Combating swine heat stress in an economically viable manner is a key challenge for producers, especially in places with 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 a limited number of functional sweat glands and, unlike humans, cannot cool themselves effectively, making supplementary cooling methods necessary.

Ventilation is the first line of defense against swine heat stress. Additional cooling strategies can be used with ventilation systems to increase cooling effectiveness and efficiency. With the exception of natural ventilation, mechanical ventilation, and in-floor cooling, the methods presented here rely on water evaporation to either directly cool the pigs or the air around them. Direct evaporative cooling uses moisture on the pig’s surface (such as water added by 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. Evaporative methods are most effective when the outdoor air has low humidity and can absorb (evaporate) more water vapor. If the air is already full of water vapor (that is, having high relative humidity), the extra water has nowhere to go and can accumulate on surfaces.

Table 1 provides a summary of cooling methods, advantages and disadvantages of each, and relative purchase costs, water usage, and electricity usage.

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, whether outside or 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 during warm conditions Adding stir fans can further remove heat and moisture from the pigs. Although natural ventilation is desirable because of the low costs and minimal, if any, electrical components, it may not be an efficient cooling method on its own in areas with extreme temperatures or low wind speeds.

Mechanical Ventilation

Several methods of mechanical ventilation are used in swine production, namely negative pressure, positive pressure, and neutral pressure. Typically, mechanical ventilation consists of 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 air speed around the pig. Automated control systems are used to manage and control the ventilation system components. Most mechanical ventilation systems use tunnel ventilation to cool pigs with airspeeds of 600 to 700 feet per minute at the tunnel inlet. Although mechanical ventilation methods are highly adaptable and readily available due to the numerous products on the market, it is critical to properly place mechanical hardware and air inlets to effectively control the environment. Further, mechanical ventilation typically consumes large amounts of electricity.

Sprinklers

Sprinklers are a type of direct cooling method that briefly wets the pigs with large water droplets; then the sprinklers are turned 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 automatically adjust the water application and evaporation time. Sprinklers are effective but can become counterproductive if not used correctly. For example, if sprinklers are left on too long, 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 two to four minutes to thoroughly wet the pigs, then allow enough time for the pigs to dry thoroughly before wetting them again. In arid climates, drying can take 15 to 20 minutes, but in more humid areas, it can 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 lying on the flooring. A water chiller is often used to cool the water before it is recirculated. Some floor cooling systems are sold as mats that can be placed on top of existing flooring as an alternative to pipes embedded in the floor.

Foggers

Foggers operate by releasing small water droplets into the air at a high pressure, which become water vapor. The water vapor content in the air increases, lowering the temperature of the air. As such, foggers are not a good option for very humid climates because 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, which can lead to excess wetting of the pigs and 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 that is high in temperature and low in humidity is passed through a cardboard or plastic pad coated in water—forcing 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 arid climates, evaporative cooling pads can decrease the air temperature in the barn by as much as 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 buildup from hard water. With proper maintenance, cardboard pads typically last three to five years.

*Relative purchase cost of equipment and systems ↲

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