Dairy cow body temperatures are challenged by heat from the environment and digestion. Heat stress occurs when core temperature rises above 101.3°F. Higher producing cows that eat more feed produce more internal heat, making them more susceptible to heat stress. Intake is reduced when temperatures exceed 75°F and drops significantly above 86°F due to heat stress. Sprinklers over the feed bunk can help increase intake and milk production by cooling cows. Research shows combinations of sprinklers and fans placed strategically are most effective at cooling cows and maintaining intake and production during heat stress.

1. 462 July 2013
HOARD’SDAIRYMAN
Body temperature regulation in
dairy cows is constantly challenged
by a combination of environmen-
tal heat and that produced during
rumen fermentation and nutrient
metabolism. Heat stress occurs
when cows cannot dissipate enough
heat to maintain a core tempera-
ture below 101.3°F.
Internal heat production acceler-
ates at higher dry matter intakes,
therefore, your high producers are
more sensitive to heat stress. Body
temperatures elevated just 2.7°F
have been shown to result in intake
reductions of almost 13 pounds.
Midlactation drop severe
During lactation, cows start to drop
intakes as temperatures exceed 75°F,
with marked reductions above 86°F.
Air velocity and relative humidity
also need to be factored in. A thermo-
neutral zone can be assumed at 68°F
and 50 percent relative humidity.
The thermoneutral zone is the tem-
perature and moisture combination
where the cow is comfortable and her
organism does not need to resort to
mechanisms to cool or warm up the
body. When temperatures exceed
75°F, however, intake drops consid-
erably even at 50 percent relative
humidity. Intake is reduced more sig-
nificantly in higher producing cows
that consume more feed.
Intake reductions in groups of
heat-stressed cows are most severe in
midlactation while it is least severe
early on in lactation. Early-lactation
cows have the lowest intakes. How-
ever, they usually are the ones that
produce more milk. Their advantage
is that their metabolism is in “tissue
mobilization mode” and can readily
utilize body reserves to compensate
the effects of environmental heat.
Second-lactation or greater cows
that are pregnant have greater intake
reductions than pregnant first-lacta-
tion cows. When cows are subjected
to heat stress, a significant portion of
their body heat is eliminated through
the skin. As ambient temperatures
rise, however, skin losses are reduced
while panting hikes to augment heat
emission through evaporation.
Intake and production are more
closely associated with the tempera-
ture of the two previous days than
those of the present one. Whenever
necessary, it is important to have
strategies that reduce temperature
at night. Cows can tolerate higher
temperatures during the day when
ambient temperatures at night drop.
Need evaporation time
Among the most effective strate-
gies to improve intake and produc-
tion are sprinklers over the feed-
bunk. Sprinklers soaking the coat
and skin should work intermittently
to allow time for water evaporation
before the next soaking cycle.
Researchers from the University of
Missouri-Columbia placed two lines
of sprinklers in the freestall; one on
top of the feedbunk and the other in
the alley between the stalls and side-
wall. Sprinklers were set on 30-min-
ute cycles (20 on, 10 off). Although
they reduced rectal temperature by
0.5°F, they only improved yield by
1.5 pounds. Production rose by 4.4
pounds per day when the experiment
was replicated with forced air over
the feedbunk and stalls.
In an Alabama experiment, sprin-
klers over the feedbunks improved
intake and milk yield by 2.2 pounds
per day. In this experiment, sprin-
klers were on 15-minute cycles (3 on,
12 off) with fans over feedbunks and
stalls. It was determined that fans
alone did not improve cow comfort.
Both strategies need to be combined
to treat cows under severe heat stress.
Kansas State University (KSU)
research evaluated three combina-
tions of sprinklers and fans dur-
ing the summer in barns with four
rows of stalls. All treatments had
sprinklers over the feedbunk pro-
grammed in 15-minute cycles. One
treatment had two rows of fans over
the stalls, another had one row of
fans over the stalls and one over the
feedbunk, and the last treatment
had two rows of fans over the stalls
and one row over the feedbunk.
Cows cooled with fans over the
stalls and feedbunk produced more
milk than those with fans only
over the feedbunk (98.8 versus 93.9
pounds per day). There was no pro-
duction response when the number
of fans over the stalls was doubled.
Combinations work best
A subsequent experiment evalu-
ated two cooling systems, both with
sprinklers and fans over the feed-
bunk, but only one of them had a
line of fans over the stalls. It was
confirmed that, when fans over the
feedbunk were complemented with
those over the stalls, milk yield rose
by 5.7 pounds per day.
The effectiveness of the cooling
system depends on the number of
rows of stalls:
Four rows: sprinklers over the feed-
bunk and two rows of fans, one over
the stalls, one over the feed bunk.
Two rows: one row of sprinklers
over the feedbunk and one of fans
over the stalls.
Researchers at KSU compared the
capacity of soaking frequencies to
reduce body temperature in cycles
of 5, 10 and 15 minutes. Each cycle
supplied approximately 0.35 gallon
of water per headlock per minute.
Airflow was continuous at 700 cubic
feet per minute (CFM). The drop in
body temperature rose with soak-
ing frequency. The most effective
system was continuous forced air
and 5 minutes (1 on, 4 off) soaking
frequency. With this soaking fre-
quency, there were no advantages of
airflow above 750 CFM. It’s impor-
tant that cows are dry before the
next cycle starts.
According to KSU research, mis-
ters over the feedbunk coupled with
forced air can have a similar effi-
ciency to 5-minute cycle sprinklers
only when they soak the cow’s skin
completely. To achieve this they
must work with a minimum water
flow of 3.4 gallons per hour. With
high-pressure misting, there’s a
combined effect of cooling both the
surrounding air and the animal
through water evaporation.
Misters with water flows of 1.7
gallons per hour were able to drop
body temperatures in cows, but
were not as efficient as those with
3.4 gallons per hour or sprinklers
with 5-minute cycles. In addition,
continuous high-pressure misting
systems at 3.4 gallons per hour
use 18 percent less water than
sprinklers in 5-minute cycles.
A cooling program could raise
soaking frequency at the feedbunk
as ambient temperatures elevated.
Extended periods of high ambient
temperature coupled with high rela-
tive humidity compromise the ability
of the cows to dissipate excess body
heat. Supplemental fan cooling and
low pressure feedbunk sprinklers
can reduce the effects of heat stress
on milk production and intake.
Cool cows keep intakes up
Feeding
by Fernando Díaz-Royón and Álvaro García, D.V.M.
The authors are in the Dairy Science Depart-
ment, South Dakota State University, Brookings.
How often should you soak?
Ambient
temperature
Soaking cycle
frequency
Between 77°F
and 86°F
12 minutes
(1 on - 11 off)
Above 86°F 8 minutes
(1 on - 7 off)
INTAKES BEGIN TO DECLINE as temperatures exceed 75°F. This drop will be most severe for
your midlactation cows along with those in their second lactation. Sprinklers over the bunk
are one of the best methods to foster higher intakes.
Used by permission from the July 2013 issue of Hoard’s Dairyman.
Copyright 2013 by W.D. Hoard & Sons Company, Fort Atkinson, Wisconsin.