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Buckeye
Dairy News
Managing
Dairy Cows During Heat Stress
Rory
Lewandowski, Extension Educator Wayne County, OSU Extension
From
Sam Custer, OSU Extention, Darke County
I
like summer. I enjoy those sunny, 80oF plus days. A dairy cow has a
completely different perspective. Most of our dairy cows prefer
cooler temperatures. At a temperature-humidity index (THI) of 68, a
dairy cow will begin to show a decrease in milk production as a
result of mild heat stress. This THI of 68 can be reached with an
air temperature of 72oF and 45% humidity, 75oF and 20% humidity, or
80oF and 0% humidity. Researchers at the University of Arizona
have found that cows with high milk production may be even more
sensitive to heat stress. This is due to the fact that a cow’s
metabolic heat output is increased as milk production increases. In
a paper entitled “Quantifying Heat Stress and Its Impact on
Metabolism and Performance”, the authors state that “…milk
yield losses become significant when minimum THI on any given day is
65 or greater.” Their research showed that when the minimum THI
was between 65 and 73, milk yield loss was almost 5 lb/cow/day.
Beyond
the decrease in milk production, there are other detrimental impacts
of heat stress on dairy cattle. According to an article posted on
the eXtension dairy web site (http://www.extension.org/dairy_cattle),
decreased rates of estrus expression, conception, and early embryo
survival can be documented at THI levels as low as 55 to 60. Dairy
cows that are heat stressed spend more time standing as compared to
cows that are not experiencing heat stress. Increased standing time
means less time lying down, which negatively impacts milk production,
and in addition, there is speculation that increased standing time
may contribute to higher incidences of lameness. When dairy cows
experience heat stress during their dry period, fetal growth can be
reduced and milk production in the next lactation can be decreased by
1000 to 2000 lb.
There
are management practices that can help to reduce heat stress for
dairy cattle and minimize the detrimental effects of heat stress. Some
of those practices include:
Provide
shade.
Increase
ventilation and cool the surrounding air through the use of fans or a
combination of fans and sprinklers. Sprinklers should be used as
humidity levels increase. Sprinkler nozzles should deliver 0.5
gal/minute at 20 to 40 psi pressure. The goal is to wet the hair
coat of the cows without water running down to and draining off the
udder.
According
to a Virginia Tech publication, fans should be spaced 30 feet apart
for a 36 inch fan and 40 feet apart for a 48 inch fan. Fans should
be at a 12 foot height and positioned at a 20 degree angle.
Keep
time in the holding pen to a minimum for cows before they enter the
milking parlor and include fans and sprinklers in the holding pen.
Make
sure the ration includes high quality forages that can help to
decrease the heat of fermentation. Take a look at the mineral
content of the ration; it may need to be adjusted to compensate for
sweating that occurs when cows are heat stressed. There may be other
products, such as yeast cultures, that could be added to the ration
that may benefit cows under heat stress, especially high producing
cows in early lactation.
More
information about these practices is available in the eXtension
article entitled “Dairy Feeding and Management Considerations
During Heat Stress” that is available on line at:
http://go.osu.edu/managedairyheatstress.
The
overall impact of heat stress on a dairy cow is determined not only
by the THI but also the duration of the heat stress. Summer brings
us extended periods of warm (some would say hot!) temperatures and
increasing humidity. Make sure you have a strategy to manage heat
stress for your dairy cows.
Read
other articles at Buckeye Dairy News
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