not, there is a need for supplementation in the
parlour and at the feed trough;
Are you feeding high concentrate levels in the parlour to
bridge the energy gap? Take a portion of these concentrates
out of the parlour and put them into a forage buff er mix. Cows
have longer access to this feed and it will promote better
rumen fi ll;
Are you buff er feeding with unpalatable, low dry matter
digestible silage? Pull back on 4-5kg of this forage and
replace with 1.5kg of maize meal, or introduce 1.5kg of
molasses with the silage to increase palatability and DMI if
grass covers are low;
Are alternative feeds available (eg. fodder beet, moist feeds)?
How much are the top 15 per cent yielding cows in the herd
averaging?
BODY CONDITION SCORING AND BREEDING
Regular BCS of cows is an important management tool. It
infl uences potential milk production, DMI, health and fertility
of the herd. At breeding, the ideal BCS is 2.75. To accurately
score your mid-lactation cows approaching breeding, fi rst
become familiar with the following anatomical features: the pin,
hook, thurl, short ribs, sacral and tailhead ligament. If the angle
between the pin and hook is a clear V, then the cow is BCS 3 or
less (the thurl is the middle point). Visually, a cow that is less
than BCS 2.75 has little fat covering around the pin, the pins
Milk peak
Milk yield (kg/day)

Intake peak

Dry matter intake (kg/day)


Body weight (kg/day)
Body weight g
ain




Weeks of lactation
Body weight of the calf
B
od
y
we
i
ght
l
o
s
s
Figure : Changes in milk yield, dry matter intake and body weight of cows through the stages of lactation
(National Research Council,
).