By Lexi Roof and Suzanne Leonard, North Carolina State University

Combating heat stress in an economically friendly manner is a key challenge that swine producers face, especially in warm climates like North Carolina. Heat stress in swine can lead to negative production effects, including reduced growth rates, health problems and a decrease in reproductive performance. Pigs have limited numbers of functional sweat glands and unlike humans do not cool themselves effectively, making supplementary cooling methods necessary.

With the exceptions of natural ventilation, mechanical ventilation and in-floor cooling, the other methods presented here rely on the evaporation of water to either cool the pig directly or the air indirectly. Direct cooling uses water present on the pig’s surface, such as water from sprinklers, and removes heat from the pig by evaporating the moisture. With indirect cooling moisture is added to the air, which increases its water vapor content and decreases the air temperature. Colder air can remove more heat from the pig than warm air, thus cooling the pig.

These evaporative methods are most effective when the outdoor air has low humidity and can absorb (evaporate) more water vapor. If the air is full of water vapor (that is, high relative humidity), there will be nowhere for the extra water to go and it can accumulate on surfaces.

Ventilation is the first line of defense against heat stress, and selecting additional cooling methods to be used in conjunction with your ventilation system can increase cooling effectiveness and efficiency.

Ventilation cooling methods

Natural ventilation

Natural ventilation is a low-cost option to combat heat stress in swine. Local wind patterns and the orientation of the barn affect how much wind can flow through the barn. Any obstructions to air flow, including outside and inside the barn, can decrease the effectiveness of natural ventilation. Ventilation inlets and outlets can be manually or automatically controlled and adjusted to maximize the airflow in warm conditions and stir fans can be added to further remove heat and moisture from the pigs. Although this is an attractive method of cooling because of the low costs and minimal, if any, electrical components, it may not be an efficient cooling method on its own for areas with extreme temperatures or low windspeeds.

Mechanical ventilation

There are several different methods of mechanical ventilation that are used in swine production, namely negative pressure, positive pressure and neutral pressure. In general, mechanical ventilation operates using fans and inlet controls to replace the hot air in the barn with cooler air from outside the barn. The fresh-air distribution system also removes humidity from the barn air and increases the air speed around the pig. An automated control system is used to manage and control the ventilation system components. Most mechanical ventilation systems use tunnel ventilation to cool pigs with airspeeds of 600-700 feet per minute at the tunnel inlet. Although these methods are highly adaptable and easily available due to the numerous products on the market, mechanical hardware and air inlet placement are very important to effectively control the environment. Further, large amounts of electricity are typically consumed when using mechanical ventilation.

Direct cooling methods

Sprinklers

Sprinklers are a type of direct cooling method that briefly wet the pigs with large water droplets. Then, the sprinklers turn off and water is allowed to evaporate as the evaporation process removes heat from the pig. As barn temperature increases, most sprinkler systems are able to adjust the water application and evaporation time. Although sprinklers are an effective method when used correctly, sprinklers can become counterproductive if not used properly. For example, if the sprinklers are left on for long periods of time, the relative humidity in the barn will rise and the effectiveness of the cooling system will decrease. A general rule of thumb is to turn the sprinklers on for 2-4 minutes to thoroughly wet the pigs, then allow enough time for the pigs to thoroughly dry before wetting the pigs again. In dry climates, this could take 15-20 minutes, but in more humid areas it could take up to an hour.

In-floor cooling

In-floor cooling is one of the more expensive cooling methods used in swine production. In-floor cooling is typically accomplished using water pipes embedded in the flooring. Cool water is circulated through the pipes to remove heat from the pigs laying on the flooring. A water chiller is often used to cool the water again before it is recirculated. Some cooling systems are sold as mats that can be placed on top of existing flooring, rather than pipes embedded in the floor itself.

Indirect cooling methods

Foggers

Foggers operate by releasing small water droplets into the air at a high pressure, which become water vapor. The air increases in water vapor content, lowering the temperature of the air. As such, they are not a good option for very humid climates as the water vapor content of the air cannot be effectively increased. If the water produced by the foggers is not given time to dissipate, there will be too much water vapor in the air and this can lead to excess wetting of the pigs and other barn surfaces.

Evaporative cooling pads

Evaporative cooling pads, sometimes called cool cells, evaporate water by using the heat that is already in the air. Outside air with high temperature and low humidity is passed through a cardboard or plastic pad coated in water. This forces the air to evaporate some of the water, increasing the air’s water vapor (humidity) content and reducing its temperature. Evaporative cooling pads work best with high temperature, low humidity air and therefore are generally most effective in the hottest part of the day. In dry climates they can decrease the air temperature by up to 12°F. It is recommended to let the pads thoroughly dry each night to reduce growth of mold and algae. Cooling pads require regular cleaning and treatment, as they can become clogged with dust, dirt, and mineral build-up from hard water sources. With proper maintenance, the cardboard pads typically last 3-5 years before needing to be replaced.

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