By: Donald Stotts, Oklahoma State University
Most areas of Oklahoma experience 70 or more days each year with temperatures that exceed 90 degrees Fahrenheit, providing ample reason for cattle producers to guard against heat stress in their herds.
Earl Ward, Oklahoma State University Cooperative Extension Northeast District livestock specialist, reminds producers that cattle’s upper critical temperature is not based off of the ambient temperature alone but also the humidity and evaporation rate.
“Humidity is an additional stress that intensifies ambient temperature problems by making body heat dissipation more difficult,” he said. “In other words, it can be tough to cool off in Oklahoma during the summer, for people and cattle.”
High humidity contributes to the likelihood of heat stroke or prostration because water evaporation from the oral and nasal cavities is decreased, in spite of rapid panting, a heat regulatory device in cattle.
“Although cattle sweat, the primary mechanism they have to remove internal heat is by panting to increase evapotranspiration, which is accomplished much more efficiently in low humidity environments,” Ward said.
Signs of heat stress include slobbering, heavy panting, open mouth breathing and lack of coordination. Severe cases may include depression and trembling that require some type of low stress intervention.
“If water is applied to cattle for cooling, it is important that a large droplet size be applied,” Ward said. “Misting water does not reach the hide and only adds humidity to the breathing environment.”
Fortunately, overheating in cattle can be prevented under most management conditions. Allowing cattle access to cool water and mineral supplements is a must during hot summertime weather.
“If possible, producers should increase the number of watering locations in a pasture utilizing temporary troughs or tubs,” said Marty New, Oklahoma State University Cooperative Extension Southwest District livestock specialist. “Cattle tend to bunch up around watering areas, which will reduce air flow and increase heat stress.”
Extra watering troughs or tubs will scatter the cattle over a larger area and into smaller groups. Also, be aware that water consumption will increase by more than 50 percent when temperatures are at or above 90 degrees Fahrenheit.
“Check water sources frequently and have a back-up plan in place to ensure water availability for each pasture,” New said. “Producers should also be aware that lower water levels in farm ponds can have higher concentrations of pollutants – thus greatly diminishing water quality – so alternative water sources may be needed.”
Access to shade and air circulation should be provided, if possible. If natural shade is not available, producers should construct suitable structures.
“Ideally, the shade material would be mounted on a frame with the material at least 10 feet in the air and open on all sides,” New said. “Air flow is critical to provide maximum cattle cooling and comfort.”
If the unit is portable, producers can move the structure to reduce the “mud-hole effect” that can develop around permanent structures. For cattle in a confinement lot, light-colored bedding is cooler to lie on than bare, dark soil.
Also, feeding confinement cattle later in the day allows the heat produced by rumen function to be dispersed at night when it is cooler, reminds Ward.
“It’s typically a good idea to work cattle before 8 a.m. during hot weather, and all cattle work should be completed by 10 a.m.,” he said. “While it may seem to make sense to work cattle after sundown, they may need at least six hours of night cooling before enough heat is dissipated to enable them to cool down from an extremely hot day.”
Cattle that must be handled during hot weather should spend less than 30 minutes in the working facility, according to OSU recommendations. Drylot pens and corrals loaded with cattle will have little if any air circulation.
“Cattle will gain heat constantly when in these areas,” Ward said. “By limiting the cattle’s time in a working facility, the producer can help limit the animal’s heat gain and therefore the heat stress.”
Again, the most basic rule is to make every effort to provide cattle access to cool, fresh water, especially for animals that are in close, confined areas for any length of time.
“During hot weather, cattle will drink more than 1 percent of their body weight per hour,” New said. “Producers need to be certain that water supply lines are capable of keeping up with demand when working cattle during hot weather.”
Excitable cattle will be even more prone to heat stress if handled at high environmental temperatures.
“If animals are going to have limited access to water under stressful conditions such as shipping by truck or trailer, they should be allowed water prior to further stressful situations,” New said.
New and Ward point out that it is fortunate most cattle handling for health and production purposes in Oklahoma typically occurs in the relatively cooler weather of spring and fall, resulting in a reduced need for cattle handling in the heat of summer.
Oklahoma is the nation’s fifth-leading producer of cattle and calves, according to USDA National Agricultural Statistics Service data.