– Dr. Katie VanValin, Assistant Extension Professor, University of Kentucky
Heat stress is a problem that can affect cattle throughout the United States. However, in Kentucky and across the southeast cattle are at risk for experiencing more frequent and severe heat stress events than in other regions of the country. Heat stress occurs when cattle cannot dissipate or get rid of excess heat, and there are a multitude of factors that can impact how susceptible an individual animal is to heat stress. These factors include things such as breed, stage of production, age, and hair coat color which can make it difficult to predict an animal’s susceptibility to heat stress. Heat stress results in decreased growth and reproductive performance and in severe cases even death; thus, it is not a problem that should be overlooked.
Cattle can be particularly susceptible to heat stress compared to other species because they are unable to sweat effectively, which means they rely on respiration to try and dissipate heat. Thus, a common sign that cattle are experiencing heat stress is excessive panting and increased respiratory rate. Furthermore, the cattle GI tract features the rumen, a large fermentation vat. While the rumen is what allows cattle to take human inedible protein and convert it to human edible protein in the form of beef or milk, this process also generates heat that the animal must dissipate. It is thought that this might be partially responsible for the decreased feed intake observed in cattle exhibiting heat stress.
Grazing endophyte infected fescue can also lead to more severe heat stress compared to grazing other forages. The endophyte produces ergot alkaloids resulting in decreased blood flow to peripheral tissues and the skin making it more difficult for cattle to dissipate heat. Additionally, the rough or retained winter haircoat can also make it more difficult for cattle to dissipate heat. This means cattle consuming endophyte infected fescue may have to work harder than cattle consuming other forages to regulate their body temperature, and this increased effort can lead to increased maintenance energy requirements.
Unfortunately heat stress is a complicated issue, and there is not a magic number on the thermometer to pinpoint when cattle will experience heat stress. In addition to animal factors, there are a number of environmental factors that affect the likelihood that cattle will experience heat stress. These factors include things such as temperature, wind speed, humidity, and solar radiation. Fortunately, some weather services such as the UK Ag Weather Center use those individual environmental factors to produce a heat stress forecast which categorizes the current conditions as either normal, alert, danger, or emergency.
While we can’t control the weather, there are a number of steps that can be taken to help alleviate heat stress in cattle.
- Watch the weather before working or moving cattle – Observe the weather as well as livestock heat stress forecasts and avoid working or moving cattle during times of excessive heat or when heat stress forecasts are elevated. It is best to work cattle in the early morning hours during hot summer months. Avoid moving or working cattle in the evening, because this is the time that cattle are working to dissipate heat accrued during the day.
- Shade – Solar radiation plays an important role in an animal’s susceptibility to and ability to cope with heat stress. Ensure cattle have access to shade, each animal requires 20-40 square feet of shade to be comfortable. Shade is especially important to cattle housed in feedlots or dry lots as the surfaces in these facilities can give off more heat compared to pasture conditions. If using an artificial shade structure, ensure that it is at least 8 feet tall to allow ample air movement underneath the structure.
- Ventilation – If cattle are housed in confinement such as an enclosed barn or building, fans can be used to improve circulation of air throughout the building. Ventilation should be an important part of any facility remodeling or design.
- Water – During periods of excessive heat cattle can consume over 25 gallons of water per head per day. If using a stock tank, ensure that there is enough area for multiple animals to drink at once. Ensure that water flow rates are fast enough to keep up with increased water intake. Regardless of water source ensure that the water provided is clean and cool. When water temperature increase above 80℉ intakes can be decreased, so ensure water lines are not exposed to direct sunlight. Furthermore, intake can be decreased if the water source is dirty, so ensure a clean water source free of algae.
- Mineral – Minerals are a required nutrient and a complete free choice mineral should be provided for cattle on pasture 365 days of the year. With increased water intake associated with heat stress, urination will also increase and along with-it excretion of certain minerals. Provide mineral in a location where cattle will readily consume it, as intake is key to any mineral program!
- Feeding time – For cattle on feed, heat production will peak 4-6 hours after feeding. So, cattle fed in the morning will have peak heat production from feed intake during the hottest part of the day. Thus, cattle should receive ~70% of their feed 2-4 hours after the hottest part of the day.
- Decrease dietary energy – Again for cattle on feed, research has shown that decreasing dietary energy can lower heat load for cattle during extreme heat. Work with a nutritionist before making dietary changes!
- Pasture selection – If possible, avoid grazing endophyte infected fescue pastures during periods of extreme heat. This may not be feasible for all operations. Cattle should be on pastures that provide ample shade during the hottest parts of the day and allow for easy access to the water source from the shaded locations.
- Fly control – When cattle are battling with flies, they tend to cluster together making it difficult to effectively dissipate heat. Also, fly avoidance behaviors exhibited by cattle, such as foot stomping, tail switching, and head movements require energy and can further exacerbate heat stress.
- Take care of yourself- Last but certainly not least risks to human health are often overlooked when discussing heat stress on livestock operations. The most important part of any beef cattle operation are the people behind it. So, take precautions and be able to recognize the signs of heat exhaustion and heat stroke!