What is heat load?
All animals have a need to maintain core body temperature within a small range so that body cells and tissues can function optimally. For humans the range is 36.5 to 37.5°C, for cattle it’s in the range of 37.9 – 40.2oC depending on the cattle breed/genotype. This range needs to be maintained even when additional heat is added to the system. For animals in a feedlot, the conversion of food into energy (called metabolic heat) is the major source of heat being added to the system. A problem occurs if heat accumulates beyond the animal's ability to dissipate it to the environment. In this situation, an animal will start to store heat, which we call a heat load.
It is important to understand the basic heat balance for animals in a feedlot to ensure appropriate mitigation strategies are implemented to reduce the risk of a heat load event. The mechanisms associated with heat gain and loss in cattle are illustrated below.
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It is important to note that for cattle evaporation is the major mechanism they use to dissipate heat. When the air is already holding a lot of moisture the rate of evaporation from cattle panting is reduced. Therefore cattle are more likely to gain heat if the conditions are humid.