Fine-tune ventilation, evaporation to combat heat stress in pigs

Without the ability to sweat, pigs must rely on conduction, convection, radiation, and respiration/evaporation to remove body heat. Forcing air across a wet pig — the process of convection and evaporation — helps them keep their cool.

Producers combatting heat stress have two cooling-system options: direct and indirect.

“Direct cooling systems rely on placing a film of liquid water on the back of the pig along with about 400 ft/min (2.03 m/s) of air speed to increase evaporation and promote cooling of the animal,” explains Steven Hoff, PE, professor of agricultural and biosystems engineering at Iowa State University.

“Indirect cooling relies on evaporative pad systems that cool the air before it reaches the pig,” he adds.

Know the signs of heat stress

One of the first signs of heat stress in a finishing barn is open-mouth breathing or panting at a rate of 50 breaths per minute or more under resting conditions. This rapid mouth breathing helps cool the deep body temperature by evaporating water from the surfaces of the lungs and respiratory tract.

As the pig’s body temperature increases, blood leaves the viscera and rushes to the skin in an attempt to dissipate heat. The result is animals sprawling on the floor to increase skin contact with the cooler floor surface.

Reducing stocking rates during the summer months gives pigs additional room to spread out. Finishing pigs 150 pounds (68 kg) to market weight should be given more than the standard 8 to 9 square feet (.74-.84 m²).¹

Increasing pig comfort

Sprinklers and drip coolers help reduce the animal’s body heat through evaporation. Sprinkling water over a 1- to 2-minute interval every 20 to 30 minutes provides enough moisture to wet the pig and enough time for it to evaporate off the skin before wetting again. Individual barn and pen arrangements dictate cycling of sprinklers from selected sprinkler nozzles to attain this coverage.

“The water must wet the pig to remove body heat and create a cooling effect,” Hoff stresses. “Misting can evaporate before reaching the animal.”

A continuous fine mist can also increase the humidity level in the barn without encouraging evaporation.

“The goal is to let pigs nearly dry between cycles and then rewet,” he adds.

Repositioning stir fans increases the efficiency of the evaporative process for a larger number of animals. Hoff explains a correctly angled stir fan that provides air to the back of the animals at about 400 ft/min (2.03 m/s) will treat an area of 30 to 40 feet. This is roughly a 10-fold increase in air velocity over speeds needed in pens during the winter months.

Hoff encourages swine producers to fine-tune each room of their facilities based on, for example, the size of pigs or solar load.

“There is no rule of thumb for starting fans and sprinklers to prevent heat stress,” Hoff points out. “The swine producer’s best tool for managing their facility is the power of observation and knowing his or her animals.”

 He urges producers to complete a thorough check of all ventilation components. Temperature sensors, fans, air inlets, drip coolers, and sprinklers need to be cleaned and working properly to avoid loss of livestock due to overheating.

¹ Souza L. How to reduce heat stress in your pigs. University of Minnesota Extension. Available at https://www.porkbusiness.com/article/how-reduce-heat-stress-your-pigs.