Sunburn and Heatstroke/Heatstress

Author: Mark White BVSc LLB DPM MRCVS
Reviewed: Mark White BVSc LLB DPM MRCVS 2016
Published: 2003

During a warm dry spring and summer, the two separate conditions of sunburn and heatstroke tend to get linked together and whilst these are undoubtedly instances where the two conditions occur together they are distinctly different in their cause, development and consequences.

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Fig 1 : Gilts recently delivered have first exposure to sunlight in early Juneresulting in severe erythema typical of sunburn.


Fig 2 : Outdoor sows in summer and late spring are susceptible to sunburn.


Fig 3 : Thick mud wallows can provide an effective screen to sunburn although it is more effective when completely covered.


Known in medical terms as hyperthermia - occurs when the core body temperature rises and the normal control mechanism fails to reduce it.  The pig is a relatively poor controller of its own body temperature, not sweating (other than from the snout) and if it is unable - due to environmental conditions - to wet its skin and thus allow latent heat of vaporisation to cool it (the exact process that occurs with sweating in man) it cannot lose heat from the skin.  Even if able to wet the skin (wallowing, playing with water nipples etc) if humidity is very high, the water will not evaporate and thus there will be no cooling (A similar situation occurs in a sauna in man).  In practice, in temperate climates, humidity is rarely a major problem but can occasionally be an issue.

Pigs also generate a lot of heat - a bacon pig being roughly the equivalent of a 1KW bar heater and so confined buildings contain a lot of heat that needs to be removed. Thus inevitably heatstroke occurs both indoors and outdoors.

In the absence of wallowing or wetting, the only methods available to the pig to avoid over-heating are moving to cooler areas - such as where there are draughts or shade - and panting.

Whilst the ultimate consequences of heatstroke are disastrous i.e. death, early signs would include increased respiratory rate, attempts to lie on their sides, away from other pigs, lying in dunging passageways and excessive playing with water.  An increased respiratory rate leads to more water loss (i.e. the cooling process) and thus dehydration may become an issue possibly leading to salt poisoning/water deprivation syndrome in growing pigs.

In the breeding animal overheating can interfere with the reproductive cycle and delay or suppress the onset of oestrus especially in gilts

Measures that are necessary to avoid overheating or heatstroke will depend upon the age of the animal at risk and the accommodation available.  In general, however, the following points are valid:-

1) Provide adequate insulation in buildings.

2)  Enure fan capacity and controls are sufficient to hold the room temerature at no more than 4°C higher than ambient temperature.

3) Fit and test alarm systems that warn of rising temperatures - by law alarms must be tested weekly.

4) Ensure fail safe systems are fully functional.

5) Provide drip lines, mist sprayers, wallow areas to aid cooling but can lead to hygiene problems and raise humidity beyond saturation point.

6) Provide readily available high flow rates of water (minimum 0.5 litres per min rising to 1.5-2 litres for lactating sows).

7) Reduce stocking levels.

8) In extreme weather, wet passageways in buildings or even spray building roofs with water.

9) Reduce levels of bedding to encourage heat dissipation. This should include removal  of deep straw bedding with composting underneath which not only reduces heat dissipation but acts as a hot bed increase lying temperatures

With its high bodyweight to surface area ratio, the adult is particularly vulnerable and other features of overheating in the longer term include:-

  • Reduced lactation feed intake and hence reduced milk supply.
  • Embryo death leading to returns to service or very small litters.
  • Abortions.
  • Reduce boar sperm volume and quality and hence lower fertility/litter size.
  • Suppression of oestrus

In a hot summer period the impact of hot weather on one typical 500 sow breeder weaner unit over a 4 week period was recorded as:-

a) 6 sows died of heat stroke around farrowing

b) Farrowing Rate depressed by 11% giving a shortfall of 11 farrowings in October.

c) Depression of litter size in October by 0.9 pigs/litter = 76 piglets.

Therefore a shortfall of piglets produced in the autumn was approximately 200 piglets @ £40/pig (cost of production plus lost profit opportunity) = £8000.  The impact of reduced weaning weights in piglets reared in hot weather must be added to this.

In growing pigs in very hot weather, appetite can reduce by 50% with the effect of totally stalling growth.


Sunburn that can lead to heat stroke in itself - is a distinctly separate condition of obvious cause.  It is not restricted to outdoor pig production.  It tends to occur more commonly in early summer (May/June) as a result of the first exposure to strong sunlight since the winter and, in a mild form, reddening of the skin is all that is seen but, in severe cases, blistering can occur and when the back is severely affected the pig will adopt a characteristic pose with the back distinctly dipped and walking on the front knees.

Apart from the obvious pain and discomfort that sunburn produces, in some cases, it can lead to pregnancy loss (returns to service or abortion) or a failure to be served in an unsupervised regime.

It is important to remember that outdoors, water wallows will not protect against sunburn (children get sunburnt playing in the sea or in swimming pools).  To be effective, the wallow must provide a thick coating of mud over the body.  Shading is an alternative but litter desertion can be a major problem if used in a farrowing area.

Where pigs have become severely sunburnt shade must be provided and application of an emollient cream or 'pig oil' may ease discomfort and aid healing.  In severe cases non-steroidal anti-inflammatory painkillers are indicated on welfare grounds.

Sunburn should not be confused in outdoor situations with photosensitization normally precipitated by exposure to certain plant toxins present in eg. parsnips, carrots, rape and oats.  The appearance can be similar to severe sunburn.


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