With this summer’s heatwaves causing significant problems on farms and extreme weather becoming more commonplace, experts from the Pig Veterinary Society, AHDB, Red Tractor and the building and equipment sector for advice for producers to minimise the impact.
Why pigs are vulnerable
Pigs have no functional sweat glands – to cool down they rely on panting, contact with cool surfaces, reduced physical activity, shade-seeking, and evaporative heat loss (wallowing).
Their small lung-size relative to body mass, and a high metabolic heat production makes them especially vulnerable to heat stress, vets from the PVS explained.
“Experience suggests that fast-growing finishers, lactating sows and also older and heavier late gestation sows approaching farrowing are particularly vulnerable. When temperatures rise above the thermoneutral zone (18-25deg.C for grower-finishers, 15-22deg.C for sows – depending on relative humidity), pigs increasingly struggle to lose heat and may rapidly enter physiological distress,” PVS said.
Heat stress can result in mortality at the extreme, but other impacts include reduced breeding performance, and also reduced growth and carcase quality.
Advice to producers
Water
- Check all drinkers for flow; increase availability.
- Manage water system hygiene, especially open troughs, to maintain palatability
- Provide additional troughs for groups.
- Test mineral levels in natural water sources – periods of dry weather can change concentration with the potential to impact palatability
Ventilation & cooling
- Maximise airflow; open vents fully.
- Use fans, misters, or sprinklers where fitted. When used together these maximise evaporative cooling.
- Reduce stocking density so pigs can lie apart.
Feeding
- Feed early morning or late evening.
- Reduce daytime handling and avoid moving pigs in heat.
Breeding management
- Reduce early pregnancy loss:
- Avoid mixing/grouping sows immediately after service as heat increases aggression and stress.
- Keep early-gestation sows as cool and calm as possible for at least 35 days
- Compensate for reduced farrowing rates:
- Consider increasing numbers of females inseminated in predicted hot spells to smooth out any disturbance of downstream pig-flow.
- Support timely insemination:
- Use double insemination, first at onset of oestrus, second 24hrs later.
- Increase frequency of heat detection in hot periods – oestrus may be less apparent or delayed.
- Maximise oocyte quality and numbers:
- Ensure sows are on a positive plane of nutrition at weaning despite potentially reduced feed intake in heat stress. Review dietary specifications with a nutritionist, including supplements such as betaine and essential (n-3, n-6) fatty acids; consider dextrose supplement in post-weaning/pre-service interval
- Protect boar semen quality:
- Natural service: keep boars in the coolest housing available, avoid >30C if possible, and reduce mating pressure on boars. Note semen quality may be impaired for up to 45 days after a heatwave – one full cycle of spermatogenesis.
- Artificial insemination: Maintain strict AI semen storage temperatures (17C) and avoid transport delays.
Transport
Only transport pigs in a heatwave if it is essential to do so.
- Avoid moving or loading pigs in the heat of the day
- Never leave pigs in stationary vehicles. If a driver is stuck in traffic or another road incident contact the police and, if needed, DEFRA’s Rural Services Helpline (03000 200 301).
Outdoor pigs
- Provide shade, well-maintained wallows, and easily accessible cool drinking water.
- Ensure huts are well-ventilated, insulated and not facing direct sun.
- Whitewash may be applied to the exterior of huts to increase reflective heat loss, and arks can be positioned to face the wind.
Contingency planning (Red Tractor requirement)
Red Tractor requires pigs scheme members to have contingency plans in place to minimise the impact of extreme weather on pig welfare. These plans must set out the actions to be taken in relevant situations, including extreme heat.
All housing that relies on ventilation systems must have alarms and appropriate back-up provision in the event of system failure, and pigs on outdoor sites should be provided with facilities to minimise risk of sunburn, such as shaded areas and wallows.
Longer-term adaptation for UK climate change
Infrastructure
- Upgrade ventilation systems; consider automated climate control.
- Install permanent shade structures for outdoor herds.
- Add wallows, sprinklers, or misting systems.
- Engage with specialist buildings advisors when planning new-builds.
Breeding and nutrition
- Review boar housing and semen storage temperatures.
- Adjust lactation diets to support sow energy balance in summer.
- Discuss potential hormonal and micro-nutrient supplementation approaches with your vet.
- The use of hCG for sows after insemination may boost progesterone and oestrogen in the post-service period supporting implantation, and supplementation with B12 and folic acid has also shown benefit.
- Antioxidant or betaine supplementation during hot periods may support semen and oocyte quality.
Management
- Plan farrowings and services to avoid peak summer heat where possible. Plan increased inseminations to compensate for expected reduction in fertility.
Monitoring and training
- Use temperature/humidity sensors in buildings to enable better contingency and response planning.
- Train staff to recognise and respond to early signs of heat stress, and in specific skills including detection of sub-oestrus.
Additional information
- Avoiding Heat Stress in Pigs (AHDB). https://ahdb.org.uk/knowledge-library/avoiding-heat-stress-in-pigs
- Review: What have we learned about the effects of heat stress on the pig industry? https://doi.org/10.1016/j.animal.2021.100349 (open access)
- Red Tractor signposts scheme members to a range of industry guidance, including AHDB factsheets, in the ‘Where to Find Help’ section of the Red Tractor Pigs Standard.
- Some veterinary practices provide guidance.