Unless you live in a foreign country, you know it has been hot this week in the regions of the US where pigs are grown. Dew point temperatures in the upper Midwest have been in the upper 70’s to low 80’s during the day and have only declined to the upper 60’s in early morning hours, with air temperatures remaining above 75 in the overnight hours.

This sustained heat has taken its toll on pigs. Normally federally inspected barrow and gilt carcass weights are 1.3 lb heavier on Thursday compared to Monday and Tuesday weights. Yesterday’s (July 21) weights were only 0.1 lb heavier, dramatic evidence that feed intake has dropped in barns this week, with the immediate result being a decline in slaughter weights.

I received a call from a client this week asking about running sprinklers 24-7 in hot weather for market weight pigs. My immediate answer is yes! If pigs are hot we need to provide all the help we can in helping them dissipate this heat.

There is always a lot of discussion on how to best cool growing pigs, both in regard to sizing of sprinkler packages and controller settings to run these sprinklers. The following is what I teach in our 4-state ventilation workshops.

• Wet the pigs using big droplet sizes, not fine mists. Fine mists cool the air above the pig and don’t do a good job of thoroughly wetting the pig’s skin. The pig loses the most heat evaporating water from its skin so a thorough wetting is desired. In addition, big droplets don’t drift in the wind (ventilation system air currents) as much so less water ends up going out exhaust fans or north sidewall curtain openings.
• Nozzles should be sized and plumbed so approximately 50-60% of the pen gets wet and pigs get thoroughly wet in 2 minutes of ON time. Increasing the ON time will not improve the effectiveness of wetting if the 2 minute period results in all pigs having a chance to get wet. The pig does not cool very well during the ON time as blood vessels will vaso-constrict when water is applied to the skin.
• Start with a 20 minute OFF (drying time). If the flooring under the pig begins to dry before the 20 minutes are up, reduce this OFF time.
• I generally start with the wetting beginning at 18-20F above controller set point. This assumes a 60-62 set point for pigs above 180 lb. I want to be wetting 180 lb or bigger pigs by 80-82F. Waiting to wet big pigs until 85-90F because you are afraid of sick pigs is really an indication that you’ve mis-managed the wetting strategy in the past and are giving up performance because of prior mis-management.
• If you feel you must turn off the misters to all floors to dry to prevent feet and leg problems, don’t do it until at least 2 am. Your facilities are at their highest temperatures at 6-7 pm so you need to give the ventilation system time to remove this heat. I told the client mentioned earlier that if they wanted 4 hour of drying time, you could turn off the sprinkler system from 5 to 9 am as this is the coolest time of the day.