Robert L. Eirich, Extension Educator
Dee Griffin, Extension Feedlot Veterinarian
Tami M. Brown-Brandl, Agricultural Engineer, U.S. Meat Animal Research Center
Roger A. Eigenberg, Agricultural Engineer, USMARC
Terry L. Mader, Emeriti Extension Beef Specialist
Jake J. Mayer, Project Engineer, Settje Agri-Services & Engineering
This NebGuide presents recommendations designed to help manage feedlot cattle during times of heat stress.
The thermocomfort zone varies greatly for beef cattle. Young cattle have a narrow comfort zone between 45 and 80°F. The comfort zone of feedlot cattle and mature cows will range from subzero temperatures in the winter to around 75°F in the summer, depending on body condition, hair coat length, and plane of nutrition. This wide comfort zone allows cattle to thrive under diverse climatic conditions with little or no need for shelter or protection. However, unlike humans, who can be reasonably comfortable on a warm spring day or when exposed to normal summer temperatures, feedlot cattle have difficulty coping with spring temperatures above 80°F and summer temperatures above 90°F. This is particularly true when humidity is high or wind speed is low.
Cattle’s heat adaptive mechanisms only allow for approximately 1°F adaptation per day; therefore, in the spring, 30 days are required for cattle to adapt to average temperature changes from 50°F to 80°F. Hair coat color can add to the heat stress cattle endure. Black-hided cattle suffer heat stress more severely than do either red or white cattle. It is currently estimated that over 50 percent of all cattle in the United States have black hair coats, and the percentage of black cattle is steadily increasing.
Managing heat stress in cattle starts by evaluating the potential for a heat stress emergency at your operation and developing a heat stress management plan. To the extent possible, anticipate the crisis so you can get maximum benefit from your plan. Evaluate the previous history of heat stress events or the potential for a heat stress event to occur at your location.
The United States Department of Agriculture-Agriculture Research Service (USDA-ARS) Roman L. Hruska U.S. Meat Animal Research Center (USMARC) maintains a website to help cattle managers understand cattle heat stress, plan for heat mitigation, and anticipate or forecast upcoming cattle heat stress events (http:// www.ars.usda.gov/npa/marc/heatstress or http://www.ars.usda.gov/Main/docs.htm?docid=21306).
Key elements to include in evaluating the potential of heat stress:
The following are procedures you should consider for your heat stress management plan. The first ones are more easily accomplished and may significantly improve the cattle’s ability to withstand heat stress and to help maintain their performance during times of heat stress. They should always be done when the possibility exists for the ambient temperature and relative humidity to reach the heat stress critical limits of cattle.
At temperatures above 80 degrees, cattle need more water than normal to prevent dehydration and allow heat to be dissipated through evaporative cooling (sweating) and urination. Consuming water is the quickest and most efficient method to reduce body temperature.
Measure the water delivery flow rate into every waterer in your feedyard. The rate needs to be measured when the system is under consumption pressure such as mid-morning or during the afternoon on a warm day. To measure the rate, slide a soft rubber tube over the water outlet to divert the water into a 5 gallon bucket and measure the gallons per minute into the bucket when the float is lowered. If the waterer is supplying a pen of 100 head of 1,000 lb cattle, the flow rate should provide approximately 500 gallons of water per hour during a heat stress event.
Additionally, cattle need to have access to the waterer so the linear space around the waterer is also important. There is not a good rule of thumb, but an accepted estimate is 2 to 4 inches per 1,000 lb; therefore, a pen of 100 head of 1,000 lb cattle would need at least 200 inches or 16.7 linear feet of watering space. That may sound like a lot, but, actually, the upper end of this estimate may be required in a critical heat stress event in which cattle could potentially die. It can be the factor that prevents cattle deaths.
Put out extra watering tanks, if needed. This should be done in advance of anticipated need so animals become accustomed to multiple water sources. Providing up to 3 inches of linear space per animal can be lifesaving in feedyards and ensures that all cattle can get water when needed. Having ample space for cattle to drink and stay cool can also be important in maintaining cattle gain and feed efficiency.
Add additional water tank space, so that each animal has access to at least 5 gallons per hour. Keeping waterers clean should encourage water consumption. Weekly scheduled waterer cleaning also improves the likelihood of finding any malfunctioning waterers.
Train everyone working around cattle to use low stress handling techniques. A series of classes taught by Tom Noffsinger is available online at the KSU Beef Cattle Institute website (http://beefcattleinstitute.org).
Processing cattle elevates body temperature 1 to 4°F, depending on environmental heat conditions and processing time. During heat stress periods, if cattle must be handled, work them in the early morning and absolutely not after 10 a.m. Your handling facility must have good airflow to the cattle and be shaded, if possible.
If there is any question about sufficient airflow, hang a 4- to 5-foot fan over the working facility and aim it at the cattle. While it may seem to make sense to work cattle after sundown, wait until the cattle have had at least six hours of night cooling before working them, i.e., wait until after midnight to start working cattle. Dissipation of body heat is needed at night and allows cattle to deal with heat stress more effectively during the day.
Work with the packers to schedule shipping cattle at night or at least early morning. Try to start loading early enough so that all cattle can arrive before 7 a.m. Most packers have sprinklers and can keep the cattle comfortable. If cattle arrive with body temperatures elevated above what would normally be expected, carcass defects such as dark cutters may be more common.
Cattle that must be handled during hot days should spend no more than 30 minutes in the handling facility (processing or hospital area). Avoiding cattle bunching is equally important. Most cattle working facilities have very poor wind movement, causing cattle to gain body heat while they are in these areas. A 30-minute time limit minimizes the heat gain and allows the body core temperature to return to normal more quickly so the feedlot animal can deal successfully with heat stress.
Arrange to have shade and sprinklers in those areas. Tubing (½ to ¾ inch) equipped with spray nozzles (one nozzle per five animals) placed overhead will improve the cooling in handling and holding areas. Select a larger droplet size for the nozzle when implemented in these areas.
Shifting the feeding schedule toward evening deliveries may help hold cattle on feed and even out the consumption patterns. Delivering 70 percent or more of the daily scheduled feed two to four hours after the peak ambient temperature of the day may decrease the roller coaster intake patterns often observed. Moving to a late-day feeding schedule may also minimize the subclinical acidosis that is thought to contribute to the problems seen in times of heat stress.
Epidemiologic research in 2000 by Laura Hungerford while at the University of Nebraska–Lincoln indicated that cattle on an “all natural” feeding program have a higher death loss during a severe heat stress event than cattle fed conventional rations containing an ionophore, a medication to help control liver abscesses, and in heifer rations containing a progesterone to control estrus. On the other hand, research by Guy Loneragan at West Texas A&M indicated beta agonist included in rations at the end of the feeding period increased the death loss in pens during the mid- to late summer months.
Lowering the energy level has been controversial, but some research indicates that lowering the energy content of the diet or using a storm ration may lower the heat load on the cattle. Visit with a qualified beef cattle nutritionist about how to manage changes in ration energy being fed to finishing cattle.
The following procedures may be more difficult to accomplish, because they require more intense planning, labor, and materials to implement. The key is to know your potential problem areas and focus your efforts on critical areas first.
Under heat stress conditions, the water delivery system needs to provide a minimum of 1.1 percent of body weight per hour; for a 1,000 lb feeder, this means 11 lb/hour, or about 1 ⅓ gal/hour. Ideally, a water system should be capable of delivering the amount of water required for an entire day’s needs within a four-hour period.
This can be calculated from line diameter and line pressure. For example, a ½-inch water line will provide 8 gallons of water a minute at 40 lb pressure and a ¾-inch water line will provide 23 gallons of water a minute. In other words, increasing the size of the water line by half will more than double the output.
Another important rule of thumb is that the water pressure drops by 25 percent for each elbow. Thus, a 90 degree turn on a water line that has 40 lb water pressure will drop the pressure to 30 lb, which means a 25 percent decrease in water flow rate. Additionally, there is a loss of water flow over the length of the pipe in which it travels (Figure 1).
Water reserve capacity is the amount of water stored and ready for cattle consumption. This can be at the water tank or in underground storage in large supply lines ready to deliver to the cattle’s watering tanks. An 8-foot round water tank that is 2 feet tall will hold approximately 700 gallons of water, enough for 7 gallons per head in a 100-head pen. Equally important, a tank of that size provides an additional 226 inches of linear watering space, giving more cattle an opportunity to have lifesaving access to water. Saving the life of one 1,400 lb feeder will pay for five water tanks of this size, which cost about $325 each.
Water reserve capacity and water flow rate calculations should always be performed before installing new watering systems. It is critical to know the existing water flow rate at each water tank. Water flow rates on automatic water tanks can be evaluated as noted previously. If deficiencies are identified in total supply or delivery at peak demand periods, additional supply and/or waterers must be added when temperatures are in the critical range. Alternatively, the cattle can be spread out to more pens so that the existing water supply can better serve critical needs.
Contact your local fire department or producer cooperative to access equipment that can deliver emergency water. Make sure livestock drinking water is safe and palatable. Large volume sprinklers can be installed if water supply is adequate. Sprinklers can effectively keep cattle below their upper critical temperature by increasing evaporative cooling and lowering ground temperature. Coverage of 10 to 15 square feet per head should be adequate. Remember, water requirements can easily double when wetting pens and sprinkling cattle. Plan accordingly.
Windbreaks may be beneficial in the winter, but are a serious detriment in times of heat stress. Identify feedlot areas having limited air movement. Consider abandoning pens that have airflow impeded by windbreaks, trees, buildings, and grain bins during critical heat stress, or at the least, avoid stocking these pens with cattle that have black hair coats or cattle that are projected to finish in summer through early fall.
Identify heavy, finished cattle, cattle new to the feedlot with a high risk for disease, and cattle with black hair coats, making sure to give these pens special attention to airflow. Tall vegetation, including growing crops, will obstruct airflow and provide a loafing area for the stable fly; remove tall vegetation 150 feet back from the perimeter of the pens. Consider building tall mounds in feedlot pens (see Figure 2). Mounds help prevent cattle from bunching and will usually enhance their exposure to air movement.
Shade reduces exposure to solar radiation, thereby reducing solar heat load on the animal, but does not affect air temperature. Major design considerations for shade structures are orientation, space, height, and roof construction:
Solely on the basis of performance, the economic benefit of shade may be difficult to calculate. However, research documents protection to feed intake decreases and maintenance of performance during heat events (Mader et al.). Research also documents the value of shade for decreasing the heat load on feeder cattle during heat stress events.
The USMARC has designed a unique stacked shade. Current research has not documented the value of this design to cattle performance. The design, when installed with a north-south orientation, will provide two shaded areas in the afternoon, one from each shade in the stack. The shades at the USMARC feedlot are installed on the fence line separating two pens.
To minimize interference with pen surface cleaning, the first shade is 15 feet high, well above the height of loaders used for pen cleaning. The second shade is 10 feet above the first shade. This louvered or stacked design casts a double shadow on the ground during the afternoon. The shade material is heavy duty plastic snow fence that has a ¼ inch cable along the edges and in the middle to add stability and strength to the plastic fencing. Thus far, the USMARC shades have withstood 60 MPH winds, 12-inch snow falls, and heavy ice.
For more information about the USMARC shade design contact Roger Eigenberg (Roger.Eigenberg@ARS.USDA.Gov); Tami Brown-Brandl (Tami.Brown-Brandl@ARS.USDA.Gov); or John Holman (John.Holman@ARS.USDA.Gov).
Stable flies cost cattle feeders a lot of money. Research by Jack Campbell at the UNL West Central Research and Extension Center found that just a few feeding females can decrease average daily gain (ADG) by as much as 5 percent. These flies torment cattle, making them bunch and disrupting animal cooling. When not feeding, stable flies loaf in tall grass, weeds, brush, trees, and under building eaves. Removing weeds and brush within 150 feet of pens and spraying the shaded areas of buildings with a residual insecticide will help control stable flies. Minimizing shallow pools of water or muddy areas around the feedlot will help eliminate breeding areas for flies.
Predicted hot weather following precipitation. It is the combined temperature, humidity, wind speed, and solar radiation (cloud cover) that determines the severity of heat stress. Days in the high 80s or 90s (°F) following a precipitation event can be extremely stressful, especially if the wind speed is below 5 miles per hour for extended periods of the day.
Monitor the upper critical temperature-humidity limits of cattle. Consider this limit reached when the Temperature-Humidity Index (THI) reaches 80 or the Heat Index (HI) reaches 100 (see Tables I and II).
Evening weather forecast for overnight temperatures to remain above 73°F. A potential heat stress crisis exists for cattle when there is little or no night cooling. Watch for days following nights in which the ambient temperatures do not drop below 70°F. Feedlot losses have been commonly reported when two or more consecutive days with THI values above 80 (or HI values above 100) have been tied together with nights in which the temperature stayed above 70°F.
Observing cattle will tell you when they are becoming uncomfortable from heat. The cattle will start to walk around the pen looking for an area of the pen that is more comfortable. They will start to salivate, and their respiratory rate will increase to 75 breaths per minute or above. They will begin to elevate their head to make it easier to breathe. As the condition progresses they will drop their heads and pull their ears back. They will position their body to minimize their exposure to the sun, generally facing the sun. See the cattle heat stress stage identification photos at the USMARC Heat Stress website (http://www.ars.usda.gov/Main/docs.htm?docid=15625).
During a heat wave, the first day when the wind is calm can be lethal to cattle. If your resources are limited, focus on managing heat stress for those cattle that may be most susceptible to heat stress. These include cattle with dark hides, cattle close to being finished, newly arrived high stress cattle, and cattle suffering from or recovering from illness.
Maintaining feedlot employee health during a heat crisis is critical. Employee safety always comes first. If they are suffering, they can’t do their best to care for the cattle, and managing heat stress can’t be accomplished. These recommendations are for personnel doing reasonably strenuous outdoor work when temperatures are in the critical range:
A critical heat stress emergency exists when the combined temperature and humidity levels fall in the dark gray areas of either the THI or HI table. Wind (airflow) can have a tremendous positive moderating impact on the adverse effects of high temperatures and humidities. Wind between 5 and 10 MPH can low the THI or HI by one unit per MPH wind speed. If there is little or no wind, expect cattle mortalities if there are more than three consecutive days in the GRAY area and night temperatures stay above 75°F.
Reference to commercial products or trade names is made with the understanding that no discrimination is intended of those not mentioned and no endorsement by University of Nebraska–Lincoln Extension is implied for those mentioned.
Barajas, R., P. Garces, and R. A. Zinn. 2013. Interactions of shade and feeding management on feedlot performance of crossbred. Professional Animal Scientist 29:645–651.
Mader, T. L., J. M. Dahlquist, G. L. Hahn, and J. B. Gaughan. 1999. Shade and wind barrier effects on summertime feedlot cattle performance. J. Anim. Sci. 77(8):2065–72.
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