Heat stress in feedlot cattle can cause huge losses to the feeding industry.

The detrimental effects of heat stress can range from a loss of gain and feed efficiency to cattle death. Core body temperature of fed cattle becomes critical based on a variety of factors, including body condition (worse in heavy cattle), nutrition, health, breed and acclimation to a new environment.

Cattle begin feeling the effects of heat at about 70 degrees. Stress levels can become critical with temperatures starting at as low as 85 degrees with a high humidity and limited night cooling. Cattle can feel the effect of heat, even when humans are comfortable. A good rule of thumb is that if you’re using air conditioning in your vehicle, your cattle are likely feeling some heat stress.

Signs of heat stress in feedlot cattle

• Crowding around water tanks or under shade
• Panting and increased salivating
• Increased respiration rates
  • Moderate stress: 80 to 120 breaths per minute
  • High stress: 120 to 160 breaths per minute
  • Severe stress: over 160 breaths per minute
• Gasping and lethargic

Cattle feed intake is often the first indication of heat stress. As cattle warm up, an initial drop in feed intake may not be noticed. As cattle continue heating up, feed intake drops more significantly and cattle begin using additional energy to help keep cool. The result of this process is often reduced production and efficiency, and once performance level drops – it can be very difficult to regain. Some of this loss is carried all the way through to the packinghouse.

Tips to minimize heat stress in cattle

1. Water availability. Water consumption is the most efficient and fastest way for cattle to reduce body temperature. In higher temperature situations, consumption of water should increase as well. At temperatures above 80 degrees, cattle may need more than two gallons per hour for each 100 pounds of bodyweight. In a 10,000-head feedlot with an average animal size of 800 pounds, the daily requirement would total almost four million gallons. Water quality is also important. In areas with high sulfur water, intake may be reduced. An alternate supply of high-quality water may be essential during this time. 
2. Cattle feeding time. One strategy for reducing the heat load on cattle is to offer a majority of the feed late in the afternoon. Cattle consuming diets during the late evening hours may be better able to cope with the heat load that results from fermentation. The heat load would occur during the coolest part of the day. 
3. Cattle ration adjustments. What you feed cattle during periods of hot weather can impact body temperature. In a paper presented at the 2007 Southwest Nutrition and Management Conference by Dr. Terry Mader, three diets were compared. The summary showed that cattle fed a high roughage diet had the lowest body temperatures, cattle fed a restricted intake 6% roughage diet had intermediate body temperatures and cattle fed an ad-lib 6% roughage diet had the highest body temperatures. 
4. Spraying. During hot weather, spraying cattle with water can help reduce body temperature. It also helps reduce the ground temperature. However, this process requires cattle be thoroughly wetted down, not just misted. Spraying should be done intermittently over the course of the day to prevent humidity build-up. 
5. Shade. Reducing direct sun exposure to cattle is beneficial. In feedyards, adequate shading can cut death losses in half. Increased feed efficiency and improved gain may also be seen when cattle have access to shade in pens during hot weather periods.

Early intervention of heat stress is critical during summer months. Remember feedlot cattle will start to feel the effects of heat sooner than humans. The sooner action is taken to reduce body heat, the more likely that action is to be effective.