A42—Lancaster Farming, Friday, July 3,1981
Have you prepared your cow facilities for hot
R.A.Erdman
Assistant Professor
Department of Dairy Science
University of Maryland
COLLEGE PARK, Md. - We
are again heading into the hot
summer season.
For most dairy producers, hot
weather means an annual slump in
milk production from heat stressed
cows. But proper management can
greatly reduce the loss in milk
production during hot weather if
management decisions are based
on an understanding of how cattle
maintain body temperature.
Body temperature is a function
of the amount of beat generated in
the animal plus that gained from
the environment, minus the
amount lost to the environment.
When the amount of heat
generated in the body is greater
than that lost, body temperature
rises.
Since body temperature
plays such an important part in the
animal’s metabolism, slight
temperature increases or
decreases can drastically effect
milk yield of dairy cows.
Rarely is outside temperature
greater than the animals’s body
temperature (101.5°F) and thus
heat generally moves from the
animal to its environment. In
ternal sources of heat include that
generated from rumen fer
mentation and heat generated
from such functions as breathing,
blood circulation and exercise.
The problem in hot weather is
that cows produce excess heat, and
it is difficult to dissipate.
The animal loses heat prin
cipally by three means.
The first, radiation, is simply the
natural tendency of heat to move
from a high to a low temperature.
Obviously, this heat exchange
works both ways. Animals in the
sun tend to absorb radiant heat
similar to a dark roof on a building.
In contrast, the cow in shade
radiates heat. This illustrates the
importance of providing shade to
cattle in hot weather.
A second means of losing heat is
by convection or air circulation.
Finally, the most important way
which a cow loses heat is by
evaporation; for example, through
sweating and respiration. Un
fortunately the efficiency of
evaporation is greatly reduced in
humid weather.
Now, the question is how can
the dairy producer manage cows to
alleviate heat stress?
First, provide plenty of cool
fresh water. Water at 50 degrees
Fahrenheit can absorb almost 20
percent of the total heat that a cow
produces. And of course, cows
need water to cool themselves via
evaporation.
Not only is availability of water
important but so is its location. If
cows spend all day a half mile from
the water source, it is unlikely that
they will consume as much water
as they need. Dairy producers
should minimize movement of
cattle in hot weather. Remember
exercise generates heat which the
cow must work to get rid of.
Consider some options in this
regard. It is really necessary to
move cattle to a distant pasture
during hot weather? Consider time
of day when cows are moving. Try
to do this during the coolest part of
the day.
Types of feed and feed
management are also very im
portant. Research shows that in
hot weather, cattle consume 70
percent of their total feed in the
evening hours.
Do you typically fill the feed
bunk in the evening to last only 2-3
hours? If so, you may be lowering
your cows’ feed consumption
which is the chief reason for
lowered milk production in hot
weather. So always try to feed the
cows during the coolest parts of the
day.
Cows also have a natural ten
dency to eat less forage in hot
weather because rumen fer
mentation of forage produces more
heat than fermentation of con
centrates. To compensate for this
dairy producers should feed more
grain in hot weather to maintain
energy intake. However, this
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- aggravates problems with lower
milk fat tests which are more
prevalent in the summer.
It may be wise to add a buffer
such as sodium bicarbonate at the
rate of 30 pounds per ton of con
centrate. An increase of .1 to .2
milk fat percent will pay for the
added cost of the buffer.
It may also pay to feed more
often in the summer to keep feed
fresh. Remember silage decays in
the feed bunk; and the wanner the
weather, the faster the rate of
spoilage.
What are other steps that the
dairy producer can take?
Consider how your cows are
housed. If they are in confinement,
is the air circulated adequately?
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weather?
Remember anything that impairs
air movement greatly reduces
dissipation of heat via convection.
Ridge openings and fans should be
considered.
For animals in stall barns,
minimum fan capacity is at least
15 air changes per hour. Consider
the use of large fans to blow air
directly through buildings.
For dairy producers that keep
their cattle outside, is shade
available? If not, consider keeping
them in during the day and turning
them out at night.
Although all of these steps may
involve more work or a change in
normal routine, the benefits in
improved production from proper
management during hot weather
will almost always pay for the
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