Page 11 - MWC 8-10-2023s

The Midwest Cattleman · August 10, 2023 · P11
Managing Heat Stress Important for Cow-Calf Operations

By Mark Z. Johnson fall of THI is that it does not ture exceeds

Heat stress is caused by a account for solar radiation 80 degrees
combination of environmen- and wind speed which can af- Fahrenheit.
tal factors including tempera- fect heat load of cattle. During Ideally water
ture, relative humidity, solar times of increased heat stress sources should
radiation, air movement and cattle should be observed not be exposed
precipitation. During the closely to identify if addition- directly to the
summer we need to assess al strategies need to be imple- sun.
the heat stress that cattle mented. Initially feed intake •Shade is
are under. Cattle on pasture will drop off and cattle be- critical, es-
are not as susceptible to heat come restless. As heat stress pecially for
stress as feedlot cattle be- increases cattle will begin to black cattle.
cause they have the ability slobber and respiration rates To be effective
to seek shade, water and air will increase. Eventually, cat- there needs
movement to cool themselves. tle will begin to group togeth- to be 20 to 40
In addition, radiant heat er. In severe heat stress cattle square feet of
from dirt or concrete surface will begin open mouth breath- shade per an-
is increased for feedlot cat- ing with a labored effort. imal. If using a mechanical movement under the shade.
tle. At temperatures above Actions to Minimize Heat shade structure, an east-west •Increasing the air flow
80 degrees Fahrenheit cattle Stress orientation will permit the can help cattle cope with
can endure physiologic stress •In the summer months, ground under the shade to re- extreme heat events. Wind
trying to deal with their heat cattle should be worked main cooler. However, if mud speed has been shown to be
load. Although cattle at this only early in the morning. is an issue, then a north-south associated with ability of cat-
temperature are not at risk Working and handling cattle orientation will increase dry- tle to regulate their heat load.
of dying, they will have an in- will elevate their body tem- ing as the shade moves across Although we cannot influence
creased maintenance require- perature and cattle should the ground during the day. wind speed, we can ensure
ment to cope with the heat. not wait in processing areas The height of the shade struc- that there are no restrictions
Compared to other ani- longer than 30 minutes when ture should be greater than 8 to air movement such as hay
mals, cattle can’t dissipate it is hot. Do not work cattle feet tall to allow sufficient air continued on page 25
their heat load very effec- in the evening, even if it has
tively. Cattle do not sweat cooled off, it is not recommend-
effectively and rely on respi- ed. Cattle’s core temperature
ration to cool themselves. A peaks 2 hours after peak en-
compounding factor on top of vironmental temperature. It
climatic conditions is the fer- also takes at least 6 hours
mentation process within the for cattle to dissipate their
rumen generates additional heat load. Therefore, if peak
heat that cattle need to dis- temperature occurred at 4:00
sipate. Heat production from pm cattle will not have recov-
feed intake peaks 4 to 6 hours ered from that heat load until
after feeding. Since cattle do after 12:00 am and it will be
not dissipate heat effectively, later than that before cattle
they accumulate a heat load have fully recovered from the
during the day and dissipate entire day’s heat load.
heat at night when it is cool- •Provide ample amounts
er. Any time the Tempera- of cool water. The water re-
ture-Humidity Index (THI) is quirements of cattle increase
above 80 cattle will be under during heat stress. Cattle lose
heat stress. Hot weather fol- water from increased respira-
lowing precipitation can in- tion and perspiration. Addi-
crease the THI dramatically. tionally, consumption of water
Just as importantly, when is the quickest method for cat-
overnight temperatures are tle to reduce their core body
above 70 degrees Fahrenheit temperature. Rule of thumb
cattle will have increased is that cattle need 3 inches of
heat stress. During extreme linear water space per head
weather conditions with in- during the summer. Extra
sufficient environmental water tanks should be intro-
cooling at night cattle will duced prior to extreme heat
accumulate heat that they events so that cattle become
cannot disperse. Therefore, a accustomed to them. Multiple
temperature-humidity index cattle need to be able to drink
(THI) alone may not predict at the same time. Waterers
cattle heat stress because it need to be kept clean and cool.
does not account for accumu- Water intake actually de-
lated heat load. Another short creases when water tempera-