While the time and effort placed on winterizing hog facilities is well spent, from an economic standpoint, there are probably more reasons to prepare barns for the summer’s heat.
An estimate of the economic loss from heat stress for various U.S. livestock industries, conducted by Norm R. St-Pierre and associates at Ohio State University in 2003, showed the average annual loss due to heat stress was costing the pork industry about $300 million.
St-Pierre’s study was based on historical (68 to 129 years) weather data and included losses in growth rate in market hogs as well as reproduction losses in breeding animals (gilts, sows and boars). In most of the United States, average temperatures have been trending upward, so losses associated with heat stress will likely increase in the future.
In 2000, E.M. Lucas, Universidade de Evora, Portugal, documented that hot temperatures severely affected the performance of pig production, especially during longer and more intense heat stress periods, yet another trend that climatologists foresee.
Another potential economic loss, documented in a study by N.G. Gregory, Royal Veterinary College in the United Kingdom, linked heat exposure during housing and transportation of hogs to market to a negative impact on meat quality.
As winter temperatures begin to moderate, now is the best time to think about “summerizing” your pig barns.
Reducing Heat Stress
Well-insulated pig buildings with R-values of at least 15 in walls, 25 in ceilings and 8 in exposed roofs not only helps keep heat inside a building during cold weather, it also prevents heat from entering the barn during warm/hot weather and provides cooler inside surface temperatures for the pigs.
For totally mechanically ventilated barns, make sure exhaust fans are operating properly. Monthly fan maintenance includes checking for hot surface temperatures on electric fan motors with an infrared thermometer, cleaning and lubricating (graphite) fan shutters and tightening belts on belt-driven fans. Mechanically ventilated barns need to reach their designed maximum (summer) airflow rate through the exhaust fans.
To operate effectively, mechanically ventilated barns cannot have large, unplanned openings (leaks), such as open walk-in doors or open windows, since the building must have sufficient static or negative pressure to ensure enough air inlet velocity to reach pigs in pens or stalls.
A static pressure of 1/10 in. of water gauge (manometer) is the target level for a barn during the summer when all exhaust fans are operating. This will produce inlet air speeds of approximately 10 mph, which will provide excellent barn air mixing and assist in cooling the pigs.
In naturally ventilated buildings, outside winds determine the air exchange rate, so curtains or vent doors need to open fully during hot spells. Check for any large obstructions near these naturally ventilated facilities, such as trees or other buildings, that can block prevailing winds from reaching the barn’s sidewall openings.
Although circulation fans do not provide air exchange for a barn, they are helpful in either naturally ventilated or mechanically ventilated buildings, since they provide air movement over the animals. Circulation fans should be tilted downward about 15° from the vertical position to expose pigs to the fan’s air streams (Figure 1).
A well-designed, fully operational evaporative cooling system is probably the most important housing component to relieve heat stress in pigs. This system could include drippers in farrowing and stall gestation barns. Make sure drippers are positioned properly in a farrowing crate so water drips between the sow’s front shoulders.
Sprinkler systems and evaporative cooling pads work well in group sow housing or grow-finish barns. Sprinklers should spray large droplets of water to wet the pigs as quickly as possible and then shut off. Typically, sprinklers are set to run 1-2 minutes out of 10, so the water can evaporate and cool the pigs (Figure 2). Evaporative cooling pads require regular maintenance to make sure water is moving down through the full pad height to maximize its cooling potential.
Critical Core Temperature
Pigs, like people, are homothermic. That is, they need to maintain a constant core body temperature (about 102°F).
Pigs function normally when they are in their thermal-neutral zone (Figure 3). The thermal-neutral zone varies with the age and size of pigs and the effective temperature the pigs “feel,” which is affected by air movement, presence of bedding, humidity and surface temperatures.
When pigs experience an effective temperature below their thermal-neutral zone, they will increase feed intake and perform other activities to help retain heat in an effort to maintain their core body temperature.
When pigs experience temperatures above their thermal-neutral zone, they try to shed heat through behaviors such as reducing feed intake, drinking more water and, eventually, starting to pant. Unlike humans, pigs do not sweat. Their panting is a respiratory response to rid their bodies of excess heat.
The upper critical temperature, the vertical red line at right in Figure 3, is the threshold when pigs become uncomfortable and start reacting to heat stress. Heat stress is a gradual process that begins with small impacts on feed intake and growth rate, but can escalate to very serious and life- threatening consequences.
Preventing Heat Stress
Special temperature-humidity index (THI) charts (Figure 4 on page 11) have been developed to alert producers that their livestock are under various levels of heat stress. The three levels most commonly listed in these charts include:
Alert (THI 75 to 78),
Danger (THI 79 to 83), and
Emergency (THI at 84 or higher).
The THI charts are often just used to prevent mortalities and/or avoid serious heat stress rather than preventing heat stress in the first place.
The THI is determined from the barn’s temperature (vertical axis) and relative humidity (horizontal axis) in Figure 4. A new “app” for smartphones is also available at: http://cmer.uoguelph.ca/heatstressapp.
Typically, producers and barn managers are told to activate cooling systems when the THI reaches 75. However, as research at the University of Kentucky has shown (Figure 3), the three major performance parameters — feed intake, feed conversion and average daily gain — for 150-lb. finishing pigs are considerably less than optimum at a THI of 75, when, for example, environmental temperature is 80°F and relative humidity is 60%.
A THI of 70 (e.g., 75°F and 50% relative humidity) would be a better place to activate cooling systems such as sprinklers or evaporative pads.
Further consideration should be given to the newest genetic lines, which are leaner and grow faster, because they produce more heat than their 1990s counterparts. In other words, modern pigs may become heat stressed even before those shown in Figure 3.
From a practical management standpoint, it would be beneficial to reduce the pig density in grow-finish barns by topping off 5 to 10% of pigs during heat stress conditions.
Ventilation controllers in pig barns need a set-point temperature low enough to keep ahead of the heat build-up in the building and, thus, heat stress in the pigs.
In mechanically ventilated systems, all exhaust fans should be running before the upper critical temperature is reached. Likewise, in naturally ventilated barns, all sidewall curtains and/or vent doors should be fully open before the upper critical temperature is reached.
Shortly after the maximum air exchange in the barn is reached (e.g., 2°F above upper critical temperature), any circulation fans should begin to operate to provide air flow over the pigs. Finally, cooling systems such as sprinklers should also be activated when room temperatures climb an additional 2-3°F or roughly a THI of 70.
If the climate control system (ventilation/cooling system) for the barn is managed using this strategy, pigs will experience limited heat stress rather than try to be cooled down after they have already been exposed to moderate or severe heat stress conditions.
Future Cooling Systems
Nearly all of the existing cooling systems used in pig barns today are evaporative systems. Unfortunately, these systems are not effective when humidity or dew point temperatures are high. The evaporation of water, which is what removes the heat from the pig’s skin, is greatly reduced when dew point temperatures are high.
With the latest historical trends (past 10 years) and new climate change models predicting warmer and wetter conditions in the future, some non-evaporative cooling systems are being evaluated for use in pig barns. These alternatives include floor cooling in farrowing crates, gestation stalls and solid floors in partially slotted, grow-finish barns. Mechanical air conditioning, now only used in boar studs, is being considered to provide zone cooling of sows in farrowing rooms and some special sow and finishing hog barns to control heat stress and maintain growth and reproductive performance when the weather heats up.