As I write this week’s blog, the air temperature is 42 F with wind gusts from the NW up to 30 mph. However, by this weekend temperatures in the Mankato, MN area are predicted to be in the upper 70’s.

These changing weather conditions are a challenge for ventilation systems. As air temperatures rise, ventilation systems need to move an increasing amount of air to remove the same amount of heat produced by growing pigs. Readers of this blog who have tunnel ventilated barns can readily observe this point. Tunnel ventilated finishing facilities often go into tunnel ventilation mode (meaning they need more than 45-50 cfm/pig to maintain inside conditions) when pigs are nearing market weight and outside temperatures are in the mid to upper 50’s.

This need for heat relief in late April and early May always seems to catch producers unprepared. Many don’t consider heat relief for growing pigs to be an issue until mid-June since outside weather conditions aren’t ‘hot’ yet. However, the growing pig doesn’t care what outside conditions are when they are housed in confinement facilities. They react to the conditions provided by their care takers. If we don’t implement heat relief strategies until the calendar says it’s time or until we ourselves feel the need, the pigs will already have suffered a performance lag.

For curtain sided finishers, I generally recommend that wetting devices (misters/drippers) be set to turn on at 18 F above the room set point. If there are stirring fans used for additional heat relief, they should be set to begin operation at 15 F above set point. This means air movement is used to cool pigs first, and when air movement doesn’t result in pigs being kept within their thermal neutral zone, water is added as a source of evaporative heat loss. Every pound of water that is converted from a liquid to water vapor by evaporation results in 1050 btu of heat converted from sensible heat to latent heat.

In tunnel barns, the temperature settings for automatic wetting systems may need to be set slightly higher (20-22 F above set point) since these don’t turn on until all stages of ventilation are activated, meaning the air flow in the pig zone is often 350-450 fpm. This high rate of air flow results in very effective cooling of pigs when they have their skin wetted and are then allowed to dry.