Articles on forages, animals, and grazing systems
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Master Grazer Coordinator
804 W.P. Garrigus Building
University of Kentucky
Extension Forage Specialist
University of Kentucky
Phone: (859) 257-3358
Fax: (859) 323-1952
Heat stress in cattle is an issue that all Kentucky cattle farmers face during the summer months.
The high temperatures and humidity that are common to Kentucky are the main cause of heat stress. Other causes include direct radiation and low air movement. Endophyte infected fescue, which is found in the majority of Kentucky pastures, is another source as it increases body temperatures. Heat stress can significantly decrease performance of dairy and beef cattle.
Herd health is greatly impacted by heat stress. At temperatures as low as 77⁰ F cattle begin showing signs of heat stress. As relative humidity increases the temperature at which livestock begin experiencing heat stress decreases. Dairy cows can experience heat stress at 72⁰ at a relative humidity of 45%. At this point reproduction rate, gain, milk production, and overall health can be negatively affected. According to Dr. Jeff Lehmkuhler, UK extension beef cattle specialist, cows often show decreased conception rates, decreased duration and intensity of the estrus, decreased calf birth weight, and increased early life mortality. Cattle suffering from heat stress spend less time grazing and consume less feed which means lower gains, decreased milk production, and lower overall performance. Although it may not be possible to completely reverse the negative effects of heat stress, it is possible to lessen these effects by taking steps to provide cattle access to shade and cool water.
Providing shade is essential in order to reduce heat stress. Shade will intercept radiation from the sun and can reduce heat loads on cattle by up to 30%. Natural shade provided by trees is ideal but is difficult to provide in many situations. Providing artificial shade will also work well. Artificial shade can be a permanent or portable structure. There should be adequate amounts of shade to provide all livestock access. Issues with small shaded areas include soil compaction, soil erosion, and reduced manure distribution. Because of high hoof traffic, soil around a shade area often becomes compacted and bare. Manure accumulation and wet, muddy conditions can cause health problems in livestock as well as environmental problems such as nutrient pollution and water quality issues.
If portable shade is being used, regularly moving the shade can help reduce these problems. Turning livestock into pastures without shade during the night is a simple strategy to reduce heat stress.
High temperature and humidity conditions result in cattle drinking more water. Having cool drinking water available at all times is vital to maintaining performance. During hot days, a dairy cow producing 50 lbs. of milk can drink up to 30 gallons of water each day. Reduced water intake decreases feed intake. Milk production and gains are significantly cut back as water consumption decreases. Water location, temperature, and quality are equally important to factor into a watering system. In order to keep grazing distribution even, water should not be further than 800 feet from all areas of the paddock. Cattle will travel a maximum of ½ mile to water sources. Considering amount of total dissolved solids or sulfates in water as well as algae contamination is essential to providing high quality water to livestock. Water temperature should be below the body temperature of the cattle. Providing cool, clean water to cattle at all times is important to maximized health and performance.
During these hot summer months, heat stress is a common problem that farmers face. In order to maintain livestock health and performance it is vital to attempt to reduce heat stress. Providing access to shade and cool, clean water can greatly reduce these issues and help keep herds healthy.