Risk of Heat Stress Rises this Week

The USDA's cattle heat-stress forecast shows much of the eastern and central states under risk of dangerous to emergency heat stress as this week progresses.
The USDA's cattle heat-stress forecast shows much of the eastern and central states under risk of dangerous to emergency heat stress as this week progresses.

The July weather pattern is posing to offer challenges this week for feedlot operators and cattle producers. Above average rain fall across the state has created greater humidity and has deteriorated pen conditions.  The seven-day forecast is calling for above average temperatures creating heat indexes that will reach critical heat stress emergency.  Thursday and Friday July 18 and 19 will be critical days across the state as little cloud cover is expected and wind speeds will be at or below 10 mph across the region.

With the uncertainty of wind, take precautions.  Utilize empty pen space to allow cattle greater room and access to water. Supplemental water tanks may be needed to insure ample water intake to those animals exhibiting signs of stress. Consider placing cattle in pens where cattle can be away from windbreaks to catch what little wind we may have. The following link outlines steps to take during heat episodes - https://BQA.unl.edu/heat-stress-resources.  Dr. Terry Mader, UNL Professor Emerti provided great insight on heat stress and steps to take in the following webinar https://beef.unl.edu/webinar/heat-stress-mitigation-feedlot-cattle .

Additional steps maybe considered. Work by Dr. Robbi Prichard has shown manipulating the amount of feed delivered the day before the highest heat index will help cattle keep their internal temperatures lower. Prichard said “By cutting the morning feeding by 25% we were able to keep cattle cooler in the hottest part of the day.  The cattle recovered sooner and ate their feeding in the afternoon and had less heat load throughout the night.”

Why is this? The contributions of the heat of fermentation, digestion, and metabolism of the feed consumed in the morning become critical on the day that cattle hit the heat stress limit. If we take that feed away before cattle back away from feed we greatly improve the survival of the cattle. To do this, we watch the heat index forecasts closely. For example, cattle may seem fine today but if there is not enough night cooling (hours below 70 F with wind) and the heat index will remain high the next day, one should consider taking away some of the morning feed delivery. This lowers the heat load midafternoon, which reduces the amount of heat that must be shed overnight.  Prichard said "We typically reduce the morning feed delivery by 25% today, and that may increase to a 50% reduction the morning of high heat index, depending on conditions and cattle status. If we wait for cattle to refuse feed it is too late."  Afternoon deliveries are not adjusted. If the cattle can and do eat afternoon deliveries, that feed generates heat during the night when there are lower temperatures and less solar gain, lowering the total heat load accumulating in the body. "It may seem like we are reducing DMI too much, but if we don't make these adjustments the feed refusals that will be coming in the days ahead will actually represent more pounds of feed than we are taking away with the feed call."

When asked about increasing the roughage in the diets Pritchard commented, "A move to higher roughage diets is not recommended. Under normal conditions cattle will react to a diet change by increasing meal size and forage has proportionally higher heat of fermentation than concentrates. Both of these factors will exacerbate the heat load problem. Staying with the current diet and controlling intake works best for us."

The Nebraska State Climate Office’s Nebraska Mesonet site calculates a cattle comfort index score.  Stonie Cooper, Manager of the Nebraska Mesonet reported that cattle comfort indexes will reach close to a 120 in parts of the state.  “Precautions should be taken to provide additional care to not only cattle on feed but to all animals across the state”.

Additional information on heat stress can be found at https://Beef.UNL.edu

For more information on heat stress in cattle, see these articles from BovineVetOnline:

Reduce Heat Stress in Cattle

Heat stress and youngstock

Heat Stress Affects Unborn Calves

Warnings Signs of Heat Stress in Cattle


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