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Heat Stress Index Chart for Swine Producers

Monday, August 26, 2002

By Iowa State University - Due to the fact that the US National Weather Service (NWS) has cut back on information that they provide to radio stations on livestock heat stress, ISU has developed a heat stress index chart to aid swine producers in making management decisions based on the current weather situation.

The heat stress indices (HSI) combine the effects of both temperature and relative humidity, and classified as alert, danger, and emergency zones.

Because different animal species and humans have different sensitivities to temperature and relative humidity, the heat stress charts are thus unique of that particular species.

For example, compared to swine, cattle can tolerate much higher temperature at lower relative humidity. This difference arises from the fact that cattle exposed to hot temperature can dissipate their body heat more effectively by sweating, whereas swine or poultry do not have sweat glands. As temperature increases, thereby temperature difference between the environment and the animal narrows, more body heat has to be dissipated via the so-called evaporative heat loss mode.

The natural capability of sweating by cattle gives them an edge over swine and poultry to rid of their body heat in the hot and dry conditions. By the same token, increase in relative humidity during hot weather will put cattle under stress much faster than for pigs or chickens.

The following figure is the one relevant to swine.

Heat Index Zone Classifications

The following lists the recommended management actions for the three HSI categories.

Prepare to take necessary cooling measures; increase ventilation rate; turn on cooling fans where applicable; monitor animal behavior for signs of heat stress such as panting or open mouth; make plenty of drinking water available.

Apply additional cooling by spraying or misting the animals with water (make sure that there is plenty of air movement during this phase); start evaporative cooling pads and tunnel ventilation where applicable; When possible, move air over the animals at a velocity of 250-300 ft per minute or 2.8-3.4 MPH for swine. Flush the water lines periodically.  Closely monitor the animals.                                          

Avoid transporting market weight animals. In addition to measures listed for the Danger category, withdraw feed during the hottest part of the day; reduce light level in light-controlled houses to reduce animal activity and thus heat production.     

The Heat Stress Index charts for other species can be found at:

Source: Iowa State University - August 2002

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