By Sandi Alswager Karstens, Institute of Agriculture and Natural Resources
With summer just starting and temperatures already hitting 100 degrees, cattle producers need to take steps to ward off heat stress in their herds, a University of Nebraska-Lincoln beef specialist says.
Late spring 80-degree days with abundant rain are always welcome, but the recent rapid rise in temperature and sustained moderate to high levels of relative humidity can be disastrous for cattle that have not had a chance to get adapted to such conditions, says Terry Mader, beef specialist at UNL's Haskell Agricultural Laboratory near Concord.
"Cattle, as well as other animals and humans, usually need two to four weeks to adapt to the changes in environmental conditions we observed last week," Mader says. "Sunny days with temperatures above the mid-80s can be stressful, particularly if there is no wind and humidity is above 50 percent."
Cattle can begin to experience some level of heat stress when the heat index approaches 80 degrees, with most cattle being severely stressed when the heat index exceeds 100 degrees. Heat indices in excess of 110 already have been found in some parts of Nebraska.
Also, when early morning temperatures are above 70 and/or the heat indices are in the mid-70s or above, chances are cattle did not adequately cool down at night, and feedlot managers should be prepared to provide as much relief to cattle as possible during the day.
Water is probably the best avenue to dissipate heat, Mader says.
"The cattle don't have to be thirsty, but as cattle drink and pass water through their body, it removes a lot of heat in the process," he says.
Cattle normally take in about 5 to 6 gallons of water per day. However, when temperatures rise, that amount can double or even triple.
"It's important to have plenty of available water," he says. "When there is competition for water, it creates problems because the dominant animals will occupy waterer space and not allow other animals access."
If cattle are crowding around the watering trough, add more waterer capacity or move a portion of the animals to pens that will allow the animal to have adequate access to water, Mader says.
In an emergency, cattle can be sprayed with water to cool them down. However, once producers do that, they need to repeat or continue spraying until the heat subsides.
Spraying cattle with water will allow the animal to rapidly dissipate heat through evaporative cooling processes but this may limit the animal's ability to adapt to the heat. If the pen surface is dry, then wetting the pen will also provide relief to confined animals. It is always beneficial to start the wetting or cooling process in the morning before the cattle getting to hot.
Producers also should have an emergency plan in case water supplies are low or cut off, Mader adds.
In addition, producers should avoid handling cattle when it's hot and never after 10 a.m. Cattle body temperatures can rise an additional 0.5 to 3.5 degrees during handling.
Producers should feed cattle most of the day's feed several hours after the day's peak temperature in the late afternoon or evening. Avoid filling cattle up with feed late in the morning when added heat generated by digestion will peak around the hottest time of the day, he said.
Cattle yards also should be inspected so there aren't any structures that restrict airflow. Cutting down vegetation around pens and moving cattle away from windbreaks can all help. Building earth mounds in pens also can increase airflow by preventing cattle from bunching together. Other heat stress mitigation strategies include: provide shade, control biting flies and other parasites, keep very current on cattle marketings and be mindful of the effects of heat on personnel as well.
For more information about managing heat stress in feedlots, consult UNL Extension NebGuide G1409, Managing Feedlot Heat Stress.