Producers can beat the heat on the range

A hot cow tries to cool off on a hot summer day. | Cheryl Waldner photo

There is not much that can be done to cool the weather, but cattle can be managed in the summer to prevent heat stress

During a hot summer, cattle need adequate water and shade.

The shade can be from trees or brush, or manmade.

“Don’t clear off every acre for crops; leave a few trees for winter windbreaks and summer shade,” says Bart Lardner of the University of Saskatchewan.

“Feedlots often put up overhead shade structures. In a pasture, you might want to make sure there are some trees for cattle to get into,” Lardner says.

In a pasture with no shade, portable awnings can be provided.

On very hot days, it’s best to not handle the cattle or move them very far because exertion may lead to heat stress.

“If it will be hot, postpone that activity until a cooler day, or do it very early in the morning,” he says.

Signs of heat stress are obvious.

“The cattle will be standing with legs apart, panting with mouth open and tongues out,” says Lardner.

He says they may congregate around a water source or wade out into a pond, dugout or stream to try to cool off. If you are moving cattle and some of them start breathing with their mouths open, you need to stop and let them rest for a while.

Certain toxins can affect blood circulation and make it harder for cattle to handle heat or cold.

“We have done research on ergot and if there are high concentrations of ergot in the grain or in the feed, cattle cannot handle the heat. This is very similar to fescue toxicosis. The cattle start to show signs of heat stress —panting and (be) lethargic.”

In hot, dry weather a person should check cattle and water sources often. Cattle could be in serious trouble if they are short of water and suffering from heat stress at the same time. A dehydrated animal will suffer heat stress much quicker than an animal with adequate water.

Heat stress can sometimes be unexpected and people are not prepared for this in regions that are generally not considered at risk for this problem.

Don Spiers, professor emeritus at the University of Missouri, has been involved with research on heat stress for years. He says that large animals and fat animals have more trouble dissipating heat than smaller, leaner animals. Dark-coloured animals and those with more body fat have the most problem with heat.

High heat combined with high humidity can be a deadly combination.

“Here at the university, we developed a free app called Thermal Aid that anyone can download on their iPhone and program it for beef or dairy and put in their location. It accesses a weather station near your area, and gives you the ambient temperature, humidity and predictions of what those will be. Combined, the temperature and humidity provide the temperature humidity index. This gives an indication of how stressful it will be for your animals,” he says.

“It gives predictions for three to four days and changes colour depending on how hot it is or will be. It goes from green (no stress) to yellow (warning) to red (danger). If you know that tomorrow will be in the red zone, you don’t want to be moving, processing or shipping cattle,” he says.

Cattle out on pasture need adequate shade and water. “Years ago, extension people were telling people to get rid of the trees — to maximize productive acres — which was a big mistake,” says Spiers. Trees provide windbreaks and shelter in winter and shade in summer.

“Some producers use portable shade structures that they move from pasture to pasture. Cattle need a way to get out of direct sunlight. The metabolic rate of a cow, especially a fast-growing animal, is much higher than ours. We may feel comfortable at a certain temperature but these animals will be hot,” he says.

The rumen creates heat during fermentation digestion, so cattle must be able to dissipate body heat or it continues to build up. “Humans have a lighter build and sweat more than cattle do. Cattle also have more hair, which tends to insulate and hold in the heat,” says Spiers.

If ambient temperature drops at night, this gives cattle a chance to dissipate excess body heat, but if it stays hot, especially if it’s humid, they have no chance to cool off. Heat continues to build in their bodies, resulting in heat stress or deaths from heat stroke after a few days.

Cattle standing with legs apart and panting with their mouths open and tongues out is an obvious sign of heat stress. | Don Spiers photo

He says nighttime temperatures needs to get below 26 C to allow cattle to cool off. In heat waves where night temperature doesn’t drop below 21 C for three days, cattle start to suffer.

“Nighttime cooling makes a huge difference. If night temperatures stay above (21 C) you might need to find ways to cool cattle. If you try to cool them, night is the best time to do it; you have a better chance to get their temperature lower.”

This is hard to do when cattle are out on pasture, but some producers have been creative. They could rig up sprinklers in pastures where cattle could go under a misting of water to help cool them.

If cattle get too hot, conception rates drop, and cows may suffer from early pregnancy loss. The problem is trying to see the correlation between heat stress and reproduction because it is so delayed, Spiers says.

Some producers are calving later rather than during the cold weather of February or March to be more in synch with nature, but this means breeding must occur during the heat of summer.

Producers using artificial insemination will have to handle those cows during hot weather, which is an additional stress, and conception rates may drop, he says.

“What the parents are exposed to, such as what the cow is experiencing during pregnancy, can affect the embryo or fetus, or even affect the eggs in the female. The female is born with all the eggs for her lifetime. If she suffers heat stress that reduces blood flow to those eggs (because she is routing more of the blood to the skin to try to dissipate body heat). The eggs that are developing could also be malnourished and not the prime eggs you’d want for creating offspring,” he says.

Studies in dairy cattle have looked at heat stress affecting the fetus in utero, and how it affects the calf.

“We are not sure what to tell producers when they ask about the best time to breed cattle.” There are plusses and minuses to every breeding season. Producer must figure out what works best for their own situation.

Some people with valuable bulls have put them in an air-conditioned barn during the hottest weather so they are not as adversely affected by heat stress and can breed more cows, he says.

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