Recognize, understand, avoid heat stress in sows, piglets and fattening pigs

Because pigs have almost no sweat glands (only on the trunk disc), they cannot sweat. Thus, they lack an important regulatory mechanism when the heat increases. By panting with their mouths open, the animals try to generate evaporative cooling via the liquid evaporating in the pharynx in order to cool down their organism. Panting is when the animals' respiratory rate leaves the normal range. Sows and fattening pigs breathe an average of 15 to 20 times per minute, while boars only breathe 10 to 15 times. For farmers, breathing rate is a good indicator of heat stress in the herd. With increasing heat, the water requirement of the animals therefore also increases.

Pigs reduce feed intake during heat stress. The digestive and fermentation processes in the gastrointestinal tract convert about 25% of the energy contained in the feed into heat. To reduce this waste heat, sows, for example, eat about 100 g less feed per day from temperatures of 21°C with each degree further temperature rise. At 30°C, this already corresponds to a reduction in the amount of feed consumed of almost 1 kg.

If the temperature in the stall rises, the blood flow to the skin increases due to a widening of the blood vessels. In this way, the animals release more body heat to their environment in order to cool themselves. However, this sensible reaction of the metabolism has an undesirable side effect: the detour of blood to the outer areas of the body (e.g. the legs) can lead to an undersupply of nutrients and oxygen to the intestinal cells. There is a risk of a deficient supply to the stomach and intestines. As a result, the digestive process slows down.

The dilatation of the blood vessels is also a reason why the pigs try to dissipate heat to their environment by lying on a cool surface. The so-called lying down cooling is a central behavior of heat-stressed pigs, which serves to regulate the body temperature. Lying down on metal slatted floors allows them to dissipate heat better than lying on concrete surfaces or plastic slats. Pigs also now prefer to wallow on damp ground to cool off.

High outdoor temperatures are the main cause of heat stress. However, body heat generated during digestive processes puts additional stress on the organism. There are major differences in the components that should be taken into account when designing feed rations.

While only 14% of the energy contained in fat is released as heat during digestion, around 25% of the energy in the feed is lost as heat in the case of starch and as much as 38% in the case of protein. This additionally heats up the animals' bodies. It is therefore advisable in spring and summer to reduce the protein content of the ration to the minimum technically necessary and at the same time to obtain the energy rather from feed fat, i.e. to increase the fat content. By evaluating the energy of the ration on the basis of net energy (NE), these aspects are taken into account by additionally including heat losses due to escaping body heat in the evaluation of the feed components - in contrast to the convertible energy, which only takes into account losses from feces and urine. Appropriately protein-reduced, highly digestible feeds are also optimized for praecaecal digestible amino acids. Finally, L-carnitine can be added to increase energy utilization in the feed.

A balanced fiber content in the feed is also important. Fiber keeps digestion going and provides additional energy in the form of short-chain fatty acids through fermentation in the large intestine. This also produces some waste heat. By promoting intestinal peristalsis, fiber nevertheless helps to counteract the slowdown in intestinal transit that threatens to occur in hot conditions. The fermentation capacity of pigs increases with age. For this reason, sows are also able to digest high fiber contents of 6% and more well.

To prevent heat stress-related fertility problems in sows, suitable diets should contain high levels of antioxidant substances and vitamin E. Endotoxin binders (e.g., clay minerals such as bentonite) can bind toxins, preventing them from entering the bloodstream. B vitamins can also help strengthen the immune system. In this way, oxidative stress can be reduced.

Finally, it is recommended to adjust feeding management to counteract heat stress:

• Make sure to offer the feed in more, but smaller portions. In this way, you provide targeted feed stimuli and take into account the animals' reduced appetite.
• Move feeding times to the cooler morning and evening hours, when the animals are more willing to eat. Avoid feeding large amounts of feed in the afternoon. This is when barn temperatures are highest.
• Bacteria and yeasts feel particularly comfortable at warm temperatures. Pay special attention to feed hygiene in summer and clean troughs regularly. If the feed stands in the lines and troughs for too long, feed residues begin to ferment, which reduces the acceptance of the feed.

Water is rightly considered the most important feed. This is all the more true when temperatures are high in spring and summer. Adapted watering management must take account of the pigs' increasing water requirements.

Table 1

Table 1: Water requirements of pigs in different housing stages at temperatures of 20°C. At temperatures of 30°C and more, the requirement can double. (mod. according to DLG Leaflet 351: "Drinking Technology for Pigs"; © Deutsche Tiernahrung Cremer).

You should ensure the supply of the animals with a drinking technique adapted to the husbandry section. Pigs are sucking drinkers. This means they prefer to take up water from open areas. Water troughs and basin drinkers are therefore particularly suitable for the daily supply. If the installation height is adapted to the animals and the flow rate is set correctly, drinkers that have to be taken into the mouth (e.g. nipple drinkers) are also suitable. Check the water flow and the functionality of the drinkers regularly.

It is imperative to check the water annually for its properties and ingredients. Increased mineral content leads to deposits in the pipes. This prevents unhindered flow and promotes the formation of a biofilm. Both of these factors noticeably reduce the acceptability of the water.

• Request a drinking water check, for example, in our LUFA testing tool to check the water quality on your farm.

Optimal temperature management starts with the construction of the barn. An orientation along the north-south axis provides many advantages. The barn roofs thus offer little surface for the sun to attack and the buildings heat up less quickly. Light-colored roof coverings, frosted glass windows on the south side and good insulation also keep heat out. Intensify sun protection by planting shade trees and shrubs outdoors.

The heart of climate management in the barn, however, is the ventilation and exhaust systems. Modern ventilation systems can be used to regulate air exchange and indoor temperatures. The intake points for the supply air should ideally be located on the shady north and north-east sides. Ventilation control requires a delicate touch: on the one hand, farm managers must ventilate and cool their barns during the hot months, and on the other hand, they must avoid drafts. While the air speed should not exceed 0.2 m/s in winter, it can be increased to 0.4 m/s in summer for fattening pigs. Otherwise, there is a risk of stress in the stock, as excessive temperature fluctuations between day and night mean stress for the animals. This in turn can promote the occurrence of cannibalism.

Spray cooling can cool down the ambient air inside the barn. Here, fine high-pressure nozzles atomize and distribute water mist in the barn, generating evaporative cooling. This is a cost-effective and efficient way to reduce the temperature in the barn. However, when additionally cooling the pigs with water, care should be taken that the humidity in the barn does not increase too much. Above 20 to 25 °C, high humidity will otherwise cause the pigs to "feel" that it is even hotter than the thermometer would suggest. This is because in sweltering heat, evaporation of moisture through the skin and respiratory tract works less well, as the air is already largely saturated with water vapor. Controlling the temperature in combination with the humidity is therefore crucial for the cooling effect.