Heat Stress: An Overview

As a first REAL article, it made sense to address the Floridian’s curse during the summer shows: HEAT! While other states may complain during the months of June to August, we have the blessing of enjoying 100-degree days from March until mid-October, in some years. But, besides our summer complaints, how does heat stress work in pigs? [1]

Mechanism and Effects

The main mechanism of how is quite simple, unsurprisingly. Heat flows from the air, ground, or other contact surface into the pig’s body, causing their internal temperature to rise. Due to pigs’ limited sweat glands, pigs cannot effectively reduce their temperature through external evaporative cooling, so their main method to rid themselves of excess heat is panting. Panting essentially turns the upper airways into a heat exchanger that moves air quickly over the mucosal membranes, allowing saliva and other liquids to evaporate and carry excess heat with them. However, while this may help them not cook their internal organs, panting and excess heat still present serious problems. There are two main downstream effects of excess heat that drive the majority of the worst effects. [2, 3]

1. Panting > Hyperventilation > Acid-Base Imbalance

   This is among the main drivers of heat-induced physiologic stress, and we will discuss this extensively later in the article. As panting increases in rate, the animals’ acid-base balance and dEB (dietary electrolyte balance), which are delicately maintained by the kidneys, GI tract and the respiratory system, are thrown off track. Combining this with the second main effect of heat leads to acidosis, which wreaks havoc on numerous bodily systems. [4-6]

2. Peripheral Vasodilation

   As internal heat rises, the body is forced to dilate blood vessels in the extremities (scalp, cheeks, feet) in order to shed more heat. This leads to a cascade of problems as blood is redirected away from the gastrointestinal tract, leading to depressed immune response, decreased appetite, decreased nutrient absorption, and even a substantially suppressed metabolism. [7-9]

We are left with a list of nasty symptoms that are very bad for our goals in the ring, so the question becomes: What can we do about it?

An Ounce of Prevention = A Pound of Cure

This old saying holds true for heat stress! We need to focus as much as we can on prevention before we HAVE to treat it. We will discuss both prevention and cure via two mechanisms: these are practical tips and supplementation.

Practical Tips

1. VENTILATION

   Studies consistently show that moving air is essential in preventing heat stress. Every pig needs an effective fan, a well-ventilated pen, and SHADE! [3,10]

2. APPLY WATER EFFECTIVELY

   A simple drip cooler can be an amazingly effective preventive for heat stress by helping hogs mimic the evaporative cooling from sweat. Even just a few drops of water falling into their pen every 15-20 seconds allows them to cool significantly more than air alone.[11,12]

3. AVOID STRESSORS

   This one is difficult if you have to travel or show on a hot day, but simply avoiding an increase in physical activity during the hottest part of the day can do wonders to reduce the stress on an animal’s body. [12]

4. MEAL TIMING

   Digestion is thermogenic, meaning it produces heat in the body. This is why they naturally shift their appetite to be hungrier in the cooler part of the day, which is when you should feed them. This ensures that they are absorbing nutrients and processing food without the added stressor of heat. [13]

Supplementation

1. FRESH, COOL, CLEAN WATER

   This one is obvious, but essential. Drinking cool, clean water and ensuring constant access is the first step in prevention. [12]

2. dEB (Dietary Electrolyte Balance) + Acid-Base

   This was one of the effects of panting we touched on earlier. This factor directly affects almost every organ system, so it is essential to address it. However, most go about it in a completely incorrect manner. Pigs do not lose salts through their sweat in nearly the volume we do. Most of their water loss comes from panting, which, together with peripheral vasodilatation, drives net acidosis in the body. So supplementing salts like NaCl and KCl that are high in CL+ ions isn’t as helpful for pigs as it would be for us. This means throw out your Gatorade powders, Liquid I.V., and any other salt-based electrolyte, because it is simply far below optimal for pigs. Instead, we want to focus on compounds that both balance electrolytes and help the body raise the pH back to normal levels. This is primarily NaHCO3, commonly known as baking soda, and KHCO3, potassium bicarbonate. You can also use other carbonate compounds, but supplementing potassium bicarbonate for show pigs seems to work well because most diets are already high in both Na and Cl ions. [2,4–6,14,15]

3. Betaine

   Betaine is an amino acid shown repeatedly in studies to reduce respiratory rate, rectal temperature, and even improve gut permeability under heat stress. Behind electrolyte balance, I’d argue it is the other must-have for heat stress prevention and treatment. [16,17]

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Concluding Thoughts

This article is a very basic overview of a deep and interesting issue of swine physiology that I am sure I will cover again in greater detail; however, I think the most important takeaway is that heat stress, like most issues in animals, comes down to how well you monitor and take care of your animals. Even in Florida, with proper cooling techniques and supplementation, it’s possible to mitigate heat stress. It requires you to pay attention to their condition and critically evaluate what you can improve, and I hope this article was helpful in doing that. Stay tuned, as I have some fun articles planned on muscle gain in pigs, stress gene, and I may even have a special guest writer sometime soon! Until next time…

God bless,

Dean Daniels

References

Florida Climate Center. Florida’s Hot Season. Accessed 2025. Florida Climate Center

1. Gourdine JL, et al. The Genetics of Thermoregulation in Pigs: A Review. Front Vet Sci. 2021. PMC

2. Godyń D, Herbut P, Angrecka S, Corrêa Vieira FM. Use of Different Cooling Methods in Pig Facilities to Alleviate the Effects of Heat Stress—A Review. Animals (Basel). 2020;10:1459. MDPIPubMed

3. Cottrell JJ, et al. The Effect of Heat Stress on Respiratory Alkalosis and Insulin Sensitivity in Pigs. Animals (Basel). 2020;10:690. MDPIPubMed

4. Haydon KD, West JW, McCarter MN. Effect of dietary electrolyte balance on performance and blood parameters of growing-finishing swine fed in high ambient temperatures. J Anim Sci. 1990;68:2400–2406. PubMed

5. Kansas State University Swine Nutrition Guide. Dietary Electrolyte Balance (general and nursery). Accessed 2025. Animal Sciences and Industry+1

6. Abuajamieh M, et al. The effect of recovery from heat stress on circulating bioenergetics and metabolic function in pigs. PLOS One. 2018. (Peripheral vasodilation reduces splanchnic blood flow.) PMC

7. Pearce SC, et al. Heat stress reduces intestinal barrier integrity and favors intestinal glucose transport in growing pigs. PLOS One. 2013;8:e70215. PLOSPubMed

8. Ringseis R, et al. Heat stress in pigs and broilers: role of gut dysbiosis in the impairment of intestinal barrier function and immune system. J Anim Sci Biotechnol. 2022;13:111. BioMed Central

9. Wageningen University & Research. Review on cooling technologies for pigs. 2024. Wageningen University & Research eDepot

10. National Hog Farmer. Direct cooling with stir fans and sprinklers. Guidance on timer cycles and droplet size. National Hog Farmer

11. Penn State Extension. Keeping Pigs Cool in the Summer Heat. 2023/2025. (Wet–dry principle; shade; ventilation; water access.) Penn State Extension+1

12. de Oliveira MJK, et al. Feeding Behavior of Finishing Pigs under Diurnal Cyclic Heat Stress. Animals (Basel). 2023;13:908. MDPIPubMed

13. Sodium bicarbonate (NaHCO₃). Wikipedia. Accessed 2025. (Commonly known as baking soda.) Wikipedia

14. Potassium Bicarbonate (KHCO₃). PubChem CID 516893. Accessed 2025. PubChem

15. Mendoza SM, et al. Effects of dietary supplementation of the osmolyte betaine on growing pig performance… under thermoneutral and heat-stressed conditions. J Anim Sci. 2017. (0.10% betaine ↓ rectal temp; ↓ RR under HS.) PMCPubMed

16. Le HH, et al. Betaine and Isoquinoline Alkaloids Protect against Heat Stress and Colonic Permeability in Growing Pigs. Antioxidants. 2020;9:1024. MD