Heat stress in pigs is an increasing concern in modern livestock production, especially in regions facing more frequent and prolonged heatwaves. High temperatures combined with elevated humidity can severely affect pig welfare, growth, reproduction, and feed efficiency, while increasing mortality risk.
To address this, the CoolPigs project, supported by the Flemish Government through VLAIO (Belgium), developed a Heat Plan for Flemish pig farmers and an online Temperature-Humidity Index (THI) Tool. These resources provide practical and science-based guidance to anticipate, assess, and mitigate heat stress in pig herds.
The THI Tool: Predicting Heat Stress Risk
The THI Tool – available here, enables farmers to input barn temperature and humidity for an immediate heat stress risk assessment. If humidity measurements are unavailable, a standard value of 60% can be applied. Using established THI thresholds, the tool predicts when pigs are likely to experience physiological strain—a more reliable approach than relying on temperature alone.
Heat Sensitivity Across Pig Categories CoolPigs research revealed differences in heat tolerance:
- Heavy finishing pigs (>80 kg), especially barrows, show increased respiration at 24°C (60% RH) and rising rectal temperature at 27°C.
- Gilts tolerate slightly higher temperatures but experience stress from 28°C onward.
- Lactating and late-gestation sows are highly sensitive due to increased metabolic heat from milk production or foetal development. Genetic selection for high productivity has improved performance but reduced resilience to heat.
Strategies to manage heat stress
The tool differentiates between different types of measures to lower heat stress.
A first set of strategies is related to feeding and water management. The following strategies are suggested: Feeding adjustments: Offer smaller, more frequent meals during cooler periods to limit heat from digestion.
- Diet composition: Lower crude protein slightly during hot periods under expert guidance.
- Water access: Ensure unlimited access to fresh, cool water; check drinker flow rates. Chilled water (<15°C) boosts sow feed intake and milk yield.
- Water quality: Test regularly as heat promotes bacterial growth.
- Additives: Electrolytes and vitamins can help but have limited effect compared to structural measures.
A second set of key actions is related to housing and environment, such as:
- Improve ventilation with fans placed 1.6–1.8 m above the floor, activating automatically from ~25°C.
- Reduce solar heat via shading, reflective coatings, or UV films.
- Use insulation and light-coloured roofing to maintain stable indoor temperatures.
- Lower stocking density; send heavy pigs to slaughter earlier in summer when possible.
More long-term solutions in the housing include heat exchangers, floor cooling, misting, pad cooling, and integrated climate control systems. CoolPigs provided performance data from commercial farms for informed investment decisions.
Besides this, also behavioural and managerial measures can be taken. For example, avoid moving or mixing pigs during peak heat hours. Handle calmly to limit stress and provide clean, dry lying areas without overcrowding in shaded spaces.
Pigs can suffer heat stress during transport at temperatures as low as 22°C. Best practices include loading during cooler times, reducing density, minimizing handling, ensuring ventilation, and applying cooling measures in lairage areas.
Conclusion
The Flemish Heat Plan encourages a proactive approach that integrates short-term adjustments with long-term improvements to safeguard pig welfare and farm productivity under rising temperature challenges.
Reference:
De Prekel, L., Van den Broeke, A., Aluwé, M., & Maes, D. (2025, June 23). Hitteplan voor de Vlaamse varkenshouderij. Coolpigs-project. Vlaams Agentschap Innoveren en Ondernemen (VLAIO) (VLAIO-LA, HBC 2019.2877). Retrieved from https://www.varkensloket.be/Coolpigs
