By Paul Beck, Oklahoma State University

Over the last few weeks we have had some really scorching temperatures with highs in the triple digits and lows in the upper 70’s. Coupled with the high humidity it is hard to get any relief for ourselves and our livestock. Below is the Beef Cattle Temperature Humidity Chart (Figure 1), it helps determine the risk level of heat stress given the temperature and the relative humidity. Notice the higher the humidity the lower the temperature that is cause for concern.

In hot summer conditions, heat transfer failures cause accumulation of body heat resulting in heat stress, reduced performance, animal discomfort, or death. When animals experience discomfort from heat stress, their behaviors change to reduce heat load (increased water consumption, decreased feed intake, seeking shade, standing in water, etc.).

The USDA Meat Animal Research Center published a scoring system to define heat stress in cattle based on panting score. This is a good indicator of heat stress because panting increases as the heat load increases. This scoring system is from 1 to 6, with 1 being slightly stressed to 6 being near death.

Water intake per unit of feed intake is twice as high during the summer than in the winter. Evaporation of moisture from the respiratory tract through panting is an important way for the animal to lose excess heat load. So, during heat stress water space availability becomes very important. During heat stress the linear water space increases from about 1 inch per head to 3 inches per head to allow for sufficient access to water. When temperatures are above 40° F, water intake should increase by 1 gallon for every 10° F increase in temperature.

Shade has been found to be beneficial to feedlot cattle, the greatest benefit of shade for finishing cattle is at the onset of the heat stress event. Cattle with shade have lower respiration rates and body temperatures when temperatures increase. Under heat stress, shaded finishing cattle in feedlots have increased average daily gain, hot carcass weights and dressing percentage as well as improved feed efficiency.

Cattle require 1.8 to 9.6 square yards per head depending on the size of the animal. Effective shade structure design depends on the thermal properties of the shade material, the ground cover under the shade, height of the structure, the amount of shade provided per animal, the level of ventilation (lower ventilation can trap heat under the structure), and the orientation of the structure.

Shade structures should be at least 12 feet high to reduce direct solar radiation and increase air movement in the shelter. Metal shades effectively block direct solar radiation, but it can accumulate heat and radiate it on the animal. Shade cloth allows more air movement and heat dissipation. Providing shade, if designed correctly, is an effective strategy to reduce heat load by reducing heat accumulation from direct solar radiation and has animal welfare benefits that can improve performance.

Finally, cattle handling should occur in the early morning before temperatures get too high. If there is little to no night cooling, cattle handling operations should be delayed until better conditions exist. Work cattle in small groups so that no groups are in holding areas longer than 20 to 30 minutes. Cattle should be handled easily to reduce stress and elevating core body temperature through increased activity.

Remember, if you are not comfortable neither are your livestock, so take steps to increase comfort of livestock during heat stress events.