As temperature and humidity levels rise in the summer months, so does the threat of heat stress in the swine herd.
Heat stress can occur in finishing pigs, boars and sows at temperatures of 70° F (21° C) with performance decreases after just 2 to 4 consecutive days of temperatures above 80° F (27° C).
Making a few minor ration modifications can help minimize reductions in average daily gain; reduce the heat produced during digestion, absorption and assimilation of dietary nutrients; and encourage the deposition of lean muscle over fat during the heat of summer1.
Today’s lean, highly muscled pigs produce substantial amounts of heat simply through food consumption. “The heat-increment of feeding causes a pig’s body temperature to increase due to feed digestion,” explains Lance Baumgard, PhD, Jacobson Professor of Nutritional Physiology in the Department of Animal Science at Iowa State University.
The combination of increased environmental temperatures and the heat-increment of feeding quickly compounds the effects of heat stress.
Pigs experiencing heat stress immediately reduce feed consumption and increase water intake, which sets off a cascade of metabolic events within the animal. Not only does heat stress reduce average daily gain, it also produces carcasses with higher fat content.
Encouraging feed consumption
Increasing fat levels while reducing crude protein and fiber in the ration help decrease heat production during digestion while encouraging feed intake. Increasing the nutrient density of rations also helps ensure that vitamin, mineral and trace-mineral needs are met during periods of reduced feed consumption.
“Adding supplemental fat to the ration not only increases dietary density but also reduces the amount of heat generated during digestion,” Baumgard says, “The heat increment of fat is lower than proteins and carbohydrates.”
The negative effects of decreased feed intake due to heat stress can be mitigated by reducing crude protein content by 2% through the use of synthetic amino acids. “Excess dietary crude protein costs energy to get rid of surplus nitrogen and creates additional heat during this process,” he explains.
Another ration adjustment that affects heat production is reducing the level of fiber. “Fiber is responsible for the largest heat-increment production in the ration,” Baumgard adds.
Changing the physical characteristics of feed through the addition of water or the use of liquid feeding systems encourages consumption during hot weather.
Under heat-stressed conditions, daily water use can increase as much as six times the normal amount — up to 30 gallons per day per finishing pig. Good-quality water must be available to all animals 24/7 with no more than 12 to 15 pigs per nipple or cup in the finishing barn.