Expert tips on reducing heat stress in pigs

Hot weather can severely curtail growth in finishing pigs by suppressing their appetite and also reduce farrowing rates in the breeding herd by as much as 25%.

With UK temperatures now getting to 32C in some areas of the country in recent years, pig producers are being advised to take measures to avoid heat stress for animal welfare and to avoid performance loses.  

Debbie James spoke to Angela Cliff, knowledge exchange manager (central) at AHDB Pork, for advice on reducing heat stress in indoor and outdoor units.

See also: Guide to biosecurity measures to keep pigs disease-free

1. Water

Make sure there are sufficient drinkers in each pen, that they are all working properly and delivering clean water. Monitor flow rates so the pigs have the opportunity to get water when they need it.

2. Ventilation

Fans should be cleaned and maintained regularly and checked to ensure they are working properly either between batches or, if this is not possible, at least quarterly.

If you have changed to a batch system from continuous production, ensure there is enough fan capacity to cope with the heat produced in the later stages of finishing.

Top tips for ventilation

  • Check the temperature alarm weekly
  • Use a smoke plume to check how air is moving. Smoke should immediately disperse with the air
  • Consider using supplementary fans for large pens that rely on natural ventilation
  • Ensure arcs in outdoor systems are well insulated – during hot periods open back vents to improve ventilation
  • Painting arcs white will reflect sunlight and keep accommodation cooler

3. Wallows

All paddocks should have good, well-managed wallows with mud the consistency of thick emulsion; this can provide pigs with a layer of mud on their body to reduce sunburn.

Allow enough wallowing space for twice the number of pigs that have access to it, enabling the more submissive animals to use the wallow.

Top tips for wallows:

  • During periods of little or no rainfall, replenish the wallows with water every day
  • To prevent pigs from drinking the dirty water, offer a separate supply of clean water for drinking
  • Provide pigs in indoor units with areas of wet concrete or misters during hot periods

4. Shade

Sunburn is common in early summer and can cause pregnancy failure, pain and stress.

Outdoor units can prevent this by providing sufficient shade so pigs can move out of direct sunlight.

Indoor units may also require outdoor runs or the open sides of buildings to be shaded, if the sun is falling directly on to the sows or growing pigs

5. Consider changing feeding patterns

Ad-lib feeding can be helpful on outdoor systems as it allows feeding during cooler periods of the day.

Where feeding to appetite is practised, indoor units may decide to change their working hours during hot spells.

This allows the most susceptible animals, specifically lactating sows, to be fed during the cooler hours of the day.

6. Heat stress and its impact on different pig groups


Hot weather can have a detrimental impact on the quality of boar semen for many weeks with the most significant effect usually seen about three-to-five weeks after a hot spell.

During these periods, be extra vigilant with checking for returns – check semen quality for up to eight weeks after the last period of heat stress. Boars will not work in hot conditions and encouraging them to do so is likely to increase heat stress. Carry out all artificial insemination at either end of the day.

Sows post-service

Sows are most susceptible to heat stress seven to 14 days post service.

Keep sows cool with shades, wallows and sprinklers, and by ensuring ventilation systems are working efficiently.

Dry sows

Heat stress can bring about a deficiency of the hormones needed to support pregnancy so, where possible, make an area of wet concrete available for sows to lie on.

Don’t force sows to lie in the sun or on warm straw bedding, and provide shade curtains if sunlight is streaming into the pen.

Heat stress can also impact on the performance of litters as finishing pigs because pigs gestated by heat-stressed sows have been shown to have a higher body temperature throughout their life.

This results in more energy needed for maintenance, lower protein deposition and higher fat deposition, all of which will cause the feed conversion rate to deteriorate.

Lactating sows

To help keep sows cool, it may be helpful to wet the sows’ necks with cool water but ensure piglets do not get wet.

A supply of cold supplementary water when feeding is helpful.

Grower and finisher herds

To minimise or avoid performance drops, reduce the stocking density where possible so that pigs can lie away from each other.

Use foggers or misters if necessary.

What is heat stress?

Heat stress is caused when a pig’s body temperature rises above certain limits.

If the pig cannot cool itself sufficiently it will collapse and, in the most severe cases, heat stress can lead to death

The threshold temperature for heat stress is lower than many producers might think.

An AHDB-funded PhD study at Leeds University found outdoor sows responded when the ambient temperature reached 18C; extensive indoor systems may also behave in the same way.

But the optimum temperature for pigs varies according to the level the pig is starting from. If the pig is used to a much lower temperature then 18C may be too high.

Case study

John Theobold, Rattlerow Farms, East Anglia

Shade helps improve conception rates for outdoor breeder

A large scale outdoor breeder has improved sow conception rates by about 5% during hot periods, with no reduction in pigs born alive, since providing shades as protection from the sun.

John Theobold, outdoor production manager for Rattlerow Farms, commissioned bespoke mesh shades to cover areas between pig huts on the company’s seven 600-sow units in East Anglia.

There are 25 shades measuring six metres by five metres at each site.

Mr Theobold says the £80 cost of each shade was quickly absorbed by improved conception rates.

“With an outdoor pig farm, each year and season are unique, but since we have used shades we have had fewer fertility issues,” he observes.

“It might be coincidence, but we have seen a 5% or so improvement in sow conception in the hotter periods with no drop in born alive.”

The shades were initially provided to create an area where pigs could lie out of direct sunlight to avoid issues with sunburn and to help with general pig well-being.

“We are fortunate that we have very dry and sandy sites, but it means we can’t reliably make wallow holes. Shades offered an alternative solution,” Mr Theobold explains.

The shades are made from mesh and suspended between huts to minimise risk of wind damage.

The dry sow huts are six metres long and the back doors open to allow for good movement of cooler air during the summer months.

The shades hang on an elevated lifting frame fixed to the hut and these have three pulling points.

Simple baler twine is used to pull the shades tight between the huts, not only providing a shaded area, but the cooling temperature in the huts too.

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