Air quality in pig buildings

A base level of ‘fresh air’ ventilation is required in all livestock buildings to help maintain animal and stockperson health and performance. Use this information to understand more about major pollutants.

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Why is air quality important?

There are a number of major pollutants that must be limited to help maintain the health of your pigs, since some can be detrimental to animal health and productivity.

It is also important to limit pollutants for the health of stockpersons, too. The information below covers the major pollutants.

Carbon dioxide

Farm animals, in common with humans, expel carbon dioxide (CO2) from their lungs and high concentrations are known to negatively affect performance.

CO2 levels are often cited as being the factor which limits how low ventilation rates can be taken and a value of 0.3 per cent has been used to determine the minimum ventilation rate recommended for pigs.


Ammonia (NH3) is given off by the excreta of animals and can be a problem.

The concentrations of ammonia are generally higher in deep-pit slurry systems, with slats and mechanical ventilation, than in other types of pig housing.

International agreements on air pollution have resulted in the UK farming industry being required to achieve a 16% reduction in ammonia emissions by 2030.

Ammonia emissions factors trials

Hydrogen sulphide

Hydrogen sulphide (H2S) is also a by-product of excreta. This poisonous gas can build up to dangerous levels in stagnant or poorly ventilated areas. 

As with ammonia, it prevails in deep-pit slurry systems with slats and mechanical ventilation.

Water vapour is not in itself poisonous, but extremes of humidity are thought to be detrimental to animal health. High relative humidity can also lead to problems with condensation.

Carbon monoxide 

Carbon monoxide is produced when fossil fuels, such as liquid petroleum gas (LPG) or oil, are directly burned for heating. The output of the gas can be excessive with badly-maintained heaters where fuel is not being burnt completely.

High levels of carbon monoxide have been linked to an increased incidence of stillborn piglets. Monitoring is recommended as a safety precaution.

With indirect fossil fuel heating, products of combustion are vented through a flue and no products of combustion enter the building air space. As well as producing carbon monoxide, direct-acting fossil fuel heaters add to the levels of water vapour and CO2, which must also be vented.

Particulate matter

Fine dust or particles can cause issues for the lung health of both pigs and stockpeople. Various solutions are available that allow reduction of particulate matter including: