While it has been ‘warm’ in the Midwest this past week, it is nothing like conditions on the east coast. As I write this weeks blog, it is currently 89F in Clinton, NC with a dew point of 71F and predicted high temperature of 93F. Clinton is in the middle of the North Carolina pork production region. Thus, the definition of warm or hot depends on location.
For the pig, location doesn’t affect how it responds to heat. For grow-finish pigs, supplement wetting to assist in cooling is necessary when ever air temperatures get into the low 80’s. For curtain sided barns, I generally recommend that stir fans (if the barn has them), be set to turn on at 15F above the room set point in the controller. Set the sprinklers to turn on at 18F above set point.
For tunnel barns, I generally set the sprinklers to turn on at 20F above set point. In tunnel barns, by 20F, all of the tunnel fans are operating, and air flow in the pig zone is most likely 350+ fpm. When the pigs are wet by the sprinkler, they dry (loose heat) relatively rapidly. To avoid chilling of pigs, I am ok with wetting them beginning a few degrees warmer than I would wet them in a curtain sided barn.
For both tunnel and curtain barns, the sprinkler system should be capable of wetting 60% of the pen area in less than 2 minutes. Do not use fine mist nozzles to wet pigs. Fine mists cool the air above the pigs. The most effective cooling occurs when the pig evaporates the water from its skin, rather than by loosing heat to cooler (but more humid) air. Fine mists drift and don’t land where intended in the pen. In curtain barns, on windy days it’s not uncommon to have the grass on the north side of the barn very wet, with pigs in the south row of pens barely wet. In tunnel barns, the mist gets carried to the tunnel fans.
In reviewing literature on the impact of heat on grow-finish pigs this past week, many articles talk about using 0.1 gal/pig/hr as the target for cooling water use. I don’t know if this is right or not. In a 1200 head room, this is 120 gal/hr. If the cooling line runs 2 minutes out of 15, this is a total of 8 minutes of on-time per hour. This means the flow to the cooling line needs to be 15 gal/min. If the cooling line is supplied by a ¾” PVC pipe, the maximum flow rate is only 5.5 gal/min. I see many barns with comfortable pigs when a ¾” line is used so I suspect the 0.1 gal/pig/hr number isn’t correct.
What is correct is that the pigs should be thoroughly wet in less than 2 minutes of ON-time and then allowed to dry. Generally I recommend starting with 15 minutes of OFF time and adjusting as necessary. When the floor under the pigs begins to dry, this is a signal that it is time to re-wet the pigs.