How Heat Stress Impacts Swine Health

Pigs Cannot Handle the Heat

As temperatures increase, it not only impacts human health but also can be a major threat to swine agriculture. Researchers in 2003 estimated that heat stress results in an annual loss of about $300 million in the swine industry alone. With nine of the ten warmest years ever recorded occurring since 2005, that number has likely increased several folds.

Pigs are disproportionately affected by heat stress due to their physiology. They can only sweat at about two percent of the rate of the average human, so their ability to dissipate heat by evaporative cooling (through sweat) is virtually non-existent. Similar to canines, panting to dispel heat is one of pigs’ front line thermoregulatory responses. Another response is a shift in blood distribution so that there is more blood flow to the skin, where heat can be released at the body’s surface. While this is an effective way to release heat, it has its own set of problems. To shunt blood to the skin, blood vessels at the core constrict, resulting in reduced blood flow to essential organs. In the short term, this does protect those organs from overheating; however, if ambient temperatures remain high, the reduced oxygen can result in dysfunction. This leads to stress and reduced growth rate in pigs, profit loss to producers and price hikes for pork in the supermarket. At worst, sustained heat stress can be fatal to the animal.

Lauren Anderson examining pigs.

The upper critical limit is the temperature threshold at which the pig must utilize energy to dissipate heat from their body to maintain core temperature homeostasis. Danger ensues when temperatures sustain over the upper critical threshold for several days in a row. This occurs at a lower temperature than one might assume. Pigs’ ability to tolerate heat diminishes as they grow (See Figure 1). By the time they reach processing weight and about 280lbs, a pig’s danger zone is anything above 60 degrees Fahrenheit. North Carolina’s Duplin County is the number one hog producing county in the nation, boasting millions of hogs and a $614 million pig and pork product economy. It is also hot and getting hotter. The graph below clearly exemplifies that a significant portion of the year is above a pigs’ thermoneutral “safe-zone.”

Considering pork is one of the top protein sources in the world, heat is a concerning threat for both an animal welfare and food security. Pork producers must work hard to utilize misters, fans, and other mechanisms to protect their pigs. Their options grow slimmer as temperatures across the world continue to rise. I was fortunate to have part of my research at North Carolina State University revolve around early recognition and intervention in swine heat stress. Pigs were subjected to a very low intensity heat stress, at or below their upper critical limit temperatures and we found that behavioral changes and increased inflammatory biomarkers associated with heat stress occurred before the upper critical limit temperatures were exceeded. This may indicate that commercial pigs are even less heat tolerant than is currently accepted. This is not necessarily surprising. There have been immense genetic and nutritional advancements over the years that have improved pigs’ growth rates and pork production efficiency, but this has come at the cost of physiologic heat tolerance. Such advancements have helped maintain the balance between producer profitability and food affordability. However, our research suggests that it may be time to reevaluate the critical temperature limits and timing of interventions to protect this balance.

Figure 1: Temperature tolerance thresholds for pigs as they grow overlaid with the average summer (June to September) temperatures in Duplin County, North Carolina. Temperature source: NOAA.

Appreciation

I cannot possibly overstate how much I have learned in the FFAR Fellows program. I am so grateful to AgBiome, especially my mentor Dr. Vadim Beilinson, for making participation in this fellowship possible for me. I also want to thank my other industry mentor, Dr. Todd Armstrong, for his ongoing involvement in both my technical and professional development education. In addition, I am incredibly thankful for the opportunity to learn from other fellows. With a quick FFAR fellows group chat message, I can get opinions and advice from brilliant Ph.D. students all over the country from diverse agricultural fields. I am excited to see all that my fellow colleagues will accomplish because of this opportunity.