Heat Stress in Feedlot Cattle

Heat Stress in Feedlot Cattle
Introduction
Heat stress is a recurring issue for most areas where cattle
feeding occurs. Proper planning can provide effective
mitigation strategies and minimize death loss during
heat events.
When temperatures heat up during the summer, cattle
feeders need to assess and manage the heat stress that
their feedlot cattle may experience. Unlike pastured cattle
that have the ability to seek shade and water and air
movement to cool themselves, feedlot cattle experience
radiant heat from dirt or concrete surfaces. To reduce
the risk to feedlot cattle, feedlot operators should have
a plan for performance loss due to decreased efficiency
and feed intake, in addition to a plan to prevent death
due to heat. At temperatures above 80° F cattle endure
physiologic stress abating their heat load. Although cattle
at this temperature are not at risk of dying, they will have
an increased maintenance requirement to cope with the
heat. Typically, pastured cattle are not as susceptible to
heat stress as feedlot cattle, so this type of planning is not
required for pastured cattle.
Compared to other animals, cattle cannot dissipate
their heat load very effectively at high temperatures.
Initially, cattle rely on sweating as their primary method
to maintain core body temperatures. However, at high
temperatures (>90° F) accompanied by solar radiation,
their large body surface area begins accumulating more
heat than can be dispersed by perspiration. At this point,
cattle switch to respiration (panting) to cool themselves.
Peripheral circulation is restricted and cattle will show
evidence of heat stress.
Because cattle do not dissipate heat effectively, they
accumulate a heat load during the day and dissipate heat
at night when it is cooler. During extreme weather
conditions, when sufficient cooling doesn’t occur during

the night, cattle will accumulate heat that they cannot
disperse. Therefore, a temperature-humidity index (THI)
alone may not predict cattle heat stress because it does not
account for accumulated heat load. Another short fall of
THI is that it does not account for solar radiation and
wind speed which can also affect heat load of cattle. The
USDA Agricultural Research Service (USDA-ARS) and
the National Oceanic & Atmospheric Administration
(NOAA) have developed a heat stress forecast map,
including temperature, humidity, wind speed, and cloud
cover to more accurately predict heat stress for cattle. The
USDA-ARS and NOAA heat stress forecast is available at
www.ars.usda.gov/plains-area/clay-center-ne/marc/docs/
heat-stress/main/.
Producers should evaluate feedlot cattle daily, especially
during July and August, for evidence of heat stress.
Special attention should be paid to cattle with increased
risk of heat stress including heavy cattle, black or darkhided cattle, and respiratory-compromised animals.
Heavy cattle cannot handle heat stress as well as lighter
weight cattle; increased fat deposition prevent cattle
from regulating their heat effectively. Solar radiation is a
critical component that can lead to death loss from heat
stress. Typically, more black-hided cattle die during heat
waves than cattle that are lighter colored. Since cattle rely
on respiration as a method to manage heat, respiratory
function is important. Cattle that had severe respiratory
disease early in the feeding period will have decreased
ability to regulate their heat load.

Recognizing Heat Stress
As the heat load increases, cattle will display increased
levels of heat stress. Initial indicators of heat stress (stage
1) include a slightly elevated breathing rate, restless
attitude, and increased time standing. During stage 2 the
respiratory rate will remain increased and cattle may begin
to drool. Most of the animals will be standing and restless,
PMR 1016 Revised June 2018

Managing Heat Stress

and cattle may begin to group together. As heat-stressed
cattle move into stage 3, respiratory rates will increase
and excessive drooling and/or foaming will be evident
(Figure 1). At stage 4 of heat stress open mouth breathing
begins and drooling decreases. Cattle in stage 5 of heat
stress will have increased respiratory effort including an
abdominal effort and protruding of the tongue (Figure 2).
The final stage of heat stress (stage 6) includes labored
breathing with the head down; severely affected animals
will isolate themselves from the herd. Calves in stages 5
and 6 are at increased risk of death from heat stress if they
do not receive relief. Calves should be cooled down slowly
by spraying with cool water and providing shade. Do
not stress calves by trying to move or restrain. Although
cooled some calves may die from organ failure days later
after recovering from the initial heat stress.

The water requirement for cattle increases during heat
stress as cattle lose water from increased respiration and
perspiration. Water consumption is the quickest method
for cattle to reduce their core body temperature. During
times of heat stress, water consumption will be greater
than times of typical metabolic requirements. Access to
adequate water sources is critical to managing heat stress
and water resources must be carefully managed. The rule
of thumb is that cattle need three inches of linear water
space per head during the summer. If existing water tanks
are not enough, extra water tanks should be introduced
prior to extreme heat events so that cattle become
accustomed to them. It is important to allow for extra
water space because some cattle will dominate a single
tank and prevent other cattle access to this critical resource
(Figure 3). Rate of water delivery is also important. The
water supply should be able to deliver 1.1 percent of body
weight of the cattle per hour. A 1,000 pound animal needs
about 1.5 gallons of water per hour. In addition, water
tanks need to be kept clean to encourage cattle to consume
adequate water.
Heat production from feed intake peaks four to six hours
after feeding. Therefore, heat production in cattle fed
in the morning will peak in the middle of the day when
environmental temperatures are also elevated. To alleviate
some of the heat load from feed, cattle should receive
a least 70 precent of their feed in the late afternoon
or evening, two to four hours after peak ambient
temperature. Ration modifications may also be needed.
Changing the ration has been controversial, but research
indicates that lowering the energy content of the diet will
decrease the heat load. The general recommendation is
to reduce the diet energy content by five to seven percent
during high temperatures.

Figure 1. Stage 3 heat stress. Photo courtesy of G. Dewell.

Working cattle will also elevate their body temperature.
For this reason, cattle should not be worked at all during
times of extreme heat. They should only be worked in
the early morning when it is going to be hot. Nor should
cattle should wait in processing areas longer than 30
minutes when it is hot. During a heat event, when the
heat index is between 90 and 100 degrees, do not work
cattle in the evening, even if it has cooled off. Cattle’s core
temperature peaks two hours after the peak environmental
temperature. And it takes at least six hours for cattle
Figure 2. Stage 5 heat stress. Photo courtesy of G. Dewell.

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to dissipate their heat load. Therefore, if the day’s peak
temperature occurred at 4:00 p.m. cattle will not have
recovered from that heat load until after 12:00 a.m.
(midnight) and it will be later than that before cattle
have fully recovered from the entire day’s heat load.

earthen mounds will also allow cattle more exposure to air
movement. Feedlot managers should assess their feedlot
and know which pens have poor air movement due to
physical structures or low lying areas and then avoid using
these pens for cattle that will be approaching slaughter
weights in mid to late summer.

Shade can be critical in determining whether cattle die
during extreme heat events, especially for dark-hided
cattle. For adequate cooling, plan for 20 to 40 square
feet of shade per animal and a height of at least 8 feet tall
to allow sufficient air movement under the shade. If the
shade structure has an east-west orientation, then the
ground under the shade will remain cooler during the
day. However, if mud is an issue then a north-south
orientation will increase drying as the shade moves
across the ground during the day. For drying to occur
the cattle will need to follow the shade onto hot ground.

Another factor that feedlots can address is fly control.
Biting flies annoy and stress cattle. If biting flies are
numerous, cattle will often bunch up, which can limit
their ability to cool. Minimizing breeding areas for flies
and applying insecticides early in summer to decrease fly
populations prior to heat stress times is worthwhile.
Pen management with sprinklers and bedding can mitigate
heat stress. Sprinklers can be used to increase evaporative
cooling and can reduce ground temperature. For best
results, sprinklers should thoroughly wet the animal and
not just put a mist in the air to cool the animal. If cattle
hides are not soaked, then the mist may actually settle
on the hair and trap the heat, making the cattle even
hotter. Before installing a misting system be sure the water
supply is adequate enough to provide drinking water and
sprinklers. Drinking water is more critical than a sprinkler
system, so make sure that adequate water resources are
before installing sprinklers. When installed, sprinklers
should be operated intermittently to avoid mud and
increased humidity. They should be placed away from
feed bunks and water tanks as shy or unaccustomed cattle
may reduce the feed or water intake to avoid them.
Cattle need to be introduced to sprinklers prior to
extreme heat. Those not used to sprinklers will try to
avoid the spray before becoming acclimated. Additionally,
sprinklers need to be used before cattle are in extreme
stress. Thermal shock from cold water can kill cattle that
are extremely stressed. Once sprinklers are utilized, they
need to be continued until the heat event is over and
cattle can manage on their own.

Figure 3. Steer blocking water tank to cool head. Photo courtesy of
G. Dewell.

Increasing the air flow can help cattle cope with
extreme heat events since evaporative cooling, whether
from perspiration or respiration, is improved with air
movement. Wind speed has been shown to be associated
with ability of cattle to regulate their heat load. Although
wind speed cannot be influenced, feedlots can increase
the cattle’s exposure to air movement. For example, if
pens have permanent wind breaks for winter weather
protection, consider constructing temporary wind breaks
for winter use so that air movement is not impeded during
the summer. Removing tall vegetation within 150 feet
of feedlot pens will also improve air movement. Tall,

Another consideration to reduce heat is to use light
colored bedding such as straw or corn stalks to provide
cooler areas within the pen and reduce radiant energy
absorption.

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Summary
To reduce the damage caused by heat stress, feedlots need
to monitor environmental temperatures throughout the
summer. When the heat index is above 90° F, cattle will
be under heat stress. In addition, hot weather following
precipitation can dramatically increase the potential for a
heat event. If overnight temperatures are above 70° F cattle
will have increased heat stress because of a retained heat
load. During times of increased heat stress, cattle should
be observed closely to identify if additional strategies
need to be implemented. For best results, feedlots need
to monitor for heat stress and implement strategies to
minimize impact on cattle to prevent severe death from
heat stress.

Authors

Prepared by G. Dewell, D.V.M., M.S., Ph.D., Beef Extension Veterinarian, Iowa State University, Veterinary Diagnostic and Production
Animal Medicine.
Cover photo by iStock/Thinkstock.
© Iowa State University Extension and Outreach 2018
This publication was peer-reviewed by two independent reviewers using a double-blind process.

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