Press release Study on heat stress in pigs results in heat plan
Simple measures such as more space per pig, antioxidants in the feed, misting systems, and extra fans in the barn alleviate the negative effects of heat stress on fattening pigs during hot summers. This is demonstrated by the doctoral research of Lotte De Prekel (Ghent University – ILVO): "When there is prolonged heat in a pig barn, don't look for a single miracle cure. It is the combination of several small management measures that can make a big difference for the animals."
The pig sector requested that a series of relatively feasible measures be tested during natural summers and during controlled "heat waves" in the barn.
De Prekel's doctoral work, supplemented by findings from the COOLPIGS project and literature research, has led to recommendations that have been summarized in a practical heat plan for pig farmers. The pig sector is now the first animal sector in Flanders to have such a heat plan.
Stress starting at 24°C but differences between pigs
In the doctoral study, more than 9,000 individual fattening pigs were observed. The researcher observed early signs of heat stress in all animals at barn temperatures between 24° and 27°C, temperatures that are easily reached in summer.
However, not all pigs appear to be equally sensitive to heat. Castrated males and heavier animals (>100 kg) are particularly sensitive and react at temperatures as low as 24°C. As temperatures rise to 27°C, the respiratory rate increases in all animals. Pig lines selected for growth rate (less muscle development) are more resistant to heat than lines selected for carcass quality.Sows are most at risk of heat stress in the farrowing pen, during farrowing, and when producing milk for their piglets.
Lotte De Prekel: “Heat stress is a condition in which the body can no longer maintain its temperature. The problem is becoming increasingly common in farm animals due to rising global temperatures. Pigs are mainly kept in stables and are particularly vulnerable to heat because they are unable to sweat. Like humans, they need to maintain their body temperature as constant as possible. When their environment is too warm—especially when combined with high humidity—they find it difficult to release excess heat. They start panting and seek out cooler spots in the pen.
When they are unable to cool down sufficiently, they eat less, grow more slowly, and their immune systems can weaken. Heat stress therefore not only has a negative effect on their well-being, but also on their health and growth performance.
Scientifically based, effective heat measures
A combination of small interventions can make a big difference, especially for companies where the basic conditions are not optimal.
Meer ruimte per varken
Fewer pigs per pen means greater distance between pen mates and more space to lie on the cool floor. This allows them to cool down better during hot periods.
With 25% more space (from 0.8m² to 1m²), their body temperature rises less during a heatwave (+0.1°C instead of +0.2°C). This difference seems minimal, but in the test barn there are groups with different densities in the same compartment. If the number of pigs in all pens decreases, this cooling effect increases further, because the animals themselves are also a source of heat. If the space per pig is further increased by 50% (to 1.2m²), their growth also increases by 75 grams per day.Antioxidants in feed
Just like humans, pigs eat less during hot days to inhibit internal heat production through digestive processes. Digesting protein creates the most body heat, but trials with a high-fat, high-energy feed and lower protein content showed no improvement.
Antioxidants can reduce cell damage in the digestive system caused by heat stress, according to trials. Adding the antioxidants vitamin E, vitamin C, and organic selenium to the feed causes the pigs to grow slightly more (+34 g/day) with the same feed intake, and the meat quality improves slightly.
Lotte De Prekel: “We find the administered selenium and vitamin E in the meat, which even has added value for the consumer. European consumers often have a selenium deficiency (40 micrograms/day, while 60 to 70 micrograms/day is recommended). Eating 100g of this meat with extra selenium provides an increased intake of 10 micrograms/day. This strategy is therefore beneficial for both humans and animals.
Air cooling
Within the umbrella VLAIO project COOLPIGS, ILVO and Ghent University also tested technical solutions for pigsties. High-pressure misting lowers the temperature in the pigsty by 2.5°C and ensures that the pigs breathe more calmly (breathing frequency decreases by 8%).
For sows in the farrowing pen, better air mixing via extra fans provides cooling: here too, we see a clear decrease in their respiratory rate by 14%.It is also important to keep the air entering the barn via the air inlet as cool as possible. An air inlet on the shaded side reduces the temperature of the incoming air by 6°C. If sunlight cannot be avoided, the farmer can create shade using a canopy, fence, or plants.
Heat plan for pig farming, with VLIF support
For some time now, the pig sector has been expressing its need for knowledge about concrete, effective measures to tackle heat stress in pigs. The research results of the PhD and the COOLPIGS project, together with results from literature research, have therefore been clearly compiled in a concrete Heat Plan for Flemish pig farming. This provides pig farmers, transporters, and slaughterhouses with practical and economically feasible tools to reduce heat stress in fattening pigs.
With this plan, the pig sector is the first animal sector in Flanders for which the effective heat measures known to date have been compiled. It is being widely disseminated through the pig desk. VLIF subsidies support the implementation of measures from the heat plan for the pig sector. The results of this research have been included in the list of sustainable and future-oriented business investments of the Flemish Agricultural Investment Fund (VLIF). Farmers can, for example, apply to the VLIF for financial support for the installation of additional fans as a measure against heat stress in sows in their farrowing pens.
Lotte De Prekel's PhD thesis was defended on June 19, 2025.
