Producers speak
What swine farm managers believe about heat stress
By Jay S. Johnson and Kara R. Stewart
Heat stress continues to be one of the most costly and persistent challenges in pork production, particularly during summer months when barn temperatures rise. While science has long documented how heat stress can reduce pig growth performance, impair reproduction and increase mortality, little is known about how producers define and manage heat stress on their farms.
To close that gap, we surveyed 62 U.S. swine farm managers from across 16 states to learn how they perceive heat stress, what temperatures they believe trigger it in pigs, what technologies they rely on to manage it, and whether they see value in updated tools to support decision-making (Johnson and Stewart, 2025). Their answers offer some insight into where opportunities for improvement still exist.
Survey design and distribution To better understand how U.S. swine farm managers define and manage heat stress, we conducted a 10-question online survey, available in both English and Spanish (Table 1). Questions covered perceived heat stress thresholds by pig category, barn ventilation setpoints, cooling technologies used and the perceived impact of heat stress on pig health, welfare and productivity. Respondents were also asked whether a decision support tool would be beneficial for managing heat stress more effectively. The survey was distributed through university Extension networks, industry organizations such as the National Pork Board, and at the 2021 Midwest Boar Stud Managers Conference. Participation was voluntary and limited to individuals directly involved in managing swine operations.
The producers behind the dataSixty-two managers, representing operations across 16 states, completed the full survey. Most respondents managed large commercial herds, averaging 7,416 sows per farm, with herd sizes ranging from 180 to 35,000 pigs. Collectively, these managers oversaw a diverse array of pig categories: 87% had gestating sows, 85.5% had lactating sows and pre-weaned pigs, 83.9% had mature boars and 82.3% had non-pregnant sows. Fewer respondents reported managing nursery pigs (33.9%), grow-finish pigs (29.0%) or market pigs (19.4%).
Genetic diversity was also high among operations, with respondents reporting an average of 1.43 genetic lines per farm and 13 different genetic sources represented. Swine producers typically operated in more than one location, averaging 1.15 states per operation. Respondent profiles are are available in Table 2.
Producers know heat stress mattersNearly 90% of respondents agreed or strongly agreed that heat stress negatively affects pig productivity, and over 80% said the same for health and welfare as established in Figure 1. This consensus reinforces what decades of research have shown: heat stress compromises animal well-being and impairs performance.
Reduced feed intake, increased mortality and lower reproductive success are just some of the well-documented consequences of heat stress (Johnson, 2018), and producers appear to be acutely aware of these impacts. Notably, none of the respondents strongly disagreed with the statements regarding productivity, health or welfare, suggesting a broad recognition across the industry that heat stress is a serious and persistent challenge that requires attention and action.
Wide variation in perceived heat stress thresholdsProducer responses revealed substantial variability in the temperatures believed to trigger heat stress in pigs as shown in Figure 2. Reported thresholds ranged from as low as 15.6°C (60°F) to as high as 37.8°C (100°F), depending on the pig category. On average, the temperatures producers associated with heat stress were 1 to 3°C higher than those supported by current scientific evidence (FASS, 2020), with the greatest discrepancies observed in sows (McConn et al., 2021, 2022). For instance, while recent studies have shown that sows can begin experiencing physiological signs of heat stress at temperatures as low as 24°C (McConn et al., 2021, 2022), many respondents reported thresholds closer to 27°C or higher (Fig. 2).
This wide range highlights the potentially subjective and individualized nature of how heat stress is defined on-farm. Factors such as past experiences and even interpretation of animal behavior likely influence each manager’s perception. This lack of consensus may present a challenge for consistent implementation of heat mitigation strategies. If producers are unaware that pigs are already heat-stressed at lower temperatures than assumed, cooling systems may be activated too late or used inconsistently, increasing the risk of productivity losses and animal welfare concerns. These responses point to a clear need for updated, evidence-based guidelines and accessible decision support tools to help producers recognize and respond to heat stress more effectively across different stages of production.
Ventilation setpoints mirror threshold variabilitySimilar variation was evident in producers’ ventilation temperature setpoint practices as demonstrated in Figure 3. Reported high-temperature setpoints in gestation barns ranged from 18 to 35°C (64–95°F), while farrowing barns ranged from 20 to 35°C (68 to 95°F), a spread of 15°C in some cases (Fig. 2).
Many of these reported high ventilation temperature setpoints exceed temperatures where heat stress has already been demonstrated in modern sows, particularly during late gestation and lactation when metabolic heat production is elevated (McConn et al., 2021, 2022; Cecil et al., 2024).
This suggests a disconnect between producers’ perceptions of thermal comfort and the physiological needs of the pigs. While ventilation systems are designed to respond to rising temperatures by increasing airflow or activating cooling mechanisms, the effectiveness of these systems is limited if the temperature thresholds that trigger them are set too high. In practice, this could delay cooling interventions until after pigs have already begun experiencing heat stress, diminishing both the welfare and performance outcomes producers aim to protect.
The variability in ventilation strategies further emphasizes the need for clear, science-based recommendations that reflect the thermal sensitivities of today's swine genetics. Tailoring ventilation setpoints to align with validated heat stress thresholds, rather than relying on broad or outdated ranges, could help producers manage barn environments more effectively and prevent performance losses before they occur.
Cooling strategies rely heavily on traditional technologiesWhen it comes to cooling pigs, most producers continue to rely on familiar, well-established technologies. Fans and evaporative cooling pads were the most widely used systems, reported by over 65% of respondents as illustrated in Figure 4. These tools are relatively affordable, easy to implement, and often come standard in modern swine barns, which likely contributes to their widespread adoption.
However, other cooling options (i.e., drip coolers, sprinkler or mister systems, cooled flooring or dietary modifications) were used far less frequently. Some producers reported using customized or less common approaches like alcohol sprays or air conditioning, but these responses were rare. The limited adoption of alternative strategies may reflect concerns about cost, maintenance or complexity, but it may also indicate a lack of awareness or guidance on how to implement them effectively.
While traditional ventilation and cooling systems have served the industry well, they may not be sufficient to meet the needs of today’s high-producing pigs, especially as climate patterns shift and heat events become more frequent or intense. Modern pigs produce more metabolic heat than their predecessors (Brown-Brandl et al., 2014), increasing their vulnerability to heat stress even under conditions previously considered tolerable. These findings highlight the importance of exploring more advanced, adaptable, and pig-specific cooling technologies to ensure thermal comfort and maintain performance under increasingly challenging environmental conditions.
Producers see value in pig-specific decision support toolsOver 64% of respondents agreed or strongly agreed that a pig-specific heat stress decision support tool would benefit their operation as demonstrated in Figure 5. This interest suggests producers are not only aware of the challenges heat stress poses but may be open to adopting innovative tools to help manage it more effectively.
Current indices commonly used to assess heat stress risk (i.e., the Thermal Humidity Index or Livestock Weather Safety Index) were never developed with pigs in mind (Thom, 1959, LCI, 1971). Many rely on data from cattle (LCI, 1971) or even humans (Thom, 1959) and are based on environmental and physiological assumptions that no longer reflect the characteristics of modern swine production. Today’s pigs have been selectively bred for greater productivity, resulting in increased metabolic heat output and a reduced tolerance for elevated temperatures.
A real-time, pig-specific decision support tool could help bridge the gap between outdated thermal guidelines and the needs of contemporary production systems. Tools like the HotHog smartphone app available for iOS and Android, which incorporates validated heat stress thresholds for different sow production stages (McConn et al., 2022), represent a promising step forward. Expanding these platforms to include other production phases (i.e., nursery, grow-finish and market pigs) could offer producers even greater support in identifying risk and applying timely, targeted interventions. This kind of precision management has the potential to improve animal welfare, optimize resource use and safeguard productivity during periods of thermal stress.
Producers voice on-the-ground challengesSeveral respondents shared candid reflections on the day-to-day realities of managing heat stress, underscoring the complexity and persistence of the issue (Table 3). Common concerns included wide temperature fluctuations that fail to activate cooling systems in time, leaving pigs vulnerable during short but intense heat spikes. Many highlighted the ongoing challenge of balancing the differing thermal needs of sows and piglets, particularly in farrowing barns, where maintaining environments that support both lactation and neonatal piglet survival can be difficult.
The physical demands placed on caretakers working in hot, poorly ventilated barns also emerged as a key theme. Producers noted that heat stress doesn’t just affect animals, it strains the workforce as well, increasing fatigue and reducing overall efficiency. Others expressed concern over the impact of heat stress on reproductive performance, particularly in boar studs, where high temperatures and humidity can compromise semen quality, storage and transport.
Finally, several respondents emphasized the need for smarter environmental monitoring tools, alert systems that go beyond simple temperature readings to consider humidity, air movement and stage-specific risk thresholds. These comments reinforce the need for more responsive and nuanced tools that can support both animal care and caretaker well-being during increasingly frequent and unpredictable heat events.
What does it all mean?The take-home message from this survey is clear: producers recognize heat stress is a serious issue, but they don’t all agree on when it starts, how best to manage it or what tools are available to help. By updating our industry’s understanding of heat stress thresholds and providing modern, pig-specific tools for decision-making, we can help producers make smarter, more consistent management choices, ultimately improving pig welfare and production outcomes.
Acknowledgements:We thank the producers who participated and shared their valuable time and perspectives. Furthermore, we thank the Extension educators, the National Pork Board and the organizers and attendees of the 2021 Midwest Board Stud Managers Conference.
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Cecil, M.R., S.M. Neeno, M.K. Byrd, T. Field, J.N. Marchant, J.Q. Ni, B.T. Richert, A.P. Schinckel, R.M. Stwalley, and J.S. Johnson. 2024. Evaluating the impact of macroenvironment temperature on thermoregulatory and milk quality parameters in lactating sows and their litters. J. Anim. Sci. 102 (Suppl. 2): 31-32. Doi: 10.1093/jas/skae102.038.
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LCI. 1970. Patterns of transit losses. Omaha, NE: Livestock Conservation, Inc.
McConn, B.R., B.N. Gaskill, A.P. Schinckel, A.R. Green-Miller, D.C. Lay Jr., and J.S. Johnson. 2021. Thermoregulatory and physiological responses of non-pregnant, mid-gestation, and late-gestation sows exposed to incrementally increasing dry bulb temperature. J. Anim. Sci. 99: 1-8. Doi: 10.1093/jas/skab181.
McConn, B.R., A.P. Schinckel, L.R. Robbins, B.N. Gaskill, A.R. Green-Miller, D.C. Lay Jr., and J.S. Johnson. A behavior and physiology-based decision support tool to predict thermal comfort and stress in non-pregnant, mid-gestation, and late gestation. J. Anim. Sci. Biotechnol. 13:135. Doi: 10.1186/s40104-022-00789-x.
Thom, E. C. 1959. The discomfort index, Weatherwise 12(2): 57–60.
Johnson is an associate professor in the Division of Animal Sciences at the University of Missouri and Stewart is director of boar production for Smithfield Foods.
