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Heat Stress in Sows

Sows laying down.
By: Nicole Gregory, Ph.D.
Monogastric Nutritionist
Grand Valley Fortifiers
As the hot weather of summer approaches, it is important to find ways to keep both ourselves and our sows cool. Pigs have a difficult time dealing with heat compared to other animals, since they cannot sweat and have limited ability to pant. This makes it difficult for the pig to dissipate heat and maintain a comfortable body temperature. If a pig is unable to release enough heat to regulate its body temperature, the pig will enter what is called heat stress. Susceptibility to heat stress is a problem for the modern sow, since she is larger, leaner and more productive (producing larger litters and more milk in lactation), which are all factors that increase the amount of heat that her body produces. These factors make it difficult for the sow to maintain her body temperature once environmental temperatures exceed her thermal neutral zone of 22⁰ C, which is worse in times of high humidity.

With temperatures on the rise and higher prevalences of heat waves around the globe, heat stress in sows is a true concern. When a sow is exposed to high temperatures, she will try to combat the environmental heat through reducing the heat she produces. To do this, a sow will decrease her feed intake to limit heat produced from digestion.

Additionally, she will reduce blood flow to places like the gastrointestinal tract and mammary gland to allow for more blood to flow to the periphery of the body dissipate heat. This reduction in feed intake and blood flow creates a negative effect on sow performance through decreased nutrient intake, which increases body condition losses and reduces milk production in lactation. It also creates inflammation and oxidative stress in the body, leading to leaky gut in the gastrointestinal tract (Liu et al. 2022). Additionally, heat stress can impact the reproductive performance of the sows, reducing the amount and quality of oocytes released prior to breeding, higher occurrences of anestrus, and longer wean to estrus intervals, all leading to lower farrowing rates and reduced litter size in the following lactation (Liu et al. 2022).

As the hot weather of summer approaches, it is important to find ways to keep both ourselves and our sows cool. Pigs have a difficult time dealing with heat compared to other animals, since they cannot sweat and have limited ability to pant. This makes it difficult for the pig to dissipate heat and maintain a comfortable body temperature. If a pig is unable to release enough heat to regulate its body temperature, the pig will enter what is called heat stress. Susceptibility to heat stress is a problem for the modern sow, since she is larger, leaner and more productive (producing larger litters and more milk in lactation), which are all factors that increase the amount of heat that her body produces. These factors make it difficult for the sow to maintain her body temperature once environmental temperatures exceed her thermal neutral zone of 22⁰ C, which is worse in times of high humidity.

With temperatures on the rise and higher prevalences of heat waves around the globe, heat stress in sows is a true concern. When a sow is exposed to high temperatures, she will try to combat the environmental heat through reducing the heat she produces. To do this, a sow will decrease her feed intake to limit heat produced from digestion.

Additionally, she will reduce blood flow to places like the gastrointestinal tract and mammary gland to allow for more blood to flow to the periphery of the body dissipate heat. This reduction in feed intake and blood flow creates a negative effect on sow performance through decreased nutrient intake, which increases body condition losses and reduces milk production in lactation. It also creates inflammation and oxidative stress in the body, leading to leaky gut in the gastrointestinal tract (Liu et al. 2022). Additionally, heat stress can impact the reproductive performance of the sows, reducing the amount and quality of oocytes released prior to breeding, higher occurrences of anestrus, and longer wean to estrus intervals, all leading to lower farrowing rates and reduced litter size in the following lactation (Liu et al. 2022).

Ultimately, heat stress decreases the performance of both the nurse and dry sows and therefore it is important to be able to recognize the signs of heat stress. Sows under heat stress will have a high amount of panting, reduce their movements, increase time lying down, lie farther apart from one another in group pens, increase water consumption, and reduce voluntary feed intake. There are some management strategies to reduce the impact of heat stress. This can include ideal ventilation management to allow for increased air flow throughout the barn or the rooms, avoid overcrowding for sows in group housed pens, using misters or sprinkling systems to help cool the sows through evaporation, in-floor cooling, and cooling mats for sows in individual crates. Additionally, being mindful of the heat produced from heat lamps or mats in the creep areas and adjusting the temperature as needed during elevated environmental temperatures.
While environmental changes are not always possible in every system, dietary management can also help sows manage during times of heat stress. Ensuring that all sows have unrestricted access to fresh, clean water is important throughout the year, but is especially important during times of increased temperatures, due to the increased requirements of water. Additionally, adjusting the feeding schedule to provide feed during the cooler times of the days (such as the early morning or evening) if possible, can help improve feed intake. It is also important to consider the amount of heat that is being created during digestion of the diet.

Providing energy from nutrients that produce a lower amount of heat during digestions, such as dietary fat, can ensure proper energy density of the diets during times of elevated heat in the summer. Ingredients that are high in fibre produce high amounts of heat when digested, however fibre is important for dry sows to ensure proper satiety, therefore it is important to balance fibre to provide satiety while minimizing heat production. High levels of crude protein can also produce larger amounts of heat when digested. It has been shown that reducing crude protein while maintaining ideal amino acid ratios through crystalline amino acid inclusion was able to reduce the amount of heat that is produced (Zhang et al. 2020). Additionally, providing increased levels of antioxidants, like vitamin E and selenium, can help reduce the impact of oxidative stress on the gastrointestinal tract that can occur during heat stress. Identifying the signs of heat stress in your sows and implementing strategies to help mitigate the effects, this allows sows to continue to be productive throughout the heat of the summer and all year round.

Contact your Nutritionist or Livestock Business Consultant today to plan your heat stress mitigation strategies.

References:
Liu, F. , W. Zhao, H.H. Le, J.J. Cottrell, M.P. Green, B.J. Leury, F.R. Dunshea, A.W. Bell. 2022. Review: What have we learned about the effects of heat stress on the pig industry?. Animal. 16:sup2.
Zhang, S., J.S. Johnson and N.L Trottier. 2020. Effect of dietary near ideal amino acid profile on heat production of lactating sows exposed to thermal neutral and heat stress condition. Journal of Animal Science and Biotechnology. 11:75.

This article was written for the Summer 2025 Swine Grist. To read the whole Swine Grist, click the button below.

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