Dana Zook (column mug)ENE

Without much warning, a cool wet spring gave way to the heat and humidity of summer. These high temperatures are great for getting wheat harvested but they can be hard on livestock.

All levels of heat stress will impact animal performance to some degree, and they can be realized in the form of decreased weight gain, reduced reproductive efficiency, altered animal health and behavior. Heat is a reality, but there are things that can be done to prevent severe heat stress in livestock. This article will focus on cattle, but the information will be applicable to most other livestock species.

First let’s discuss the basics of heat stress. Heat stress is a condition where an animal’s core body temperature rises beyond a level that they can manage with heat dissipation efforts. An animal’s upper critical temperature (where heat stress is initiated) will vary from one animal to the next and is dependent on breed, body condition, production stage, fly pressure, hide color and condition of hair coat. Remember that livestock do not only feel the impact of ambient temperature, but also the affects of humidity and wind speed. These hot, humid days with little wind are the perfect recipe for heat stress. During high temperatures, cattle will adapt both physiologically and behaviorally to reduce their heat load and some natural behavior will decrease in favor of heat dissipation efforts. Some natural behaviors that are negatively impacted are grazing, feed intake, grooming and calf care.

So how do cattle cope during the heat? One of the best methods to cool down is to seek shade. Animals without access to shade will orient their bodies to reduce sun exposure and stand rather than lie down to increase cooling. Sweating also is key to evaporative cooling but cattle’s ability to do so is much less than that of humans and horses. In addition, feed intake may go down during periods of high temperatures to reduce the amount of heat produced from digestive processes. Panting behavior also is common during the high temperatures, but animals in more severe stages of heat stress will slobber, lack coordination and will be hard to move. Producers should make all effort to minimize any stress for these animals if they are to overcome this state of heat exhaustion. Heat stress also may cause compromised immune function to a certain degree causing animals to be more at risk for disease.

Temperatures above 90 degrees are a reality in Oklahoma, so what can producers do to ease the impact on livestock? During hot temperatures (and all situations, really), the most important resource for all animals is a clean source of drinking water. Multiple watering locations are encouraged, be that a natural water source such as a pond or automatic water. Make sure there is enough watering space and volume of water during times of heat stress. A beef cow’s happy spot on the temperature scale is approximately 65 degrees, and a good rule of thumb is that every 10 degrees above this level will increase water needs by 1 gallon. For example, a 1,300-pound lactating cow will require 15 gallons of water on a 65 degree day and 18 gallons of water on a 90 degree day.

Shade is one of the most effective ways to decrease overall heat load on cattle. Shade structures should be constructed at least 13 feet high to produce functional shading and maintain airflow. Shade reduces solar radiation and ground temperature in the exposed area. Remember, not all shade is created equal. Airflow and moisture management in the shade must be maintained. Don’t forget fly control during heat also. Cattle exposed to intense fly pressure will have increased body temperature, which adds to the stress.

Control flies with sprays, fly tags, pour-ons and insect growth regulators (IGR) to reduce this aspect of summer stress. Finally, if cattle processing must be done during the heat of the summer, plan to have a majority of cattle worked by 8 a.m.

Take these tips to mitigate heat stress this summer in your cattle herd. Don’t forget to keep the humans in your herd hydrated too. For more information on managing heat stress in livestock, contact your local county OSU Extension office.

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Zook is Oklahoma Cooperative Extension Service northwest area livestock specialist.

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