CATTLE DO NOT HANDLE HEAT STRESS AS WELL AS HUMANS:
Richard Stowell PhD, UNL Associate Professor of Biological Systems Engineering
Dee Griffin DVM, UNL Beef Production Management Veterinarian
The thermo-comfort zone of feeder cattle and mature cows range from subzero temperatures in the winter to around 75 oF in the summer, depending on body condition, hair coat length, and plane of nutrition. Feeder cattle have difficulty coping with temperatures above 90 oF, especially when the local humidity is high and wind speed is low.
EVALUATE THE KEY HEAT STRESS ELEMENTS:
1. A long-term weather forecast of hotter-than-normal conditions signals early activation of a heat stress management plan.
2. High rainfall areas are susceptible to having high humidity, which makes it difficult for cattle to get rid of body heat. Humidity also keeps nighttime temperatures elevated, removing precious recovery time that cattle otherwise get during hot, dry conditions.
3. When there is little wind or airflow in pens is obstructed, the heat load on cattle intensifies. Wind is your friend when it comes to reducing heat stress.
4. Special measures are needed to help black-hided cattle and cattle that haven’t yet lost their winter hair coats.
DEVELOPING A HEAT STRESS MANAGEMENT PLAN:
Have ample water available.
The water required by cattle in hot weather doubles from 12 to 15 gallons per head to 24 to 30 gallons per head. At temperatures above 80 degrees, make sure you can provide up to 30 gallons of water per head. And, provide plenty of watering space. Bring additional watering tanks into pens if needed. In times of severe heat stress, feeder cattle many need as much as 12 inches of watering space around water tanks.
Avoid handling cattle.
Processing cattle can, by itself, elevate body temperature. If cattle must be handled during hot weather, work them in the early morning (prior to 8 a.m. and absolutely not after 10 a.m.) and in a shaded facility if possible. While it may seem to make sense to work cattle after sundown, wait until the cattle have had at least six hours of nighttime cooling before working them. On hot days, ensure that cattle spend no more than 30 minutes in the handling facility (processing or hospital area), i.e. only move 30 minutes worth of cattle at a time, and arrange to have shade and sprinklers in those areas.
Change feeding patterns and back off the energy.
Shifting the feeding schedule toward evening deliveries may help hold cattle on feed and even out consumption patterns. Research indicates that lowering the energy content of the diet may lower the heat load on the cattle.
Move cattle away from windbreaks. Windbreaks can be beneficial in the winter, but are a detriment in the summer. Windbreaks and other obstructions reduce airflow up to 10 feet downwind for every one foot in height, so a 40-foot-tall windbreak will obstruct airflow 400 feet downwind. Identify feedlot areas having limited air movement and, if possible, abandon these pens prior to heat waves. At least avoid feeding cattle that are projected to finish in summer or early fall in these pens.
Improve airflow in pens. Identify heavy, finished cattle and newly arrived high-risk cattle and give these pens special attention for airflow. Cut vegetation 150 feet back from the perimeter of the pens. Make mounds tall for summer, the taller the better. Tall mounds help prevent cattle bunching and will usually enhance cattle exposure to air movement. Cattle use them like bleachers in that every animal finds a spot that has some airflow.
Provide shade. Shade structures should provide approximately 20-40 sq. ft. of shaded area per feedlot animal, recognizing that few production benefits will be realized if animals are overcrowded. For emergency situations, 15-25 ft2/head can reduce mortality risks. For info, go to: http://www.ars.usda.gov/Main/docs.htm?docid=21306.
Be smart about sprinkling cattle/pens. In dry conditions and when airflow is provided or wind persists at rates that ensure rapid drying occurs, wetting cattle or pen surfaces can provide considerable cooling. Otherwise, adding water to the environment may compound the problem by increasing the humidity, insulating cattle hair coats, and creating mud.
LOOK FOR THE CLUES TO AN IMPENDING HEAT STRESS CRISIS:
First Clue: Predicted hot weather following precipitation. Days in the high 80’s or 90's (oF) following a rain event can be extremely stressful, especially if the wind speed is below 5 mph for extended periods.
Second Clue: The temperature-humidity index is above or is projected to exceed 80 THI (Temperature Humidity Index) or 90 HI (Heat Index), the upper critical limits of cattle.
Third Clue: Evening weather forecast is for overnight temperatures to remain above 73 oF or three nights in a row that stay above 70 oF. These conditions are more likely when the dew-point temperature approaches 70 oF.
Fourth Clue: Cattle tell you when they are becoming hot if you observe them regularly. They start to move around the pen looking for an area that is more comfortable. Their respiratory rates increase (above 75 breaths per minute is a reliable symptom of heat stress) and they start to pant and slobber. Cattle elevate their heads to make it easier to breathe and they position their bodies to minimize exposure to the sun, generally facing the sun, and increase exposure to airflow.
REMEMBER HUMAN SAFETY:
Minimize strenuous work during hot conditions. If personnel must do hard work, take breaks each hour by spending 10-20 minutes doing less strenuous activity, preferably in the shade.
Force water consumption. Drink one to two quarts of water per hour.
Use a buddy system to make sure adequate water is consumed, workload alternates between strenuous work and periods of light work, and early signs of heat exhaustion are detected. Signs of heat exhaustion include mood changes, emotional responses, and confusion.
If a person gets overheated, he or she should not return to strenuous work that day. Instead, working inside or taking the rest of the day off is advisable. Failure to do this may result in the person developing heat stroke.