Typical ventilation controllers turn devices (heaters or fans) on and off in response to temperature changes as detected by one or more temperature probes suspended in the animal facility. Current ventilation control strategies as implemented by almost all ventilation controllers installed in production facilities contribute to temperature variation.
For example, the typical staging of fans in a grow-finish facility would be stage 1 operates from 50% minimum speed at controller set point to 100% minimum at 2F above set point (bandwidth). At 2.5F above set point stage 2 comes on at 50% and ramps to 100% at 4F above set point. Stage 3 comes on at 5F above set point, etc. Which fan stage operates is a function of heat production by the pig (pig weight dependent), heat loss/gain from the facility structure (insulation levels and air leaks) and ambient temperature (amount of heat that can be added to each unit of incoming ventilation air). This means temperatures vary within the pig facility over a 24 hour period, sometimes by quite a bit.
There is a new generation of ventilation controllers coming on the market from several suppliers that change how fans are staged in response to the call for heat removal from a facility. Rather than turning fans on/off in response to incremental rises in temperature, the new controllers turn fans on/off in an attempt to maintain a constant temperature in the facility using sophisticated computer logic.
This new controller logic raises the question – does the pig grow better with a constant air temperature such as can be maintained with the newer controller logic or does it by nature do better when temperatures fluctuate?
Studies in the 1970’s and 80’s determined that the pig’s thermal requirements are not constant. There are a variety of reasons for this, including a circadian rhythm for core body temperature (thought to be associated with pig activity at meals).
This 24 hour circadian rhythm in thermal requirement is confounded with pig care activities – as an industry we typically do chores the same time each day in our production facilities, in effect setting the biological clock for the growing pigs in our care.
In general, when given the opportunity to select temperatures in a group housed situation, pigs almost always select cooler nighttime temperatures than daytime temperatures. For nursery aged pigs the selected nighttime temperature is most often 7-10F cooler than the daytime selected temperature. The timing of this temperature selection coincides with relative rates of heat loss. That is, pigs have been demonstrated to have higher rates of heat loss during the day (possibly due to more activity) than during the night.
In almost every reported experiment that I’ve reviewed, pigs begin selecting for cooler temperatures around 5-7pm and begin calling for warmer temperatures around 5am. In almost every instance with nursery pigs, this selected temperature range is 7-10F. What this means is that when pigs are given a chance to self-select the temperature of their environment, they choose cooler night time temperatures than day time temperatures.
At the same time, while pigs demonstrate a preference for a gradual change in temperatures from day to night and night to day, the data suggests that repeated temperature fluctuations of 5-7F within one hour adversely impact pig performance.
Overall, the data suggest that the pig prefers gradual changes in temperature from day to night but does not react well when the temperature changes are rapid and repeated. If the new generation of ventilation controllers work as designed so that temperature variation is minimized, will it result in improved pig performance versus current controllers?
The jury is still out on this one.