More pounds, more heat tolerant

Jul 1, 2011
by DTN

Take 90 F, add in about 98 percent humidity, and when you start to feel like you’re wading through the day, you begin to see what cattlemen like Darrel Haynes deal with all summer long.

Haynes runs a cow/calf and feeder operation in Cullman, AL. He’s a fourthgeneration cattleman with a sizable corn/soybean rotation and several hundred acres of permanent pasture. Like most southern cattle producers, Haynes has struggled with managing heat stress in his herd over the years. He’s found two things that really make a difference: one, a little Brahman blood; and two, Max Q novel endophyte fescue.

Brahman bloodlines.

Haynes started reintroducing Brahman blood into his mostly Angus and Hereford herd about seven years ago. He had a hard time finding some F1 type heifers and ended up in south Louisiana where he bought Brahman cows from a producer. Later he found some full-blood Brahman bulls and a few heifers. He bred the heifers to an Angus bull.

“Today we have 150 F1type cows, and we’re working to build that number up,” explains Haynes. “We haven’t seen any problems with getting those F1s bred back, which was a concern. And we’re definitely seeing more heat tolerance on those animals. They are out grazing in the middle of the day when my other cows are lying in the shade.”

Going novel. Another big focus of Haynes’ heat stress management program is awareness of the fungus in fescue. He tries to dilute the effect of the fungus with mixed permanent pastures that include Bermudas, native grasses and clovers.

But in areas where the fescue has gotten too hot, he’s taken on the task of refurbishing pastures, clearing out Kentucky 31 and putting in Max Q.

“We started to refurbish pastures about eight years ago,” he says. “It’s a long process. We do one or two pastures every year. It’s difficult because it means forfeiting the use of that pasture for the year. We offset that by cropping it, and going in with the Max Q in the fall. That gives us income off the acreage.”

To date, he has transitioned about 25 percent of his pastures, and wants to take that to 75 percent of total pasture acreage. As he’s moved through the process, Haynes says he learned one thing about Max Q no one told him: You may have to reduce stocking rates.

“In our operation, we found the animals simply grazed more on the novel endophytes. As a result, we’ve reduced stocking rates on those pastures. It’s not a problem because those animals weigh more. So in terms of pounds, it’s working for us.”

Minerals and management. Veterinarian Ken McMillan of Cropwell, AL, says taking a preventive approach to heat stress is key in any operation. He urges producers to make every attempt to begin to systematically eliminate toxic fescues. But where that’s not feasible, he says to look for ways to dilute the negative effects like Haynes has done.

Overseeding with clovers or other grasses is a good start. Also, clip seed heads in the spring to decrease the amount of toxin cattle ingest. A good, free choice mineral balanced for the environment, time of year and life stage of the cattle is especially important when heat and humidity are high.

“It can take six hours or more after the sun goes down for a cow’s body temperature to return to normal. That’s why I always recommend working cattle early in the morning during the summer.”

“Increased water consumption leads to increased mineral loss,” explains Mc-Millan. “Evaporative losses from increased respiration, increased urination, and even the limited sweating ability increase mineral loss.

“There is some evidence that higher levels of certain minerals can help cattle deal better with fescue toxicity. A seaweed extract called Tasco-Forage has shown some promise in research trials for decreasing body temperatures of cattle on toxic fescue.”

Signs of stress. If cattle start to suffer from heat stress, McMillan says in the early stages, feed consumption will decrease and cattle will spend more time in muddy areas, ponds or streams if accessible. Increased respiratory rates and breathing problems might be evident. Look for long, dull coats and decreased milk production.

Abortions or early embryonic death also are problems. Cow and bull fertility will decrease.

Open-mouthed breathing is common when heat stress becomes severe. Eventually, cattle will lie down and may be unresponsive and unable to rise. At this point, even medical intervention may not be able to save the animals.

“Cattle with open-mouthed breathing, who are wobbly when they walk or are recumbent, may benefit from immediate medical attention, but many may die in spite of it,” says the veterinarian. “Cool-water enemas, cool IV or oral fluids, sprinkling the animal with water and using fans to increase evaporation may help. But heat stroke leads to imbalances in the body and edema in the brain. Many of these animals will die.”

Avoid reaching that point with lots of clean, cool water and some common sense. McMillan says it’s especially important to remember when working cattle in the summer months that it takes a long time for temperatures to drop.

“It can take six hours or more after the sun goes down for a cow’s body temperature to return to normal. That’s why I always recommend working cattle early in the morning during the summer. And if possible, provide some means of air circulation and shade.”

Forecasting heat stress

Researcher Tami Brown- Brandl with the USDA’s Agricultural Research Service in Nebraska has developed a list of 11 factors that make cattle more or less prone to heat stress. These include color, species, gender, temperament, previous exposure to heat stress, hair thickness, age, Body Condition Score, current health, previous health problems and previous cases of pneumonia. Of these factors, two keys are coat color and whether or not an animal has had pneumonia.

A breathing rate equation and a predictive map have been developed to help identify times when cattle are most likely to experience heat stress.

Breathing rate equation.

This is a mathematical equation to help a producer determine when animals are getting close to the danger level. The formula is used when temperatures are above 80 F:

Breathing rate = (2.83 x temperature) (0.58 x humidity) - (0.76 x wind speed) (0.039 x solar radiation) - 196.4.

Temperatures are in Fahrenheit, and humidity is not a percent, but the whole number. Wind speed is in miles per hour. If no on-site data is available for solar radiation, use 1,000 watts per meter.

A score of less than 90 puts animals in the normal category; 90 to 110 puts them into the alert category; 110 to 130 means danger; and above 130 is an emergency situation.

Predictive Map. This map, available at www. (click Cattle Heat Stress), uses data from the National Weather Service, combined with heat stress research, to determine areas where steps should be taken to reduce the impact of heat. — DTN