"Compared to many other animals, cattle are much less able to withstand heat stress. That inability can not only have a detrimental effect on performance but can cause significant death loss during periods of extreme heat accompanied by increased levels of humidity," Krantz said, pointing to the Livestock Weather Hazard Guide graph.
Krantz added that due to the abnormally cool temperatures experienced throughout the month of July, the total reversal of temperature patterns could potentially impose even more stress on cattle that are not acclimated to these conditions.
This is evident by reviewing the Heat Stress Chart, developed during a July 2011 weather event by Dennis Todey, South Dakota State Climatologist & SDSU Extension Climate Specialist. Although cattle had been experiencing heat stress above the "heat load limit" (horizontal line) as early as July 16, 2011, most of the cattle death loss in eastern South Dakota did not occur until July19 and 20. "The accumulated heat load from the elapsed timeframe spent above the heat load limit resulted in cattle being unable to get rid of that heat load. Consequently, hundreds of death losses were reported," Krantz said.
To minimize the risk to cattle during a heat wave, Krantz encourages feedlot operators to develop a plan of action before hot and humid conditions hit. "Proactive and reactive plans developed prior to these conditions can help mitigate cattle losses," he said.
The action plan needs to consider ways to lessen heat stress brought on by air temperature and relative humidity.
"The combination of high temperatures plus high relative humidity is particularly dangerous, especially when there is little to no night-time cooling," Rusche said. "Solar radiation and air movement aren't accounted for in this index, but these factors are major components in determining how high temperatures affect cattle."
Water access is vitally important to maintain the well-being of cattle during hot weather. Water consumption at 90 degrees Fahrenheit can be 2.5 times higher compared to intakes at 70 degrees Fahrenheit.
Prior to a heat wave, Rusche encourages feedlot operators to ensure the water system has enough capacity so there is enough water consistently available to satisfy cattle demand.
"There should be at least 3-linear inches of trough access per head. Extra tanks may need to be provided to ensure enough access and holding capacity. Making sure the tanks stay clean will help make sure that water intake isn't being limited," Rusche said.
Heat stress can also be reduced by using sprinklers to cool cattle and the ground. "It's important to make sure the droplet size is large enough so that there isn't a mist created," Rusche said. "A mist might only add to the heat stress by increasing humidity."
Sprinkling should be introduced to cattle prior to extreme heat and begin before the cattle are under significant heat stress. "Waiting until the cattle are overheated is too late," Rusche said. "An additional supply of emergency water may need to be acquired so that the supply system can meet both sprinkler and drinking water demand."
Providing shade is another way to mitigate heat stress. "Shade will reduce the amount of radiant heat load the cattle would face and reduce the surface temperature of the ground," Rusche said. SDSU Extension has produced a video that shows how shades and temporary water tanks can be utilized on the farm:
Providing a layer of light colored bedding also can reduce the temperature of the soil surface in a pen that does not have shade. Applying bedding to mounds or lot surfaces can reduce those surface temperatures which sometimes are as much as 30 degrees to 50 degrees hotter than bedded surfaces. Wetting the bedding can create an even greater effect.
Removing barriers to air movement such as temporary windbreaks or tall vegetation that's close to the pens will help increase airflow and provide some relief.
When possible, Rusche said to avoid working cattle during heat waves to minimize losses.
If it is absolutely necessary to move or work cattle during hot weather, Krantz said work should be done early in the morning (completed before 9 a.m.) or very late and should be limited to no more than 30 minutes. "The core temperature of cattle peaks about two hours after the peak air temperature and it takes roughly six hours for cattle to dissipate their heat load. So even if it cools down at night the carryover effects from earlier in the day could be enough to cause problems if cattle were worked," he said.
Some additional pro-active measures:
- If the weather was extreme today, is expected to be extreme tomorrow, and there will be little relief tonight, wetting cattle and the feedlot surface tonight will be helpful.
- Pay particular attention to cattle that are at higher risk for heat stress. These include heavy cattle, those with dark hides, and those with past health problems.
- Fly control measures, such as fogging cattle or grooming lots for manure management purposes, can reduce crowding and consequently the stress load on cattle from fighting them.
- Feed 70 percent or more of the daily ration in the late afternoon or evening. Delaying feeding times has been shown to reduce the animal's peak body temperature.
- One method to determine whether or not to reduce morning feed deliveries is to monitor early morning respiration rates. If cattle are still breathing faster at 6 or 7 a.m. that's an indication that the heat load didn't dissipate overnight and offering less feed and sprinkling more often would be warranted.
- Feeding MGA to heifers has been associated with less death loss due to heat stress, presumable because of less riding activity.
- As well intended as a pro-active plan might be, cattle feeders need to additionally develop a reactionary plan as well:
- Continue the process of wetting cattle down. Once you have started it is essential to continue that practice throughout the duration of the heat event.
- Monitor weather forecasts continually for unexpected changes such as declining wind speeds, changing sky conditions and predicted overnight low temperatures.
- The use of fire trucks or water trucks/trailers with pumps are effective for cooling cattle; However, caution should be taken with this practice to avoid cattle running away in response to the water or noise and making matters worse.
Other resources that are available to help producers manage through a heat wave include the USDA Heat Stress Forecast Maps which can be found at www.ars.usda.gov; the SDSU Climate and Weather page: climate.sdstate.edu/climate_site/climate.htm and iGrow.org where additional materials related to heat stress in cattle can be found.