Summer is officially here, and temperatures are beginning to heat up across the nation. With increasing temperatures, special attention is needed when it comes to mitigating heat, especially those animals being housed in a dry lot. While some only consider temperature when assessing the effects of heat, other environmental factors such as humidity, air movement, and solar radiation contribute to the heat load cattle experience.

During times of heat stress, producers may observe limited or reduced feed intake, increased respiration (observed as panting), and crowding around water tanks. Furthermore, during extreme heat stress events, cattle may succumb to these conditions if unable to decrease their body temperature. 

Because cattle do not effectively dissipate heat through sweating, they are unable to regulate their core body temperature like humans or other animals. Cattle must maintain normal body temperature to sustain essential physiological processes. The range of temperature within which cattle do not use additional energy to maintain core body temperature is referred to as the thermoneutral zone. This zone generally ranges from 32°F (lower critical temperature) to 75°F (upper critical temperature; UCT) for cattle but can vary depending on metabolic size and adaptation to the environment. When temperatures exceed the UCT, cattle expend energy in an attempt to dissipate heat. Panting and elevated respiration and heart rate are signs that this is occurring.

During periods of extreme heat, the physiological systems that cattle rely on to reduce core body temperature are often unable to keep up during the day. As a result, this heat load must dissipate, often times at night, when temperatures drop below 70°F for 4 to 6 hours. If night temperatures do not drop below 70°F for at least 4 hours, cattle have no chance to decrease their core temperature and recover before the next episode of heat exposure. Producers should monitor weather frequently for potential heat events and keep an eye out for predicted temperatures in the high 80s and 90s, especially following a rain, and in situations where the wind speed is going to be less than 5 mph for several days.

Cattle producers must work to prevent or address environmental conditions that approach cattle’s heat thresholds to maintain optimal performance and health. Additionally, environmental conditions, even if not extreme, should be considered when deciding how and when to handle cattle.

One of the most critical times producers will need to implement strategies to prevent heat stress is when scheduling handling or transporting cattle. During these times, cattle will be experiencing a “double dose” of stress. Stress from handling and transport, and stress from the heat.  

Beef Quality Assurance (BQA) guidelines suggest that producers should strive to refrain from handling or transporting cattle between 11 a.m. and 4 p.m., the hottest hours of the day. However, guideline authors understand that the beef industry does not stop because of a hot day. Therefore, BQA guidelines suggest that producers schedule handling or transport of cattle before the temperature-humidity index (THI) exceeds 74. If cattle must be handled when the THI is ≥ 75, the BQA program encourages beef producers to use precautions and implement strategies to best protect cattle during extreme heat events.

The best way for producers to determine when heat conditions have reached the point in which they need to implement strategies to reduce cattle heat stress is by using the Cattle Temperature Humidity Index (THI; Figure 1). As an example, when the temperature is 98°F and the humidity is 30%, then the THI is 83, which is just inside the danger zone for cattle.

Producers can take steps to mitigate heat stress prior to an extreme heat event by:

• Marketing finished or nearly finished cattle prior to the event.
• If unable to market, move finished cattle to pens deemed to be less prone to heat stress (pens with shade, greater wind exposure, greater water access, or where bedding may be delivered easily).
• Place sick or compromised cattle in bedded or shaded hospital pens.
• Avoid receiving cattle during extreme heat events.
• Assign heat remediation tasks to one lead individual in team. Empower this individual to delegate heat mitigation tasks to other individuals, as appropriate.
• Make plans to do any cattle processing before the heat event.
• Plan to conduct pen riding and sick cattle pulling in the early morning hours (prior to 11 a.m.).
• Remove any movable barriers that prevent air flow.
• If possible, set up shades, but only if 12 ft high and at least 16 square feet of space per head can be shaded.
• Add and supply water stock tanks on fence lines away from existing water tanks.
• If possible, set up sprinklers and turn them on ahead of heat event.
• Plan to have additional water (accessed through a local fire department or crop producers) and water wagons on hand.
• Under emergency conditions a watering trough slip-in can be built where water tankers can deliver water in the feed bunk. Cap the ends of 20-foot culvert pipe sections (12- to 18-inch in diameter to fit at the bottom of a feeding bunk) before cutting lengthwise to produce two identical size troughs.  Burn the edges with a flame torch to smooth sharp edges resulting from the cut.  This results in a trough that can be slipped to the bottom of the feed bunk.  A single 20-foot section should add at least five watering spaces and 130 gallons to the watering tanks in the pen.  Keeping these slips full of water should ease the pressure on watering tanks during hot and still days.  

During immediate times of heat stress, producers should:  

• Provide additional water and space around water tanks for each animal. When the temperature is above 80°F, cattle require nearly twice as much water (up to 30 gallons per head per day).
• Consider reducing the amount of feed delivered in the morning to help lower the heat load on cattle, starting the morning before a heat event occurs.
• Consider adding an extra 10 percentage units of roughage to finishing diets or feed storm diets (remove diets containing fat).
• Improve air flow by incorporating tall mounds and placing cattle in pens with fewer windbreaks in the summer.
• Removal of excess manure is critical. When manure builds up, it holds moisture and increases humidity.
• Use sprinklers with a large droplet size; however, limit use when humidity is high.
• Bedding pens can reduce pen surface temperature up to 25°F by reflecting solar radiation about 10 to 20 square feet per head.
• Providing shade to reduce the heat load on cattle up to 20°F. However, it is important to have adequate space per animal to prevent overcrowding.
• Limit the amount of time cattle spend in handling facilities where heat stress may be more significant, and work cattle more prone to heat stress first, earlier in the day, or later if conditions are moderate; for example, process larger cattle during periods of lower THI.
• When transporting cattle, a good practice is to reduce the load by 10% to improve air flow.
• Limit the amount of time the animals are on the trailer and reduce the amount of time the trailer is not moving providing ventilation and air flow.

Producers should be aware that the following should be considered high-priority pens and deserve additional attention:

• Finished or near finished cattle.
• Black cattle that haven't shed winter coats.
• High intake cattle.
• Cattle (pen mates) with previous history of digestive or respiratory illness.
• Pens with poor wind movement (north slopes, wind breaks, in valleys).
• Pens with no shade.
• Pens with restricted water access or poor water flow.
• Pens with no sprinklers.

Being proactive rather than reactive is important for avoiding any train wrecks when it comes to heat stress. For more information, see the Heat Stress Mitigation in Feedlot Cattle webinar https://beef.unl.edu/webinar/heat-stress-mitigation-feedlot-cattle or the Feedlot Heat Stress Information and Management Guide https://extensionpublications.unl.edu/assets/pdf/g2266.pdf. You can also checkout the Nebraska BQA Extreme Heat resources at https://bqa.unl.edu/resource-library.

Interviews with the authors of BeefWatch newsletter articles become available throughout the month of publication and are accessible at https://go.unl.edu/podcast.  You can subscribe to the BeefWatch newsletter here: http://go.unl.edu/Beefwatch_subscribe