Maintaining Growth During Summer
By Dr. Mike Brumm, Brumm Swine Consultancy, Inc.
In previous years, nutritionists often increased the amount of fat added to a growing pig’s diet to counteract the reduction in caloric intake in hot weather. However, the prices for choice white grease and other dietary fat sources has increased to the point that many nutritionists have determined that it is not a cost effective feed ingredient, even when compared to corn at $5.50+ per bushel. So this summer attention to cooling management strategies will be increasingly important.
One of the first responses a growing pig makes when it is forced to live in an environment that is above its upper critical temperature is a reduction in feed intake. This classic response to warm conditions results in a decrease in daily gain. If conditions remain warm for a period of time, feed conversion may also worsen as the pig uses a higher percentage of its limited daily feed intake for maintenance needs versus growth.
Many misconceptions remain in the pig industry regarding when or even if to cool grow-finish pigs. These misconceptions have increased as many producers have moved to tunnel ventilated finishers. The assumption many producers and advisors make is that with the artificial ‘wind chill’ of a tunnel barn, the addition of supplemental water via sprinklers for evaporation is not necessary.
In tunnel finishing facilities, the design goal when in full tunnel mode is an air velocity in the pig zone of approximately 300-350 feet per minute. This value is used as this velocity maximizes heat exchange by the growing pig with its surroundings. If air moves faster than this over a pig, there is only limited additional heat exchange with the moving air at summer air temperatures.
The skin temperature of a pig is normally around 95 degrees F. When we move 80-degree F air over the pig’s 95 F skin surface, cooling occurs due to the difference in temperature, a process know as convection. As the air temperature increases, less heat can be transferred from the pig to the moving air because there is less temperature difference. If we blow 100 F air over the 95 F skin surface, heat flows from the moving air to the cooler pig skin surface, meaning the pig becomes warmer, and the faster we move hot air over the pig, the faster it may warm up. On hot days, air movement alone is insufficient for the growing pig to remain in its thermal neutral zone.
To help the pig remain within its thermal neutral comfort zone in warm to hot conditions, evaporative cooling must be provided. The most effective form of evaporative relief for the pig is direct wetting of the skin, followed by a period of evaporative drying. There is approximately 1050 BTU of heat relief for every 1 lb of water evaporated from the pig’s skin.
The available data suggests that producers begin wetting growing-finishing pigs anytime the air temperature is 80 F or warmer. The general recommendation is that the sprinklers wet no more than 60% of the pen area in 2 minutes or less of “on” time. The sprinklers should then remain “off” for 15-30 minutes to allow for the cooling to occur during the evaporation of the water from the pig’s skin. Maximum cooling occurs during this evaporation period, not during the wetting period. The correct “off” period can be determined by observation of the pigs and flooring. When the cement slats begins drying between cycles, decrease the “off” time as the pigs are transferring heat to the cement slats to dry the slats, rather than evaporating water directly from their skin surface.
For tunnel ventilated facilities, sprinklers should be equipped with flat fan nozzles oriented parallel to the air stream. This minimizes water evaporation into the air stream and maximizes wetting of the pigs. For curtain sided facilities, hollow cone nozzles are recommended. In both types of facilities, large droplet sizes are recommended as the goal is to wet the pig, not to evaporate water into the surrounding air.
In research with 113-pound pigs at the University of Kentucky, blowing air over pigs at 500 feet per minute beginning when air temperatures were 78 F improved daily gain 7.3 %. Sprinkling pigs beginning at 78 F improved daily gain 11.3% and the combination of the two improved gain 13.2% versus doing nothing to assist the growing pig with heat relief.
Dr. Mike Brumm is the owner of Brumm Swine Consultancy, Inc. of North Mankato, Minnesota. He was previously a professor at the University of Nebraska. Dr. Brumm's areas of expertise include management and housing of the growing pig, industry issues including production networks, contracts, cost of production and record systems.
|
