That Bright Sunny Day May Stress Your Beef Cattle Herd
Good shade will help prevent heat stress and so will properly grazed pastures. Taller grass or bedding is good insulation from the radiant sun that keeps the ground cool.
By Ellen H. Brisendine
That beautiful, sunny, summer day can be a stressful time for beef cattle on pastures.
Guy Ellis, D.V.M., with Merck Animal Health, says a day with a heat index of 80 will cause most beef cattle to feel stress from heat.
Variables such as air temperature, humidity, wind speed or lack of a breeze, and the hide color of your beef cattle can contribute to heat stress.
Ellis says, “On a 90 degree day, with the sun shining, low humidity and a little breeze, if the cattle have some shade to get under they are probably not suffering from heat stress. But on an 85 degree day, at 70 percent humidity, with no wind, they could be suffering heat stress.”
The visual signs of heat stress in beef cattle on pasture are increased respiration or panting, open-mouth breathing, and reduced feed consumption.
Cattle suffering from heat stress will sometimes drool to dissipate heat. And ranchers may see their cattle “laid up in the shade more during the day or in the evening when they really need to be out grazing. When they’re spending more energy trying to cool off, they really aren’t too interested in eating as much,” he says.
Hidden effects of heat stress
Some effects of heat stress may not be so apparent. Decreased fertility is one effect. Ellis says heat stress may interfere with an embryo’s ability to implant in the cow’s uterus, “therefore, even though she conceived, she may not be able to carry the embryo because of the implantation issue.”
Heat stress can affect the bulls in your herd, too. “If it’s hot outside and it doesn’t cool off at night, it can affect the fertility of bulls and the semen quality. You may not notice anything until you notice a diminished calf crop,” he says.
Cattle temperatures rise during the day
The temperature in your beef cattle normally rises during the day and slowly dissipates overnight, Ellis says. “If it doesn’t cool off at night, if it doesn’t get below 80 to 85 degrees, then the cattle don’t dissipate heat like they should. Their internal temperatures start building again in the morning and that’s when you can run into some really dangerous situations.”
Good shade will help prevent heat stress, and so will properly grazed pastures.
“You don’t want an animal lying on the hot, bare ground. Taller grass or bedding is good insulation that keeps the ground cool from the radiant sun.”
Soil thermometers will show a difference of up to 20 degrees in the surface temperature of bare ground compared to grass-covered ground.
Provide many sources of abundant, clean, cool water
Shade and soil cover are important for keeping cattle cool. Abundant fresh water is imperative, Ellis says. “A cow will drink 2 to 3 times more water when she’s having to deal with heat stress. It helps if that water is cool,” he says. Ideally, the cool water could come from a shaded water tank or from water lines that run “in some deep grass or along the fence where the grass may have grown up. It helps the cattle to dissipate heat if the water lines supplying them are not in direct sunlight, so the cattle aren’t having to drink warm or hot water.”
Provide multiple sources of water so the cattle don’t overheat when traveling to distant watering points.
Lactating cows may be under greater stress during higher heat-index days. They are trying to keep their own bodies cool with water intake and their calf is also trying to increase fluid intake.
Fly control helps manage heat stress
Summer is peak fly season, and in August and September, cattle expend a great deal of energy fighting flies. “Good fly control will help the cattle deal with heat stress because they won’t have to expend as much energy fighting them off,” Ellis says.
Get an early start when working cattle
Working in the cooler morning hours makes sense for humans and for the cattle. Ellis says this is particularly true if nighttime temperatures stayed above 80 degrees F.
“We don’t want to agitate the cattle or move them around too much during the hotter times of the day, as that would cause them additional stress. Common sense will tell you to not stress your herd during the heat of the day. They can be pushed too far.”
Calves born earlier this year may be due for vaccinations in the summer months. Ellis points out that working in the cooler morning hours is best for the calves being vaccinated and for the vaccines themselves.
“As a veterinarian, I’ve come across ranchers who are a little behind in working cattle. They try to keep up with their work and end up having to work some cattle after lunch because they couldn’t get to them early in the morning. That can be disastrous. Not only will your vaccines or medications not work properly, but it’s very stressful for the animal and can lead to some acute heat-related deaths.”
As for the vaccines, “The minute you get them out of the cooler or mix them appropriately, they’re starting to lose their effectiveness, so the longer they stay warm or at room temperature or above, the less effective they are.”
Ellis says a styrofoam cooler with holes in the side and ice packs inside is an inexpensive way to keep vaccines cool. There are also specially-designed coolers, including one designed by Merck Animal Health, to keep medicines and syringes cool while cattle are being worked through the chute.
Keep your cattle cool, keep yourself cool, and provide abundant water, Ellis says. “I really want to emphasize that cattle need abundant water and abundant water sources. Cattle consume a lot of water in the hotter months.”
Sunny Day Stress is excerpted from the May 2018 issue of The Cattleman magazine.