Minimizing Heat Stress in Cattle
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Minimizing heat stress in cattle can make the difference between life and death in your herd. Hot weather, especially if it’s humid, can be hard on cattle, and they may be at risk for heatstroke. Cattle have fewer sweat glands than horses or humans, and can’t cool themselves efficiently by sweating. Instead, they resort to breathing faster (for more air exchange in the lungs) or panting with their mouth open if they are very hot.
Overheated animals will be panting and drooling — getting rid of some body heat with the saliva, and may sling saliva over themselves to get some cooling effect from evaporation. Hot cattle may stand in water if there’s a farm pond, ditch, or stream in their pasture, or stand next to a water trough.
On a sunny day, black cattle get hotter than red or light-colored cattle; the dark color absorbs more heat. Breeds with thick hair coats will also get hotter than a breed with a sleek, thin hair coat. The larger and fatter the cattle, the harder it is for them to disperse body heat, and the more adversely affected they are by hot weather. A fat cow or bull will overheat quicker than a small calf or a thin yearling, but baby calves may be at risk for dehydration if they get too hot and don’t feel like nursing, or are sick with scours. Diarrhea and hot weather can be a deadly combination.
Zebu breeds like Brahman and their crosses have more sweat glands and more heat tolerance (even if they are black) than British and European breeds. Dr. Stephen Blezinger, a cattle nutritionist in Sulphur Springs, Texas says the most common way that cattlemen practice minimizing heat stress in cattle in his part of the country (aside from making sure cattle have adequate shade and water) is to add Brahman genetics to their beef herds. Zebu cattle originated in warmer climates and are well adapted to heat.
“On a hot day, in a pasture where there are black Angus cattle and Brangus cattle, both breeds are black (a color that generally does not handle heat very well) but the Brangus will be grazing and the Angus are generally in the shade. Brangus are 3/8 Brahman and can handle heat better,” he says. Other composite breeds in the U.S. that mixed Brahman genetics with British and European breeds include the Beefmaster, Santa Gertrudis, Charbray, Simbrah, Braford, and Bramousin.
British and European breeds don’t do as well in a hot climate. Zebu cattle have different hair and more sweat glands and stay cooler. “One of the European breeds that tend to handle heat better than most is Braunvieh, but I’m not sure why,” Blezinger says.
Besides selecting cattle that can handle hot weather (if you live in a hot part of the country), another necessity for minimizing heat stress in cattle is adequate shade and water. “If you compromise on these, you lose performance (less weight gain in calves, less milk production in cows) simply because the cattle won’t eat as much when they are hot and miserable,” he says.
It’s also important to continually provide a salt lick, usually in a salt/mineral mix. Salt is crucial in hot weather because it is lost through sweating. The salt content of most mineral supplements is generally adequate. Cattle also need proper levels and sources of trace minerals in their mineral supplement. Blezinger says some studies show that when beef animals are stressed they excrete more zinc and copper, which must be replenished. Trace minerals are important to a strong immune system and good health in general.
“Another thing some cattlemen are feeding, though it needs more research, is enzyme products — a microbial culture such as Aspergillus oryzae (fungi), Bacillus subtilis (bacteria), or Saccharomyces cerevisiae (yeast). Enzyme activity facilitates better fiber digestion. We need cattle to be able to digest fiber very efficiently in summer and not produce as much heat during digestion,” he says. The normal heat production from fermentation and digestion is useful in cold weather for generating body heat but is detrimental in summer — creating more heat that the body must get rid of.
The most helpful thing you can do in hot weather is providing shade and plenty of fresh, clean, water that is cooler than 80 degrees F. If your water tank is out in the sun, or supplied by an over-ground hose or pipe that sits in the sun, water may get so hot that cattle won’t drink — and become dehydrated and at risk for heatstroke. You need shade not only for the animals but also for their water. If water is cool, they’ll drink and this will help cool them. Cattle need at least two gallons per 100 pounds of body weight, daily, and even more if the weather is hot and they are losing fluid through sweating and drooling.
If there’s only one water source and they crowd around it trying to drink or stand near or in it to cool themselves, they reduce any benefits of a breeze. The dominant animals may stand near the water and not allow timid ones to get a drink. You may need several water sources to keep cattle spaced out better.
Shade trees are helpful, especially if there’s some airflow through the trees. If there’s no natural shade you can create a roof on tall posts. A metal roof should be insulated. Otherwise, radiant heating will make it hotter underneath, like an oven. A roof should be at least 10 feet high, to allow air movement beneath it.
It’s also important to control biting flies. If cattle have to expend energy trying to get rid of flies (tail-swatting, kicking the belly, slinging their heads over their back) this creates more body heat. They also tend to bunch up when fighting flies — with less airflow around their bodies.
If you are moving cattle on a hot day and they start panting with mouths open and drooling, halt and let them rest. Don’t tag, vaccinate, dehorn, or wean on a hot day, and don’t haul or drive them very far during the heat of the day. Do it very early in the morning when it’s coolest.
Cattle are less at risk for heat stress in an arid climate, especially if it gets cooler at night. Low humidity enables them to lose heat through sweating and evaporation. If air temperature doesn’t drop below 70 degrees F at night, cattle start getting too hot. Heat is cumulative; if they can’t dissipate heat into the cooler night air, their body temperature slowly rises during a multi-day heat wave. If the heat lasts longer than three days, cattle may die.
If the air temperature drops below 70 degrees F at night, they have a window for heat loss and can often recover. If it stays hot at night, you need to find ways to cool cattle with sprinklers, shade, or fans. If cattle are outdoors, hope for clear nights with no clouds, to get some heat loss. The sky is a heat sink, on clear nights. But if it’s cloudy the heat sink is blocked and cattle can’t get rid of the heat.
Watch weather forecasts and temperature and humidity indexes. The combination of air temperature and humidity is what affects animals’ ability to dissipate body heat. Check the index to determine what the combination is — and whether it puts cattle into an alert stage, danger stage, or emergency stage. Even if the temperature is only in the upper 70s, if there is high humidity (70% or above), you may be in the alert stage. Once you get into the danger or emergency stage, you must do something quickly to save them, such as sprinkle them with cool water. At 75% humidity, the air temperature above 80 degrees F can cause heat stress in cattle. If humidity is less than 35%, they can handle 90 degrees F temperature without problems, and in a very dry climate, they can tolerate 100 degrees F.
How do you tell if a Cow is Stressed?
What precautions do you take when minimizing heat stress in cattle? We would love to hear from you in the comments below. The easiest-to-check indication of heat stress and elevated body temperature is respiration rate. Below 40 breaths per minute indicates a healthy, safe temperature. A respiration rate of 80 or higher is a sign of heat stress and cattle won’t eat. With a high respiration rate, it’s difficult to eat and they may not want to move. If it gets up to 120 it’s more serious. By the time it gets up to 160 breaths per minute their tongues are sticking out, they are drooling, and they have a real problem. You don’t have to count for a full minute to check respiration rate; count for 15 seconds and multiply by four, or for 30 seconds and double it.
Originally published in Countryside in September/October 2020 and regularly vetted for accuracy.