Dee Griffin DVM, Beef Production Management Veterinarian,
Cattle do not handle heat stress as well as humans
Unlike humans, who can be reasonably comfortable when exposed to normal summer temperatures, feedlot cattle have difficulty coping with temperatures above 90° F. This is particularly true when humidity is high or wind-speed is low, especially when cattle have had little or no chance to adapt to excessive heat loads.
Clues to an impending heat stress crisis:
- Temperature-Humidity Index (THI) above 84 (Heat Index (HI) above 100)
- Combined heat and lack of cooling (little or no wind and little night cooling)
- Wind below 5 MPH (the THI decreases about 1 unit per 1 MPH wind)
- Little night cooling (THI stays above 70)
- Dark or black-hided cattle
Activate emergency plans when temperatures combined with humidity are forecast to be in the critical range for livestock. During a heat wave, the first calm wind day can be lethal to cattle. If resources are limited, focus on managing heat stress for the most susceptible cattle, including those with dark hides, cattle on all-natural feeding programs, cattle close to being finished, newly arrived high-stress cattle, and cattle suffering from illness or recovering from illness.
Evaluate the potential of a heat stress emergency
To the extent possible, anticipate the crisis so you can get maximum benefit from your plan. Key elements to be included in your evaluation are:
1. The normal annual rainfall in your area. High rainfall areas are more susceptible to having high humidity.
2. Precipitation above normal, particularly if wet weather continues into the summer months.
3. Long-term weather forecast of hotter than normal conditions, which should signal early activation of a heat stress management plant.
4. Obstruction to airflow in cattle pens. Wind breaks and other airflow obstructions will create calm airflow up to 10 feet downwind for every one foot in height. A windbreak 10 feet high will obstruct airflow 100 feet downwind. (Wind is your friend: 1 MPH wind will decrease the Temperature Humidity Index (THI) about 1 unit).
5. Availability of water for watering cattle, and wetting down cattle or pen. Animals on average can easily consume one to two gallons of water per hour, under normal environmental conditions. Watering space and water flow to watering troughs should also be evaluated to ensure cattle are protected from dehydration.
6. Special protection, water supply and airflow may be need to help black-hided cattle and cattle on all-natural feeding (no implants or feed medications) programs keep cool.
Develop a heat stress plan
Elements in a heat stress plan should include:
- Have ample water available. At temperatures above 80°F degrees, cattle may need in excess of two gallons of water per hour per 100 lbs. of body weight. Consuming water is the quickest and most efficient method to reduce body temperature. Putting out extra watering tanks should be done in advance of anticipated need so animals become used to multiple water sources. Providing 5 ½ inches of linear space per animal can be lifesaving in feedyards and ensure that all cattle can get water. Add additional water tank space so that cattle have access to at least five gallons per hour. Keep waterers clean to encourage water consumption.
- Avoid handling cattle if possible. Processing cattle can elevate body temperature ½ to 3 ½ degrees, depending on cattle temperature and processing time. During heat stress periods, if cattle must be handled, 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. Wait until the cattle have had at least six hours of night cooling before working. Dissipation of body heat is needed at night and allows cattle to deal more effectively with daytime heat stress. Ship cattle at night or early morning. Load early enough so that all cattle can arrive before 7 a.m.
- Cattle handled on hot days should spend no more than 30 minutes in the processing or hospital facility. Avoid cattle bunching as most facilities have very poor wind movement causing cattle to gain body heat. A 30-minute time limit minimizes the heat gain and allows the body core temperature to return to normal quicker. Arrange to have shade and sprinklers in those areas. Tubing (1/2 to ¾ inch) equipped with spray nozzles (one nozzle per five animals) placed overhead will improve the cooling in handling and holding areas.
- Change feeding patterns and consider backing off energy. Shifting the feeding schedule to evening deliveries may help hold cattle on feed and even out consumption patterns. Deliver 70% or more of the daily scheduled feed two to four hours after the peak ambient temperature of the day has been reached to decrease variable intake patterns. A late day feeding schedule may also minimize subclinical acidosis thought to contribute to the problems seen in times of heat stress. Research indicates that lowering the energy content of the diet or using a storm ration may lower the heat load on the cattle.
- Assess water supply and delivery capacity to allow all cattle to get half their daily need within an hour. Shoulder to shoulder feeder cattle can require up to 32 inches of liner space. If cattle can get their required water in 10 minutes it would mean each mature feeder would require 5½ inches of liner watering space. Under heat stress conditions, the system needs to deliver a minimum of 1.1% of body weight per hour; for a 1000 lb animal, this means 11 lb/hr, or about 1⅓ gal/hr. Ideally, a water system should be capable of delivering within a 4-hour period, the amount of water required for an entire day’s needs.
- Make arrangements for emergency water. Contact the local fire department or 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.
- Move cattle away from wind breaks. Identify feedlot areas having limited air movement. Identify heavy, finished cattle and newly arrived high-risk cattle in the feedlot and give these pens special attention in regard to airflow. Cut tall vegetation 150 feet back from the perimeter of the pens. Consider moving these cattle to shaded pens or pens with better wind flow. Consider building earth mounds in feedlot pens to help prevent cattle from bunching and enhance exposure to air movement.
- Provide shade to reduce exposure to solar radiation and heat load. The most effective orientation is east-west to keep ground under shade cool. The shade structure should provide approximately 20-40 sq. ft. of floor space per feedlot animal. For emergency situations to reduce mortality risks, 15-25 sq. ft,/head can be beneficial. Shade height should be in the range of 7 to 14 ft.; the higher the shade, the greater the air movement.
Control biting flies. Stable flies cause cattle to bunch and disrupt animal cooling.