2024

Beating The Heat

Keeping pigs cool and comfortable on the farm

by Dr. Jay S. Johnson, PhD, Dr. Luiz F. Brito, PhD, and Dr. Allan P. Schinckel, PhD

Within the pork industry, heat stress poses a significant threat to overall pig production, impairing health, productivity, and well-being at all life stages.

Understanding the mechanisms and implications of heat stress is crucial for producers to mitigate its effects and ensure proper animal well-being and industry sustainability.

Postnatal heat stress occurs when pigs are exposed to high temperatures, leading to physiological and behavioral changes that can impact their growth and overall health (Figure 1).

image showing effects on heat stress on pigs
Figure 1. Effects of heat stress on physiological responses of pigs. Adapted from Johnson et al. (2015a).

Heat stress can cause a reduction in feed intake, meaning slower growth and decreased productivity. There may also be a behavior change—more time lying down and less activity—to dissipate heat and reduce metabolic heat production.

Heat stress during pregnancy can have an even more profound effect on pig production. Sows exposed to high temperatures during gestation may experience reduced reproductive performance, including lower conception rates and increased embryonic mortality.

Furthermore, heat stress during pregnancy can affect the prenatal development of their piglets, leading to lower birth weights, higher mortality rates after birth, and long-term negative effects on piglets throughout their postnatal life (Figure 2; Johnson and Baumgard, 2019; Johnson et al., 2020).

chart showing swine lifecycle
Figure 2. Postnatal phenotypic changes in pigs exposed to in utero heat stress. Adapted from Johnson and Baumgard (2019).

Heat stress research has highlighted the importance of managing thermal comfort in pig facilities.

By providing adequate ventilation and cooling systems and understanding the thermal requirements of the modern pig, producers can help mitigate the negative effects of heat stress on their animals. Nutritional strategies of adjusting feed formulations and supplementing diets with electrolytes, trace minerals, and antioxidants can support pigs’ health and performance during periods of heat stress.

Furthermore, genetic and genomic selection for improved heat stress tolerance may be an effective strategy to improve resilience and reduce the negative effects of heat stress on pigs and their developing offspring.

Technology and Heat Stress Mitigation

Mitigating heat stress in pigs requires a multifaceted approach to address management practices and environmental conditions.

Producers can employ various strategies to create a comfortable environment for their pigs during times of heat stress and minimize the negative effects on pig performance and well-being. The first step in mitigating heat stress is understanding what environmental conditions can cause pigs to become heat-stressed.

Decision-support tools in the form of smartphone applications such as HotHog (Figure 4) are available to producers and allow for real-time predictions of thermal comfort and stress levels. These predictions are based on location and production stage, allowing pig producers to make informed decisions about how to best protect their pigs from heat stress. By leveraging technology and data-driven insights, pig producers can implement proactive measures to minimize the negative effects of heat stress on their operations.

snapshot of HotHogs App
Figure 4. The HotHog home screen (left); management and mitigation screen (right). Available for free in the Apple App Store or Google Play.

Once heat stress risk levels can be identified, one of the most effective ways to mitigate heat stress on swine farms is through the use of conductive heat loss cooling systems.

sow laying on cooling pad
Figure 5. A lactating sow using an electronically controlled sow cooling pad.

Cooling pads, such as those developed by Purdue University (Figure 5), can aid in dissipating heat (Figure 6A).

This can result in downstream positive impacts on piglet growth under heat-stress conditions (Figure 6B).

graph showing cooling pad effect on body temperature and weaning weight
Figure 6. The effects of an electronically controlled sow cooling pad on (A) lactating sow body temperature, and (B) litter weaning weights Adapted from Johnson et al. (2021).

Proper ventilation is another essential component of heat stress mitigation in pig farms. Ventilation systems help remove excess heat, moisture, and airborne contaminants from pig facilities, creating a healthier and more comfortable environment for the animals. By optimizing airflow and temperature distribution, producers can ensure that pigs have access to fresh air and reduce the risk of heat stress.

Overall, mitigating heat stress in pig farms requires a comprehensive approach that addresses environmental conditions, management practices, and incorporates technological solutions.

By implementing cooling systems, optimizing ventilation, and leveraging technology to monitor and manage heat stress, producers can create a more comfortable environment for their pigs, thereby improving productivity and well-being during times of heat stress.

Nutrition and Heat Stress Management

Nutrition is key to managing heat stress in pig production.

During periods of high temperatures, pigs may experience changes in feed intake and nutrient requirements, which can impact their growth and overall health. Therefore, farmers must adjust their feeding strategies to ensure that pigs receive adequate nutrition to support their well-being during heat stress.

One key consideration in nutrition and heat stress management is maintaining the overall hydration levels of the pigs. Heat-stressed pigs may drink more water to regulate body temperature and replace fluids lost through panting.

Producers should ensure that pigs have access to clean and fresh water at all times to prevent dehydration and support their physiological needs during periods of heat stress. Furthermore, water-delivered supplements have been shown to be effective in helping pigs recover from heat stress events.

Optimizing feed formulas can help support pigs’ health and performance during heat stress. Feeds supplemented with electrolytes, trace minerals, and antioxidants can replenish lost nutrients and support pigs’ physiological functions under heat-stress conditions.

In addition, attention should be paid to the energetic requirements of pigs exposed to heat-stress conditions.

chart comparing feed intake and avergae daily gain
Figure 7. (A) Feed intake and (B) average daily gain (ADG) of gestating gilts limit fed 1.82 kg per day and exposed to heat stress (HS) or thermoneutral (TN) conditions. Adapted from Byrd et al. (2022).

For example, although ad libitum-fed growing-finishing pigs often grow slower under heat-stress conditions, heat-stressed gestating gilts that are limit-fed following routine production practices grow faster when compared to those housed under thermoneutral conditions (Figure 7). This is likely due to the reductive effects of heat stress on the maintenance costs of pigs (Figure 8), which may result in a more positive energy balance for heat-stressed versus thermoneutral-exposed pregnant gilts that are limit-fed (Figure 9). Pig producers can work with nutritionists to adjust feed formulations and ensure that pigs receive balanced diets that meet their nutritional needs during periods of high temperatures.

chart showing maintenance costs and heat stress
Figure 8. Maintenance costs of growing and finishing pigs exposed to heat stress (HS) or thermoneutral (TN) conditions. From Johnson et al. (2015b, c).

chart showing energy utilization versus maintenance costs
Figure 9. Energy utilization for growth vs maintenance costs in limit-fed gestating pigs exposed to heat stress (HS) or thermoneutral (TN) conditions.

Lactating sows are particularly susceptible to heat stress, as selection for increased sow productivity has increased their heat production by over 50 percent in the past 40 years.

As a result, high environmental temperatures negatively impact their milk production and, consequently, affect the growth and development of nursing piglets.

Heat-stressed sows can also have delayed estrus after weaning and reduced conception rates.

Producers should pay close attention to the nutritional needs of lactating sows during heat stress and provide supplemental feeds to support milk production and piglet growth. However, it is important to note that nutritional support may not always result in improved piglet growth under heat stress conditions, as heat stress has a direct and negative impact on milk production independent of improved feed intake (Black et al., 1993; Johnson et al., 2021).

Therefore, nutritional strategies should be coupled with appropriate cooling technologies for maximum benefit.

Harnessing Genetics & Genomics to Combat Heat Stress

Genetic selection offers promising opportunities for developing pig populations that are more heat-stress resilient.

By developing genomic prediction models and identifying genetic markers associated with heat tolerance and thermoregulatory efficiency, researchers can breed pigs with enhanced resilience to high temperatures and reduce the negative effects of heat stress on animal well-being and productivity.

Through selective breeding programs, producers can prioritize traits related to heat tolerance and incorporate them into their breeding objectives. This may include selecting breeding stock with superior heat stress resilience based on thousands of genomic markers, which is already a common practice in pig breeding programs.

By selecting heat-tolerant pigs, producers can develop populations of pigs that are better adapted to hot climates and less susceptible to the negative effects of heat stress while still maintaining high productivity levels.

Breeding program effectiveness requires the identification of traits that are heritable, repeatable, and can be measured in a large number of individuals in a cost-effective and non-invasive manner.

Recent research has identified multiple indicator traits that can be used in breeding programs, including automatically-recorded vaginal temperature, skin temperature, and respiration rate (Johnson et al., 2023; Freitas et al., 2023).

In addition to the definition of novel traits for breeding purposes and the development of genomic prediction models, research into the genetics of heat stress tolerance in pigs has identified several candidate genes and genetic markers associated with heat tolerance and thermoregulatory efficiency.

By leveraging this genetic and genomic information, researchers and producers can accelerate the breeding process and develop more heat-tolerant pig populations that exhibit improved resilience to high temperatures and heat-stress conditions.

Research by our group has shown that various indicators of heat stress response are moderately heritable and that genomic prediction of heat stress tolerance can clearly distinguish more heat-tolerant animals from more heat-sensitive animals (Figure 10; Freitas et al., 2023).

chart showing breeding values for heat tolerance
Figure 10. Estimated breeding values for heat tolerance and heat stress sensitivity in lactating sows. Adapted from Freitas et al. (2023).

By utilizing genomic selection techniques, researchers and breeders can help enhance the efficiency and precision of breeding programs and develop more heat-tolerant pig populations more rapidly and effectively, as genetic progress is permanent and cumulative over generations.

In conclusion, genetic and genomic selection offer promising opportunities for developing pigs that are more heat-stress resilient. By identifying genetic markers associated with heat tolerance and developing genomic prediction models to calculate the genetic merit of breeding animals (candidates for selection), researchers and producers can develop more heat-tolerant pig populations that are better adapted to hot climates and less susceptible to the negative effects of heat stress while maintaining sustainable production and reproduction levels.

By utilizing continued research and innovation, genetic selection can play a critical role in the improvement of the resilience and sustainability of pig production systems in the face of climate change and environmental challenges.

Conclusions and Future Directions

Addressing heat stress in pig production necessitates a multifaceted approach that needs to encompass management practices and technological innovations, nutritional considerations, and genetic and genomic selection.

The research underscores the significance of understanding the physiological and behavioral impacts of heat stress across different life stages, from postnatal growth to prenatal development.

Mitigation strategies such as adequate ventilation, cooling systems, and optimized nutrition are pivotal for maintaining pig health and productivity during periods of elevated temperatures. Moreover, harnessing genetic and genomic advancements presents promising avenues for developing more heat-tolerant pig populations, offering long-term resilience against climatic variations.

Continued advancements in these areas hold the key to fostering sustainable pig production systems resilient to the challenges posed by heat stress and climate change.

As we move forward, collaborative efforts between researchers, producers, and technological innovators will be crucial in ensuring the well-being and productivity of pigs in a changing environment.


Dr. Luiz F. Brito, PhD

Dr. Luiz Brito is an Associate Professor of Quantitative Genetics and Genomics in the Department of Animal Sciences at Purdue University. Luiz also holds Adjunct Faculty positions at the University of Guelph in Canada and at the University of Nebraska-Lincoln.

Dr. Jay S. Johnson, PhD

Dr. Jay S. Johnson is the Supervisory Research Animal Scientist (Research Leader) of the USDA-ARS Livestock Behavior Research Unit in West Lafayette, IN USA specializing in stress and nutritional physiology.

Dr. Allan P. Schinckel, PhD

Dr. Allan P. Schinckel is professor of animal science in swine genetics and modeling with BS from Iowa State and MS and PhD from the University of Nebraska. He teaches course in pork production, design of breeding programs and modeling of pig growth and nutrient requirements. Dr. Schinckel has recently been involved in heat stress research and the use of electronic cooling pads for boars and sows.