Source: University of Minnesota Extension
- Temperatures above 80F and 90F put cattle at moderate and high risk, respectively.
- Heavy, dark-hided or poor immune system cattle are at higher risk.
- Heat stress causes poor feed intake, reduced daily gain and possibly death.
- Make sure your cattle have enough water, shelter from the sun and good airflow in their pens to prevent heat stress.
Causes of heat stress
High temperature and humidity are the main cause of heat stress. Cattle are at greater risk of heat stress as the combined air temperature and humidity rise (figure 1).
Wind speed and sunlight also affect heat stress in feedlot cattle.
In general, cattle are at moderate risk for heat stress when temperatures exceed 80 F and at high risk when temperatures exceed 90 F. Cattle are at greater risk during longer periods of warm weather and when night temperatures remain high (over 70 F).
Risk for heat stress
- Heavy cattle
- Dark-hided cattle
- Cattle with poor immune systems
Signs of heat stress
- General upset
- Grouping together
- Seeking shade
- Higher breathing rates
- Open-mouthed breathing
Impacts of heat stress
- Lower feed intake
- Reduced daily gain
- Death in extreme cases
Preventing heat stress
You can’t completely eliminate heat stress from your herd. But you can reduce the impacts of high heat and humidity on cattle health and performance. Follow short and long term weather forecasts to help you pick the most effective plan to prevent heat stress. Most plans require time to prepare and put in place.
Providing enough clean water is key during periods of heat stress. Cattle can drink over 20 gallons of water per day under heat stress. Make sure the water flows fast enough to meet the cattle’s increased drinking needs. The water should refill fast enough to provide the amount of water needed for a 24-hour period within four hours.
Reducing heat stress short-term
- Limit processing to the early morning if you must handle cattle when it’s hot and humid.
- Reduce the time cattle spend in holding pens.
- Use holding pens that offer shade
- Move cattle slowly to help reduce heat stress.
- Avoid handling cattle late in the evening and overnight.
- Cattle won’t be able to release heat from during the day, which leads to higher risk of heat stress the next day.
Offer 70 percent of daily feed after peak daytime temperatures if you feed cattle two or more times daily. This can help decrease the severity of heat stress events. Cattle will spend less time eating and moving during the heat of the day. Also heat from feed digestion will then occur during the cooler part of the day.
Reducing heat stress long-term
The University of Minnesota Rosemount Research Feedlot uses sprinklers to reduce cattle discomfort when it’s hot and humid. Sprinklers decrease animal body temperature and feedlot surface temperature.
Using sprinklers periodically will maximize their cooling effect. The goal is to thoroughly wet cattle in a short time and then allow them to dry before using the sprinkler again. Use sprinklers early in the morning or overnight to help cattle cool down before the heat of the day.
Sprinklers with large droplets wet the skin better than smaller droplets or mist. The skin must be wet for effective cooling. A wide spray sprinkler or multiple sprinklers per pen will prevent cattle from grouping.
Allow cattle to adjust to the sprinklers over several days before a heat event.
Sprinkler use isn’t ideal for every system. Sprinklers will increase humidity, which plays a role in heat stress. Thus only use sprinklers in areas with rapid air turnover. Humidity from sprinklers in pens with dead air may offset any benefits of cooling.
Shade lowers core body temperature and breathing rate of cattle. The impact of shade on animal performance varies, likely due to the following;
- The individual animal’s ability to handle heat stress
- Length and frequency of heat stress events
- Efficacy of shade provision
Provide 20 to 40 square feet of shade per head. Overcrowding can reduce the efficacy of shade for providing comfort.
The height of the shade structure affects airflow. Shade structures should be no less than seven feet tall. Make sure you place the structure in a spot where trees and other structures don’t block the wind.
Make sure structures can withstand stress from wind and snow.
Recouping your costs from shade structures through improved performance may be hard. But putting shade structures in sick pens or in pens with cattle prone to heat stress can be helpful.
Carefully consider airflow design in new confinement facilities.
You can improve existing facilities by:
- Opening ridgeline vents
- Installing positive pressure tubes
Check airflow through open feedlots as well. Each foot of vertical windbreak blocks airflow for 10 feet downwind. Consider winter and summer prevailing winds when planning windbreaks. Limited airflow can worsen heat stress. Ideally, don’t use pens with windbreaks during the summer. Often this isn’t feasible, but you should avoid stocking poor airflow pens with cattle at higher risk of heat stress.
Brown-Brandl, T. M., R. A. Eigenber, J. A. Nienaber, and G. L. Hahn. 2005. Dynamic response indicators of heat stress in shaded and non-shaded feedlot cattle, par 1: Analysis of indicators. Bio. Eng. 90(4):451-462.
Mader, T. L., J. M. Dahlquist, G. L. Hahn, and J. B. Gaughan. 1999. Shade and wind barrier effects on summertime feedlot cattle performance. J. Anim. Sci. 77(8):2065-2072.
Mader, T. L., M. S. Davis, and J. B. Gaughan. 2007. Effect of sprinkling on feedlot microclimate and cattle behavior. Int. J. of Biomet. 51(6):541-551.
by: Nicole Kenney Rambo, former Extension educator