Heat Stress and Beef Cattle

In the hottest part of summer, cattle managers need to consider heat stress in their stock and how it can be mitigated. It is better to plan and strategize ahead of time rather than react after the heat wave begins.

Whether in a pasture or in a feedlot, cattle can suffer heat stress. Environmental conditions that contribute to heat stress include minimal cloud cover, little to no air movement, high relative humidity, and high overnight low temperatures (above 70°F).

Researchers at the Meat Animal Research Center (MARC) have identified four primary areas that influence an animal's response to heat stress. Those four factors are genetics, health, production status, and previous exposure to heat.

Lighter colored cattle generally show less heat stress than darker colored breeds. Research has shown that in a group of genetically closely related cattle with different hide colors, cattle with dark hides had a 2°F higher core body temperature. And, calmer cattle have been shown to be more heat-tolerant than excitable ones.

MARC research has shown that feedlot cattle treated for pneumonia at any time between birth and slaughter have a 10.5% higher respiration rate under stressful conditions than their untreated peers—another good reason for implementing preconditioning programs for calves.

Heavy feedlot cattle are at more risk. Additionally, very young and very old animals are at more risk.

What cattle are eating plays a role in heat stress. Excessive protein levels can be problematic. This could occur in pastures and in feedlots. The excess nitrogen in the protein must be biochemically removed and excreted through urine, using energy and generating heat in the process. Additionally, there are differences between cattle fed grain and those fed only hay. Feeds such as corn contribute less to the heat of fermentation than hay. High-quality forages produce less heat of fermentation than low-quality forages.

With all this said, what can we do? Some of these things we can control, and some we can't.

Shade is important. Most of our feedlots in this part of the country have a fair amount of space under roof. Provide shade to pasture cattle during hot weather. Pasture managers need to recognize that allowing cattle to lounge in shade all summer (when it may not be necessary) will, over time, result in 'nutrient creep' from the pastures to shade areas and also result in less efficient utilization of pasture.

Water intake is critical. Ambient temperatures in the mid-90s can increase cattle water requirements by 2.5 times compared to 70°F. Water trough capacity and refill rate become very important in this situation. Most experts agree that cattle need three linear inches of water tank space per head during hot weather. If necessary, introduce additional water tanks ahead of a heatwave so cattle can become accustomed to them. Ensure that refill rates are sufficient to prevent cattle intake from exceeding refill capacity. One guideline I found is that a 1,000-pound animal requires approximately 1.5 gallons of water per hour during hot weather.

The timing of feeding can make a difference. There isn't much we can do about that with pastured cattle, but a feedlot manager may be able to adjust feeding times to allow more of the heat of digestion to occur during the lower nighttime temperatures.

If cattle are housed in a barn, ensure that adequate ventilation is provided. This may involve opening up all doors and windows, adding fans, or providing access to an outside pen with shade.

Take action to control flies. This involves not only applying repellents and control products, but also eliminating areas that support fly breeding. Biting flies can cause cattle to bunch up, which reduces evaporative cooling via air movement. Fly problems can affect both pasture and feedlot cattle.

If at all possible, try to avoid working cattle during extreme heat. Schedule any handling to be done first thing in the morning, as daylight allows. Working cattle in the evening is not recommended, as cattle are still dissipating heat from the day.

A livestock weather hazard guide is available at the Noble Foundation website.

Information for this article was sourced from OSU, ISU, SDSU, MU, UWEX, NDSU, MARC, and the Samuel Roberts Noble Foundation.