Articles on forages, animals, and grazing systems
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Extension Forage Specialist
University of Kentucky
Phone: (859) 257-3358
Fax: (859) 323-1952
Heat stress in livestock can start as early as May in Kentucky. Dairy cows can see decreases in milk production as a result of heat stress at temperatures as low as 72⁰ F at a relative humidity of 45% while beef cattle begin to show signs of heat stress at 77⁰ F. Heat stress has a large impact on animal health and can significantly decrease animal performance.
Heat stress has many negative effects on livestock that can significantly decrease animal performance and production. The reproductive system is affected in multiple ways. Cows often show decreased conception rates, decreased duration and intensity of estrus, decreased calf birth weight, and increased early embryo mortality when experiencing heat stress. Milk production and gains are also considerably decreased. Heat stressed cattle spend less time grazing and consume less feed which partially explains the observed reduction in performance. Any and all operations can be negatively impacted by heat stress. It is important to look ahead in early spring and prepare to reduce heat stress for the grazing season.
Allowing cattle access to shade and cool water at all times is vital. Cattle grazing endophyte infected tall fescue can experience more intense heat stress. Blood flow is reduced which reduces the animal’s ability to dissipate body heat. The rough hair coat and failure to shed winter coats are common symptoms of fescue toxicity. Body temperature and respiration rates are increased. Taking steps to reduce fescue toxicity, such as taking livestock off fescue infected fields during the hot months, can also help reduce the severity of heat stress in the herd. Supplying shade and cool water is necessary to reduce heat stress. Another option is to turn cattle out only at night onto pastures without shade. Reducing heat stress in the herd will increase animal performance and overall profitability. For more information on shade options for grazing cattle see http://www.bae.uky.edu/publications/AENs/AEN-99.pdf.