Extreme heat can kill cattle, and the most susceptible cattle are the largest and most valuable. One tool we can use to measure the level of stress on cattle is the National Weather Service’s Heat Index.
A combination of the temperature and humidity is used to calculate the heat index. It should be noted that according to NOAA the heat index is calculated assuming some shade and light breeze; in full exposure to the sun you should increase the heat index by up to 15 degrees. Heat indices over 80 is an area of caution, over 90 is extreme caution, over 103 is Danger and over 125 is Extreme Danger. For example, when temperatures are in the mid-90’s and humidity is above 50% the heat index is above 103 and we begin to run the risk of losing cattle.
- daytime heat indices over 100
- a lack of night cooling-when heat indices stay above 80 all night long
- newly arrived or newly processed cattle
- black hided cattle
- heavy cattle
- cattle with a high degree of finish
As you can see, the most valuable cattle (heavy, finished, black-hided) are at the greatest risk of death loss.
Here are some actions you can use to reduce heat stress and save cattle:
A. Immediate, Emergency Actions
- Apply water to the cattle any way you can to reduce body temperature
- Apply water to the pen surface to reduce the heat exposure to the cattle (pen surfaces can easily go over 1500 F)
- Allow automatic waterers to overflow and run across the pen surface
- Make more water available to the cattle to drink in open tanks
- Get the cattle under shade if possible, but be sure there is also plenty of air movement
- Cold water enemas may help save down cattle
B. Strategic Actions (when you have time to plan ahead)
- Set up sprinkler systems that can water the cattle and the pen surface
- Automate them with a timer and/or a temperature/humidity controller
- Evaporation provides great cooling affect, so set the sprinklers to run intermittently instead of continuously
- Sprinkling the pen surface will have a longer lasting effect than sprinkling the cattle
- Don’t sprinkle around the waterers, this avoids cattle congregating here and allows cattle easier access to the waterers
- Be prepared with extra waterers
- Be sure your well pump has plenty of capacity
- Provide at least 20 ft2 of shade per head with a height at least 10 ft above the pen surface
- During extreme heat stress, shade reduced death loss from 4.8% to .2%*
- Be sure there is plenty of air movement, if the shade is an open front building with no back doors or ridge vents it could turn into an oven if packed full of cattle.
- Avoid pens with windbreaks that will restrict breezes during the summer
- East and Southeast facing pens reduced death loss during extreme heat stress, from 6.3% to 2.7%.*
- Feed most or all of the ration in the early evening, avoid feeding in the morning
- The cattle will produce metabolic heat from eating when the ambient temperature is lower.
- The feed will heat less in the bunk and stay in better condition, resulting in better dry matter intakes.
- MGA fed to heifers during extreme heat stress reduced death loss from 6.2% to 3.8%*
- Don’t load or process cattle during heat stress, or at least wait until after dark
- Plan to have your finished cattle shipped before the hottest days of the summer
- During extreme heat stress death loss was 5-6% for cattle >1000#, and 3.4% for cattle <1000#*
* Loy & Busby, Iowa State University Extension, survey of 36 feedyards that experienced extreme heat stress