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Heat Stroke

This disease affects all pigs. The key clinical signs include a high respiratory rate; distress; rectal temperature of 43°C.

Background and history

Extreme temperatures and water shortages take their toll on pig herds in particular, with heat stress and heat stroke being prominent causes of weakness, diarrhoea and acute distress. Droughts result in restricted water use across all agricultural businesses and in swine herds, water shortages can be catastrophic – continuous access to clean water is critical for pig health. Wallows (mud baths created through pumping water into shallow mud areas) also provide pigs with some relief from the heat but water use restrictions can prevent the maintenance of such areas.

According to advice published on the website of Western Australia’s Department of Primary Industries and Regional Development, “Most animals can transfer internal heat to the outside of the body by sweating and panting – these are the two most important tools for the maintenance of body temperature and form their inbuilt evaporative cooling system. However, pigs do not sweat and have relatively small lungs. Due to these physiological limitations and their relatively thick subcutaneous fat, pigs are prone to heat stress.”

Responsible use of water and keeping your pigs cool are essential to maintaining productivity and welfare in your herd.

This usually occurs where ventilation has failed or in extremely hot weather.

Clinical signs

When a pig’s internal temperature increases, it reaches a point where it can no longer increase moisture loss through increasing respiration and sweating – the ‘heat stress emergency’ point. The animal may pant harder but without relief; this cycle can lead to death. In cases in which heat stress occurs only for a short period of time (two to three hours), no lasting harm has been observed in most individuals.

  • Respiration increases in intensity (panting).
  • Lethargy when moving.
  • Pig reduces its feed intake to slow the internal heat of digestion (sensible heat) being produced.
  • Reduced growth in feeder pigs.
  • Reduced milk production in lactating sows.
  • Loss in weight.
  • Diarrhoea.
  • Increased water consumption.
  • Increased urine output.
  • Muscle trembling and weakness.

Diagnosis

Knowledge of the environmental factors and clinical signs.

Causes

  • High temperatures.
  • Exposure to sunlight.
  • Combined with high humidity and poor ventilation in indoor housing.

Prevention

Indoor housing and ventilation

  • Ensure ventilation units are working correctly by performing maintenance checks as soon as temperatures breach thermoneutral zones and ensure that any issues are corrected immediately to avoid having to take emergency measures.
  • Ensure that stocking densities are reduced during periods of extreme heat if ventilation cannot be improved.
  • Do cover any ceiling windows where sunlight shines directly into pig pens.
  • Insulate inner barn rooves and use lighter, reflective colours externally to reduce heat absorption and radiation into the barn.
  • Provide some barren sections in resting areas that are not covered in straw as it has been proven that pigs will seek barren areas during periods of high heat in order to keep cool. Do, however, maintain straw in pens as it is important for gut fill.
  • Producers using bedded packs should ensure that the manure pack is kept to a minimum depth, and dry. Deep, damp manure packs start to compost and release heat and moisture. As the stomach is the heat generation centre, giving the animals minimal bedding allows them to transfer heat to the cooler floor below when they lay down.
  • Use a backpack sprayer in confined conditions, such as show pens, as the mist will cool the pig without overly wetting the bedding.
  • During periods where water use is not restricted, use a misting system low down in the barn as evaporating water has a cooling effect on pigs’ skin.

Outdoor housing

  • Provide access to plenty of shade – artificial (larger arcs and canopies) or natural (trees/woodland). Uninsulated aluminium or bright galvanised steel are perfect for constructing artificial shade canopies.
  • Paint arc roof white and/or cover in branches or foliage to reflect light.
  • During periods where water use is not restricted, use sprinkler systems around housing and create wallows.
  • Apply sunscreen where mud baths and shade cannot be provided.

To keep water cool and clean... keep water storage and water troughs in the shade, and use blocks of ice or frozen tubs of water to bring the water temperature down and reduce evaporation.

Piglets

Piglets need continuous access to water at two weeks old and, if left in direct sunlight or in poorly ventilated barns can suffer heat exhaustion, potentially resulting in mortality.

Sows

Breeding herds are particularly susceptible to an array of reproductive issues, including decreased farrowing rates, smaller numbers born per litter, a reduced number of piglets born alive per litter, higher embryonic deaths during early gestation, a larger number of stillborn piglets and miscarriages. Heat stress is also responsible for increased mortality among sows.

Boars

Heat stress and dehydration in boars can result in lethargy and reduced libido, increased irritability and aggression, and can degrade semen quality.

The same measures must be taken for the boars as for sows during periods of high temperatures, ie provision of wallows and shades, ensuring adequate resting space, and provision of ample fresh, cool water.

Protein

In prolonged hot weather, consider feeding pigs the lowest safe level of protein, ensuring the correct essential amino acid balance is maintained. The higher the nutritional protein consumed, the more water pigs require to stay hydrated, therefore reducing protein intake will reduce water required and reduce risk of dehydration.

Treatment

  1. Use a cool, wet towel on the neck and back of a pig and change the towel regularly to ensure it is having the desired cooling effect.
  2. Consider putting diluted vinegar on the skin as it evaporates quickly, removing heat. Once cooler wash off the vinegar if you wish.
  3. Dribble cold water into the rectum of the affected animal using a flutter valve.
  4. Feed electrolyte rebalancing solutions to seriously affected pigs.

One top tip: Do not use cold or freezing water to cool pigs down if doing so directly – use tepid water as the shock of cold water has been known to kill pigs.