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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.



Category   Recommended Management Actions                                

Alert       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 production.                                              

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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