How to Avoid Production Losses in Swine Due to Heat Stress

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Long, hot, humid summer days can result in heat stress in pig operations. A study released by Ohio State University in 2003 concluded that heat stress costs the U.S. pork industry approximately $300 million each year.

Although pigs are generally raised in facilities with a controlled environment, it is not always possible to avoid high temperatures within the barns. Temperatures above 23°C can have negative impacts on animal performance. In extreme cases, heat stress in pigs can lead to death loss. For both animal welfare and business reasons, it makes sense to take measures to reduce the impact of hot weather on pigs.

When and How Does Heat Stress Occur?

Heat stress occurs when the environmental temperature rises to a point where the animal is producing more heat from metabolism, or receiving more heat from its surroundings, than it is transferring from its body to its environment.

Heat stress is a concern with pigs because they do not have functional sweat glands to help them reduce body heat. They lose heat to their surrounding environment by conduction, thermal radiation, convection and evaporation to maintain their ideal core body temperature. If temperature and relative humidity are too high, pigs can no longer maintain their ideal body temperature.

Figure 1 shows a Heat Stress Index for grow-finish pigs, determined by temperature and relative humidity, that can be used to assess the risk to animals under various conditions.

Index with blue squares on the bottom, light yellow squares above it, beige squares above that and red squares at the top.  No heat stress is written on the blue squares. Heat stress alert is written on the yellow squares. Heat stress danger is written on the beige squares. Heat stress emergency is written on the red squares. Relative humidity is listed across the top starting at 40% on the left and increasing by 5% to 100% on the far right. Room temperature is listed on the left hand side starting at 21 on the bottom and increasing by 1 degree to 35 at the top.

Figure 1. Heat stress index for grow-finish pigs. Adapted from H. Xin and J. Harmon. 1998.

Text equivalent to Figure 1

Under heat stress conditions, the goal is to minimize heat transfer to the animal from the surroundings and maximize heat transfer from the animal to its environment. Recognizing the potential for heat stress, or that pigs are experiencing heat stress, is the first step in helping the animals cope with a hot, humid environment.

Signs of Heat Stress

  • evident discomfort or distress: pigs lying apart, body stretched out
  • manure patterns change: pen floors become wet and unclean
  • increased water consumption
  • noticeable decrease in pen activity: slowness and lethargy
  • muscle trembling
  • rapid fall in feed consumption with reduced weight gains
  • very high respiration rate (panting)

Coping with Heat Stress

Pigs will try to increase heat dissipation and decrease body heat production. To support this:

  • Make sure pigs have unrestricted access to a good supply of clean drinking water.
  • Install a timed water sprinkler or mister system triggered by room temperature for group housed pigs (sows, grow-finish). Sprinklers should activate for 1-2 min. every 20-30 min. to allow moisture to evaporate from the pigs’ skin before starting the process again. Larger water droplets work better than a fine mist.
  • Install a drip cooling system or sow cooling pads for individually housed sows.
  • Ensure proper ventilation rates for the size of room and the weight of the pigs (Table 1).
  • Do not overcrowd pigs. Provide enough pen space so that all the pigs can lie down without touching each other and still access feeders, waterers and the dunging area without stepping on pen mates.
  • Work with your nutritionist to reformulate more nutrient-dense diets during hot weather.
  • When pigs are fed at set time points, alter the time of day in which the bulk of feed is offered. Providing the majority of feed during cooler hours will help reduce decreases in feed intake.

Table 1. OMAFRA ventilation rate guidelines

Type of Animal
Ventilation Rate per Animal
Cold Weather
Warm Weathera
Breeding/gestating sow
10 CFM
200 CFM
Farrowing sow with litter
15 CFM
400 CFM
Nursery pigs, 4-25 kg
1.0-3.0b CFM
15-35c CFM
Grower pigs, 25-60 kg
4.0-6.0 CFM
50-70 CFM
Finishing pigs, 60-120 kg
6.0-8.0 CFM
70-90 CFM

a Summer ventilation rate for large pigs may have to be increased to 1 air change/min. during hot summer weather.
b For reasonably good air quality, this minimum winter ventilation rate may have to be increased to ensure at least 3-4 room air changes/hr.
c Limit the maximum number of summer air changes to 1/min. for sensitive livestock.

Source: Ventilation for Livestock and Poultry Facilities, Pub 833, OMAFRA.

It is important to recognize when temperature and humidity can increase the risk of heat stress in pigs. By recognizing when pigs are experiencing heat stress, and knowing how to help them cope, we can prevent or reduce production losses during periods of hot weather.

Be Prepared

The weather cannot be controlled. Plan ahead and have strategies in place to deal with hot weather when it happens.

Death loss due to heat stress is most often attributed to power outages in hog barns when there is no alternate power source or power loss back-up plan. Test your alternate power generation and power outage alarms monthly for fan-operated barns. Check panic doors/drop curtain releases for naturally ventilated barns. Heat build-up in non-ventilated barns can cause fatalities in all seasons.


Transport during any season can cause heat stress in pigs and may result in death loss. Producers can mitigate this in the following ways:

  • Load animals in groups of less than five.
  • Adjust transport to early morning or at night during the summer.
  • Load fewer pigs per load on hot, humid days, following Ontario Pork’s Loading Density Guidelines.
  • Provide wet shavings when the temperature is over 15°C; do not use straw.
  • Mist or spray pigs with water prior to loading, when the temperature is over 27°C.
  • Do not pour large amounts of cold water onto an overheated pig.
  • Load and unload promptly to avoid heat build-up.

OMAFRA’S Heat Stress in Livestock and Poultry App

Enter temperature and relative humidity on your Blackberry or Android smartphone to estimate heat stress risks quickly and easily with the Heat Stress in Livestock and Poultry App. The app also suggests steps to take to reduce heat stress to maintain feed intake and productivity.

Download the free Heat Stress in Livestock and Poultry App from Blackberry World or Google Play. The app features English, French and Spanish options.


  • National Pork Board TQA program
  • Loading Density Guidelines. Under “Industry – Resources -Transportation.”
  • St-Pierre, N.R., B. Cobanov and G. Schnitkey. 2003. Economic Losses from Heat Stress by U.S. Livestock Industries. J. Dairy Sci. 86:E52-E77.
  • University of Minnesota PorkBridge Educational Series
  • Ventilation for Livestock and Poultry Facilities. Pub 833, OMAFRA.
  • Xin, H., and J. Harmon. 1998. Livestock Industry Facilities and Environment: Heat Stress Indices for Livestock. Iowa State University.

This factsheet was written by Jaydee Smith, Swine Specialist, OMAFRA, Ridgetown, and Laura Eastwood, Swine Specialist, OMAFRA, Stratford.

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