Reduce heat stress in cattle to avoid production losses

SIOUX FALLS, S.D. — Cattle with heat stress can result in lower average daily gains, reduced milk production and decreased conception rates.

“The perfect temperature for cattle is 55 degrees so anytime it is above that we’ve got to start thinking about what we can do to make sure we’re not compromising animal welfare,” said Spencer Wolter, veterinarian at Southwest Veterinary Services, Farmers Business Network’s partner.

“The average cow in the U.S. has 96 days of heat stress,” said Wolter during a webinar hosted by FBN.

“Cattle have apocrine sweat glands which are not great at their job,” the veterinarian said. “Panting is a big way cattle cool down, but panting is not efficient.”

A cow’s rumen creates a lot of heat.

“When we feed cattle, we’re really feeding the bugs in the rumen,” Wolter said. “The breaking down of the feed causes the rumen to spike in temperature which results in higher cattle temperatures.”

To dissipate the heat that cattle have stored during the day, the temperature needs to be below 70 degrees for at least six hours during the night, the veterinarian said.

“If you’ve had three days where the night temperature has not been below 70 degrees, you might want to hold off on working those cattle,” he advised.

Feedlot cattle over 1,000 pounds and dark or black cattle are at higher risk for heat stress.

“Also chronic lunger’s — cattle that have scarred lung tissue because if they have compromised lungs, their panting is even more ineffective,” the veterinarian said. “Make sure you are culling those cattle because they won’t be able to handle the heat.”

Wolter discussed the stages of heat stress that start with a slightly elevated breathing rate, restless attitude and perching.

“In stage two the breathing rate will continue to increase, they will drool and they start grouping together because they are a herding animal,” he said.

During stage three, cattle will be foaming and at stage four there will be open mouth breathing.

“At stage five you will see their tongue protruding and for stage six the cattle will have labored breathing, their head is down and they will isolate from the herd which is really out of character for a bovine animal,” Wolter said. “Cattle in stages five or six can die from heat stress.”

Heat stress can result in a 5% to 10% reduction in cow’s milk production, said Erika Nagorske, a veterinarian at Southwest Veterinary Services.

“If cows are producing less milk, their offspring is getting less milk which could lead to a reduction in weaning weights and average daily gains,” Nagorske said.

“You’re also going to see decreased conception rates because cows won’t settle a pregnancy because their bodies are so stressed with heat,” she said. “Bulls will have lower sperm motility and concentration.”

Heat stress can also impact immune function.

“It will be more difficult for cattle to fight off disease pressure,” Nagorske said. “It might also be harder for cattle to respond to vaccinations so you might not get the best response to a vaccine.”

Research in dairy cattle indicates heat stress effects fetal programming.

“They have been tracking cows and if their heat stress is managed during the dry period, they give birth to heavier, healthier calves, they produce more milk in the following lactation and they have a better transition period because they have a better immune system during that process,” Nagorske said.

“Cows that have heat stress in late gestation have calves with reduced milk production and they can be genetically programmed differently,” she said.

Nagorske encourages cattlemen to process cattle early in the morning or late in the evening to avoid heat stress.

“You are putting them in a packed area which usually doesn’t have the best ventilation so they have an increased body temperature, it’s stressful and typically water is unavailable,” she said. “It’s a lot more than they are warm, the cattle might not have the best response to a vaccine.”

During hot days, Wolter said, access to water is critical. The typical recommendation is to provide two inches of space on the water tank per animal.

“But during hot times, you should increase that to three inches per head,” he advised.

In addition, the amount of water should also increase on hot days.

“In the winter, cattle drink one gallon of water per 100 pounds of bodyweight, but in the summer it’s two-plus gallons per 100 pounds of bodyweight,” Wolter said.

Cattlemen can change the time when they feed cattle to help reduce cattle’s body temperature.

“The rumen is in peak production four to six hours after feeding,” Wolter said.

“Don’t feed cattle at 8 or 9 a.m. because the peak body temperature will be during the hottest part of the day,” he said. “Shift to feeding early or feed at 3 to 4 p.m. so the rumen temperature will peak at 7 to 8 p.m., when it’s cooling off.”

Shade is critical for cattle that are in dry lots.

“It can be up to 20 degrees cooler in the shade,” Wolter said. “Provide from 20 to 40 square feet of shade per animal.”

Five to eight feet hills are ideal in dry lots.

“That gives you the best benefit from the extra wind so the cattle are above other cattle standing and the fence line,” the veterinarian said. “Remove tall vegetation within 150 feet of the feedlot pens so it doesn’t block the breeze.”

Airflow and sprinklers, Wolter said, need to happen together.

“Just soaking cattle is helpful, but the evaporative cooling from the airflow is the most beneficial for cattle,” he said. “Use cool water with the sprinklers and run short times, but frequently.”