Helping Sows Beat the Heat

Wednesday, July 23, 2025

Pigs Are Particularly Sensitive To Heat Stress

By Maude Richer-Lanciault, Swine Nutrition Manager, Western Canada, Trouw Nutrition

As summer temperatures arrive earlier and stay warmer for longer, heat stress is becoming a recurring challenge on pig farms across Canada. Warm, humid weather can compromise sow performance, especially with today’s hyperprolific sows. While we cannot change the weather, we can adjust our management and the sow’s nutrition to limit the impact of heat stress.

Sensitivity to heat stress

Pigs do not sweat, making them particularly sensitive to heat stress. To lose body heat, pigs redirect blood flow from the gut to the skin to dissipate it toward the environment. This shift can damage intestinal cells, reduce nutrient absorption, and open the door to pathogens (‘leaky gut syndrome’). When this happens, both feed intake and performance can be negatively impacted.

Over the years, the genetics and physiological composition of pigs has drastically changed, making pigs leaner with lower fat deposition. From 1991 to 2001, lean tissue has increased by 1.55 per cent, resulting in a 14.6 per cent rise in metabolic heat production (Brown-Brandl et al., 2004). With more internally generated heat, we need to adjust barn ventilation to keep pigs in their thermoneutral zone.

The thermoneutral zone is the temperature range in which pigs perform best. For sows, the ideal temperature is 18 C. Once temperatures rise above 23 C, feed intake will be affected as sows start to experience heat stress. At temperatures between 20 C and 30 C, sow feed intake can drop by as much as 23 per cent. Humidity also plays a role in heat stress; the temperature the sow will feel may be different when accounting for relative humidity. Sows in a barn at 26 C with 80 per cent relative humidity would be in heat stress danger, whereas those in a different barn with the same temperature and 70 per cent humidity would be in heat stress alert. This emphasizes the importance of controlling the barn environment.

Supporting sows through heat stress

1. Keep a close eye on the environment in the barn, including aspects like ventilation, cooling systems and heat pads for piglets. Strategies like drip cooling (applying water to the skin), combined with increased air speeds, can promote a cooling effect. Increased air movement is an essential part of this strategy because of the increased moisture in the room, but be mindful to avoid drafts on newborn piglets as they have a higher thermoneutral zone. Good air quality helps both the animals and staff.


2. Water should always be readily available, and also be of good quality. Before the summer heat, perform a water quality assessment to evaluate characteristics like minerals and microbiology. Water flow should also be evaluated at various water drinkers, and there should be sufficient water drinkers for all sows in group housing areas. Cool water also helps sows to more effectively regulate their body temperature.


3. Sows may eat less in the heat, so pay attention to their feeding patterns, and match this pattern to your feed allocation program. Offer lactation feed during cooler periods of the day, like early morning and late night. Keeping feed fresh and clean will encourage feed intake.

Nutrition combats heat stress

When sow feed intake decreases, milk production often suffers, leading to reduced piglet body weight gain. Your nutritionist can work with you to find the best approach for your barn during the summer months. Solutions could include adjusting the feeding program, including certain feed additives, or making shifts in diet formulations.

Several tools can adjust your feeding program during heat stress. For example, the NutriOpt Sow Model can calculate the target feed intake at different temperatures, evaluate the best feed density, and customize the program according to specific characteristics like environment, genetics, performance, and management. Adjustments to feed density can also support a lower feed intake during summer. For example, a specific adjustment of amino acid ratios with energy, protein level, fibre and other nutrients can maintain a balanced feed with a higher density. The overall goal should be to support the sows’ needs while creating less heat throughout the digestive process. Feed should nonetheless also be kept very palatable to stimulate feed intake.

Oxidative stress impacts high-producing animals, especially under challenging conditions like heat stress. The damaging impacts of oxidative stress can be reduced via antioxidants, which can be added to the nutritional program to offer support during heat stress.

In one research study, supplementation with a polyphenol blend increased sows’ reproductive performance, compared to a control group that only received vitamin E. It also increased lactation feed intake, numerically increased the number of piglets weaned, and increased litter weaning weight.

Polyphenols reduce lipid peroxidation before and during health stress by decreasing malondialdehyde (MDA) production. Given the study results, polyphenols may thus increase the antioxidant capacity in sow diets to improve piglet performance, while maintaining cost per piglet produced.

Several other additives are also available. For example, for leaky gut syndrome, antioxidants and osmoregulatory compounds like betaine can support gut integrity and help prevent the negative impacts of heat stress. Choose the additive that best fits the needs of your operation and offers the best return on investment.

Heat stress can take a real toll on sow performance. Given its large impacts on sow farms, adopting multiple strategies is the best way to mitigate negative effects. Practical farm strategies include ensuring access to cool, clean water, and maintaining ideal barn conditions, whereas feeding strategies include offering palatable and fresh feed, considering the inclusion of feed additives, and adjusting feed density. Your nutritionist can help fine-tune these strategies based on your specific situation so that your sows can maintain their productivity regardless of the heat. BP