What temperature is too hot for pigs?

Q: Can a pig overheat?

Despite the well-known saying, pigs dont actually sweat (aside from their snouts) and can struggle to maintain their body temperature. As a result, overheating in outdoor pigs is a key health and welfare concern, and can affect growth rates, fertility and, in severe cases, can lead to death.

Q: How do you cool down an overheated pig?

Cool water helps reduce the pigs internal body temperature, as well as replace water lost from elevated respiration during periods of heat stress. Provide market hogs with plenty of access to water.

Today’s modern pig genotypes produce considerably more heat than their predecessors.

Table of Contents Show

Why are pigs so sensitive to heat stress?
What does current research say about heat stress?
Consequences of heat stress on the performance of pigs
At what temperature and humidity do pigs get heat stressed?
Recommended management tools to reduce heat stress
Background and history
Clinical signs
Indoor housing and ventilation
Outdoor housing
How do I know if my pig is too hot?
Are pigs sensitive to heat?
Can a pig overheat?
How do you cool down an overheated pig?

A review of pig heat and moisture production by Brown-Brandl et al. (2003) suggested that new genetic lines of pigs produce nearly 20% more heat than their counterparts in the early 1980s. This trend is likely to have continued in the years since this review was conducted and heat production could be a further 10% higher again.

In this article we share some useful tools to determine when pigs become heat stressed and also provide recommendations to minimise production losses as a result of heat stress.

Why are pigs so sensitive to heat stress?

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. The two obvious symptoms observed when pigs are exposed to heat stress are increased respiration rate and loss of appetite. The latter reduces internal heat production. If heat stress continues, pigs start to drink excessive amounts of water (increasing loss of electrolytes) and accumulate acids produced within the body (causing a loss of acid/base balance). This may eventually result in diarrhoea or death in severe cases.

What does current research say about heat stress?

A recent publication by Pearce et al. (2013) examined what happened to the intestinal structure when pigs were exposed to heat stress. The research showed that exposure to 35°C for 24 hours significantly damaged the intestinal defence function and also increased plasma endotoxin levels. The authors explained that when pigs are exposed to heat stress (even for as little as two to six hours) their intestinal defence systems are significantly compromised and this provides opportunity for infection as pathogenic bacteria can invade the body more easily. Therefore, heat stress can create secondary infection if sanitary conditions are poor.

Consequences of heat stress on the performance of pigs

Bigger pigs are more prone to heat stress and the reduction in growth performance is greater than for smaller pigs.

Figure 1 shows the magnitude of performance loss in 25, 50 and 75 kilogram (kg) pigs when ambient temperature was increased from 14°C to 35°C. Average daily gain (ADG) starts decreasing when 75kg pigs were exposed to temperatures above 23°C, while for 25kg pigs ADG starts to decrease when exposed to temperatures above 27°C.

Figure 2 shows critical temperatures at various body weights — this information can be used as an index for the temperature management of different sheds housing varying age groups of pigs.

At what temperature and humidity do pigs get heat stressed?

Ambient temperature (as well as humidity) contributes to heat stress and pigs generally develop heat stress at much lower temperatures when the humidity is high. Iowa State University recently released a heat stress index chart (Figure 3) which can be used as a decision tool for implementation of management strategies to reduce heat stress. The chart shows that an average humidity of 30% coupled with temperatures higher than 28°C will significantly affect intestinal health and performance of grower-finisher pigs (conditions regularly experienced during a Western Australian summer). The temperature tolerance is lower for breeding herds.

Recommended management tools to reduce heat stress

Increase ventilation and airflow and regularly check cooling system is in good working order (for example spray cooling).
Reduce stocking density if possible.
Maintain drinking water temperature as low as possible (around 10°C is ideal but difficult to achieve).
Avoid feeding between 10.00am-4.00pm (the hottest period of the day).
Supplement electrolytes and antioxidants through the water supply.
Increase dietary energy density.
Minimise excess non-essential amino acids and fibre (minimising intestinal fermentation and therefore heat production).
Increase availability of antioxidants through the diet such as vitamin E and betaine.

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.

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.

How do I know if my pig is too hot?

Overheating can cause your pig to pant rapidly and excessively, drool thick, rope like saliva, the eyes may have a glazed over look to them and obviously may be excessively thirsty. His gums may become very dry and even a bit crispy from dehydration.

Are pigs sensitive to heat?

Pigs are more sensitive to heat than other animals because they can't sweat. Thus, high temperatures can lead to heat stress, which causes poor performance.

Can a pig overheat?

Despite the well-known saying, pigs don't actually sweat (aside from their snouts) and can struggle to maintain their body temperature. As a result, overheating in outdoor pigs is a key health and welfare concern, and can affect growth rates, fertility and, in severe cases, can lead to death.

How do you cool down an overheated pig?

Cool water helps reduce the pig's internal body temperature, as well as replace water lost from elevated respiration during periods of heat stress. Provide market hogs with plenty of access to water.