Pig housing: Avoiding heat stress

The warm temperatures this year are stirring memories of 2018’s sizzling summer. Back then, long periods of high temperatures often led to heat stressed pigs. But even in »normal« summers, overheating can be a problem. And not only in southern European countries.

Even at 25°C, nursing sows react with reduced feed intake. From 80 kg liveweight, feeding pigs can suffer from blood circulation problems. Pigs can’t sweat. They are only able to lose surplus body heat and residual metabolic energy either through increasing respiration rate or by direct heat loss via the skin (cool lying surfaces).

Cooling pig housing when it is extremely hot outdoors is a legal requirement. For instance, Germany’s Animal Welfare Act (Farm Livestock) stipulates »a suitable method must be available for reducing any heat stress suffered by pigs through high temperatures in their accommodation«. There’s also the powerful argument that a comfortable housing climate helps the animals achieve performance potential.

Where there’s no satisfactory way of keeping cool, pigs reduce feed intake because this cuts back on heat produced by metabolic activities such as digestion and milk production. In particular, nursing sows start using more of their body reserves, increasing transformation of fat which, in turn, may reduce breeding performance.  As well as performance penalties, heat stress increases the possibility of pig behavioural disorders, e.g. tail biting and aggression.

Before technical measures are applied, consider the existing buildings and equipment. With a correctly adjusted ventilation system a cooling effect can be achieved through increased air speeds (with air temperatures over 30°C). Planting bushes/trees around the building and/or increasing eave overhang can stop direct sunlight through windows, offering effective reduction in heat stress. In general, planting shrubs/trees also avoids heat building-up in the walls of pig housing.

»For best possible cooling effect, the location of the fresh air intake plays an important role«, says Bernhard Feller, an advisor with North-Rhine Westphalia Chamber of Agriculture. Air intake should preferably be in shadowed locations on the north or east aspects of buildings. Here, intake air temperatures during the critical summer months can be 2 – 3°C lower. Also more effective is siting air intake through adjoining open buildings. A particularly bad idea, on the other hand, is taking intake air from uninsulated below-roof space of pig housing.

Pig accommodation can be cooled indirectly through spraying water on the roof surface, e.g. via garden sprinkler systems. This reduces heat build-up in the building materials. Such action can reduce temperature of ventilation air drawn from ceiling spaces by 3 -5°C. With roof sprinkling, it’s important that as little water as possible flows off the roof. From ridge to eave, the aim must be highest evaporation rate for optimum cooling effect. Photovoltaic panels on the roof help protect the building from heating up.

Direct cooling in pig housing is possible through a built-in geothermal heat exchanger: very expensive but effective. Hereby the inlet air is drawn through pipes buried under, or alongside, the pig housing. A great advantage of this system is that cooling occurs without air moisture content being increased, so the system is not dependent on ambient air humidity.

Less expensive, and available for retrofitting, are air humidifying systems. With spray cooling, a mist of water droplets is formed through high-pressure or low-pressure misting nozzles. The suspended droplets cool the ventilation intake air through their evaporation. But high air humidity limits the efficacy of this approach – although fine »haymaking weather« is ideal for such systems.

Low-pressure misting has the advantage that they can be based on existing pig house soaking equipment and so reduce investment requirement. A cooling capacity of 4 – 5°C can be expected in such cases, although relatively large droplets limit efficiency. »This type of cooling should no longer be applied where relative humidity is above 70 – 80 %«, cautions Bernhard Feller.

With a high-pressure system, a cooling effect of 6 – 8°C is achievable. The droplets produced are then much finer, working well at 80 % relative humidity. However, the costs and the maintenance requirements of the necessary plant are very much higher than those for low-pressure systems. High-pressure systems have other advantages: they can effectively bind dust and moisturise heating air in winter. Not only can spray cooling be directly applied in respective compartments, it can also be installed near air intake points. Bernhard Feller advises that an especially fine moisture suspension needs to be produced for best possible air uptake. One thing to definitely avoid is condensation or droplet precipitation forming in air canals or in any pre-ventilation air holding spaces.