There are many factors that influence a particular animal’s response to heat stress. Factors can be grouped in four different areas. These areas are genetics, health, production status, and previous exposure to heat stress. Listed in the table below are the risk factors and the associated animal traits that will increase the animal's susceptibility to heat stress. Click on a risk factor to view more detailed information concerning that risk factor and associated traits.
Genetics: Genetic components include many different factors including breed, temperament, and color. Breeds, breed crosses, or composite breeds from cattle with historical origins in the tropics or subtropics tend to be more heat tolerant relative to those cattle of 100% European origin. Breeds originating on the subcontinent of India, Bos Indicus (referred to as Zebu) breeds such as the Gir, Nelore, Guzerat, Ongole, and Sindhi contributed heat tolerance to the American Brahman composite. The American Brahman has been used extensively in the Gulf coast regions of the United States in matings with European breeds to create populations better equipped to withstand the heat stress in this region. The ability to tolerate heat stress has also been recognized among Bos Taurus breeds that evolved in hot humid climates including the African breeds Tuli, Africandar, and the Bonsmara (collectively referred to as Sanga types) or from Criollo types (e.g., Romosinuano, Texas Longhorn) that evolved in the tropics of the New World from cattle that Spanish explorers brought to the Americas from Europe.
Color plays an important role in heat tolerance. Dark colors absorb more heat than light colors. As a result, a black animal will be more susceptible to heat stress than a white or tan animal.
It has recently been shown that temperament also plays a small role in heat tolerance. Animals that are calmer are more heat tolerant than animals that are more excitable.
Health: The current general health of the animal will influence its ability to withstand additional stress including heat stress. The effects of pneumonia are long lasting. An animal that has been treated for pneumonia at any time in its past has a higher risk of heat stress symptoms during hot weather than those animals that have not had the disease. Animals which have had pneumonia and have not been treated could be at even higher risk.
Previous Exposure: Cattle that have not been preconditioned to hot weather will have a greater stress response (higher breathing rate, higher body temperature). Cattle become preconditioned to heat stress when they have prior exposure to hot weather. Moving cattle from a cool region of the country to a hot environment can increase the animal’s susceptibility to heat stress.
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