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Due to the fact that the National Weather Service (NWS) has cut back on information that they provide to radio stations on livestock heat
stress, the following heat stress index charts have been developed to aid producers in making management decisions in livestock and poultry production. The heat stress indices (HIS) 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. Table 1 lists the recommended management measures
for each of the three HSI categories.
Table 1. Livestock/poultry heat stress index category and recommended management actions.
Recommended Management Actions
Prepared 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; setup cooling sheds for cattle if possible.
Danger 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/cattle and 350 to 400 ft per minute or 4.0-4.5 MPH
for poultry. Flush the water lines periodically. Closely
monitor the animals.
Emergency 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 STRESS INDEX FOR CATTLE HEAT STRESS INDEX FOR SWINE
HEAT STRESS INDEX FOR LAYING HENS
HEAT STRESS INDEX FOR 15-WK HEN TURKEY
HEAT STRESS INDEX FOR HUMANS
Further questions regarding application of the charts may be directed to Drs. Hongwei Xin
(515-294-9778) and Jay Harmon (515-294-0554), Department of Agricultural and Biosystems engineering, Iowa State University.
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