Cool for the summer: 3 tips to reduce heat stress in pigs
Happy swine are essential to having a productive and profitable herd, yet pigs are very sensitive to changes in the environment, especially temperature. It is important to keep pigs within their thermoneutral zone in order to maintain fertility throughout the year and maintain high feed intake and growth rate throughout the summer months.
Why are pigs so sensitive to heat stress?
Pigs are more prone to develop symptoms of heat stress than other mammals. This is because:
- They lack the ability to sweat and have relatively small lungs for their body size, making it difficult for them to remove excess internal heat.
- They also have a thick layer of subcutaneous fat, which provides useful insulation in cold weather but makes thermal regulation in hot weather more difficult.
- The genetic improvements in pig breeds that are geared toward higher growth performance and lean gain mean that pigs raised in the early 2000s produced around 20 percent more internal heat, generated from respiration and metabolism, compared to pigs in the early 1980s, and this is thought to have increased by around an additional 10 percent in the last decade.
Consequences of heat stress on the performance of pigs
Pigs under heat stress will reduce their feed intake, drink excessive amounts of water (increasing loss of electrolytes and potential mineral imbalances) and accumulate acids produced within the body (causing a loss of acid/base balance). Such changes in the body can eventually result in diarrhea or death, in severe cases.
Experimental trials have mimicked heat stress conditions in pigs in order to examine the physiological changes that occur in detail. Exposure to 35 degrees Celsius for 24 hours significantly damaged the intestinal defense function and increased plasma endotoxin levels. Even when pigs are exposed to short periods of heat stress, which may only last two to six hours, the immune system in the gut is significantly compromised, leading to more potential for pathogenic organisms to colonize the intestines and cause disease. This is more common in pigs housed in conditions of poor hygiene or higher exposure to pathogens.
Pigs subjected to high temperatures will have reduced growth rates (by up to 50 grams per day), and, in the breeding herd, farrowing rates could decline by as much as 25 percent, with litter size showing a small drop as well. As pigs grow, their susceptibility to heat stress increases in line with body size (and relative lung size) and subcutaneous fat.
The effect of body size has been studied in relation to heat stress, which is demonstrated in Figure 1 and 2.
Figure 1. Effect of ambient temperature on the average daily gain of grower-finisher pigs
Figure 2. Pig bodyweight has a significant effect on the critical temperature for average daily feed intake (ADFI) and average daily gain (ADG)
When do pigs encounter heat stress?
Heat stress is initiated when ambient temperature and humidity increase. For example, pigs can develop heat stress at much lower temperatures when the humidity is high, so this, as well as temperature, needs to be carefully regulated in housing. Recently, Iowa State University created a heat stress index chart for pigs (Figure 3) to assist with management strategies to reduce heat stress in pigs by identifying when such problems are likely to manifest.
Figure 3. This heat stress chart combines the effects of both temperature and relative humidity to provide classifications as “alert,” “danger” and “emergency” zones for grower-finisher pigs
Reduce heat stress in three steps
1. Manage the environment
2. Ensure proper feed intake
3. Manage feed heat increment
The heat increment of feed is higher in low digestible raw materials with high fiber or high crude protein diets. Using Synergen® from Alltech can improve digestibility, therefore reducing the heat generated during digestion.