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Minimizing the impact of heat stress

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Optimizing air speed is a vital part of keeping pig comfortable.

With warmer months approaching, mitigating the effects of heat stress becomes critically important for pork producers. Heat stress can easily be identified by farm employees who may observe pigs with decreased activity and full recumbency, increasing spacing from other pigs in the pen, increased respiration rates and panting, and in severe instances, increased mortality.

What may be less obvious to the caretaker is the cost of heat stress on reduced pig performance. Inconsistent growth rate and feed conversion, decreased carcass composition and quality, and reduced fertility all create production inefficiencies that result in economic losses for the industry estimated at nearly $1 billion (Pollmann, 2010). As such, understanding how to manage the barn environment and how to implement other strategies to mitigate heat stress can bring value to the operation.   

Physiology of heat stress
As temperatures rise, pigs will naturally employ strategies to maintain their core body temperature. Increasing blood circulation to the skins surface helps dissipate heat from their core to the environment. When temperatures reach a level where the heat transfer through the skin becomes ineffective, pigs rely on evaporation for heat loss by increasing respiration rate and panting as they lack the ability to sweat. Pigs will also voluntarily reduce feed intake and physical activity in effort to reduce metabolic heat production.

Through the response of shunting blood flow to the exterior, the pig reduces blood flow to the internal organs. Decreased circulation results in the weakening of the intestinal barrier and increased permeability (leaky gut) (Baumgard and Rhoads, 2013), ultimately leading to an immune response and further compounding the negative effects of the stress event brought on by elevated temperatures. It is also clear that these same heat events negatively impact muscle growth and metabolism, kidney health, and cardiovascular function.

Minimizing the effect of summer heat

Growing pigs
Optimizing air speed is a vital part of keeping pig comfortable. Target air speed should be around 350 feet per minute to optimize the cooling effect in tunnel ventilated barns. For naturally ventilated barns, stir fans and wind going across the barn can help achieve greater air speed. When environmental temperature approaches the skin temperature of the pig (92-96 degrees Fahrenheit), elevated airspeed becomes less effective at cooling the pig. In this situation, adding water to the pig's skin to facilitate evaporative cooling is important to alleviate heat stress.

Correct management of the sprinklers will support the effectiveness of heat loss. Having the sprinklers set to turn on at 18-20 degrees Fahrenheit above the set point and setting the run times for the sprinklers (two minutes ON: 15 minutes OFF) is optimal to allow the droplets time to evaporate off the skin of the pig and the environment and minimizes changes in humidity.

Check to see that fan louvers are clean and not excessively flapping. Dust or dirt can build up, reducing the efficacy of the fan, thereby decreasing ventilation rate and the airspeed across the pigs. Keeping them clean can allow for maximum air flow and more effectively cool pigs.

Evaporative cooling pads are commonly used on sow farms to decrease incoming air temperature. While cool pads are most effective in drier climates, proper management is critical to optimize performance regardless of outside humidity. Routinely check to see the pad is fully saturated and that the optimum air speed (350-400 FPM) is achieved.

Other management strategies should also be implemented to combat seasonal infertility. In lactation, feeding sows during cool parts of the day, or encouraging sows to stand multiple times can help encourage feed intake and thus better maintain body condition prior to weaning. Always supply fresh feed and keeping feed from spoiling in the feeders can also help with feed intake during lactation. If sows become heat stressed prior to farrowing, utilize water dripping equipment along with ample air movement to help reduce body temperature.

Conducting high-value tasks like breeding and estrus detection should be done early in the day to avoid negative impacts of temperature on pig behavior. If necessary, using commercially available gonadotropins at weaning can help shorten the wean-to-estrus interval as well as improve estrus behavior and detection.   

Heat stress research at Iowa State University
For some time, researchers at ISU have been interested in the physiological consequences of heat stress on pigs. Their goal is to gain a comprehensive understanding of the multisystemic consequences of heat stress so that appropriate, cost-effective interventions can be developed. Collectively, their work has helped establish that heat stress damages the gut and contributes to inflammation and immune activation associated with heat stress and may even decrease nutrient absorption. This is particularly problematic for animals that already have decreased food intake.

Heat stress also has broad impacts on metabolism and energetics and causes damage skeletal muscle, which leads to decreased meat quality, and to reproductive tissues, which leads to decreased reproductive efficiency. Some of their most current work is focused on a potential interaction of biological sex on heat stress as well as a consideration of other organ systems like the heart and kidney, the health of which is essential for an optimally functioning and growing animal. 

Source: Matt Romoser, Josh Selsby and Brett Ramirez, who are solely responsible for the information provided, and wholly own the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.

Mayorga, E.J., Renaudeau, D, Ramirez, B.C., Ross, J.W., Baumgard, L.H., Heat stress adaptations in pigs, Animal Frontiers, Volume 9, Issue 1, January 2019, Pages 54–61,

Pollmann, D. S. 2010. Seasonal effects on sow herds: industry experience and management strategies. J. Anim. Sci. 88 (Suppl. 3):9 (Abstr).

Baumgard, L. H., and R. P. Rhoads, Jr. 2013. Effects of heat stress on postabsorptive metabolism and energetics. Annu. Rev. Anim. Biosci. 1:311–337. doi:10.1146/annurev-animal-031412-103644

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