Does the pig do better with constant vs varying temperatures?

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.

4 thoughts on “Does the pig do better with constant vs varying temperatures?

  1. Thanks for a great literature review on temperature variation. Now the next step based on the literature and your personal knowledge, can you put together a matrix of ideal temperatures from day to night for various pig sizes. This information would form the basics for a great research project as well as assist the controller manufactures to design a new generation controller.

  2. Great comment Dick. The challenge – we really don’t know the upper and lower critical temperatures (thermal neutral range) for today’s genotypes and diets. The evidence is very clear that the heat output of growing pigs (and lactating sows) has increased due to higher rates of lean deposition and milk production. There is some recent literature suggesting today’s pigs are more sensitive to high temperatures but no data that I’m aware of on the issue of lower critical temperatures. Before one can put together a daily curve of fluctuating temperatures you need to know the boundries as a starting point. We also need more data on the rate of temperature variation. The pig chooses a gradual temperature change – how much ‘gradual’ do you program into a controller? Right now those using reduced nocturnal temperatures simply lower the furnace OFF temperature setting in the controller and the room cools in response to heat loss from the minimum ventilation fan and loss through the building surfaces – it is not driven down by turning on fans.

  3. Thanks Mike for listing the gaps in information which we do not know. Therefore we need research on thermal neutral temperatures for today’s genotypes as well as the ideal rate of temperature change during a 24 hr period. This research would be of great benefit to the pork industry and should be considered by the Pork Producers Council for funding. They would ask “what is this benefit?” And they should ask. From my experience I would suggest that reducing the stress on the pig by providing the correct environment, providing a proper diet, and using today’s genetics, the feed efficiency on a production system can be improved to 2 pounds of feed per pound of gain. When that FE is achieved, it would translate to profit for the producer.

  4. At some point we will talk about 2.0 feed conversions for wean-finish. I have seen individual boar data for grow-fin already under 1.9 lb of feed per lb of gain so the genetics are coming. As you rightly discuss, the challenge is getting the environmental limitations out of the way. Because of funding limitations, the public knowledge base to work from is decreasing, not expanding. More and more of the production research is now in private hands making access to information a future limit for many producers ability to compete successfully.

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