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Introduction
A good air quality is required for maintaining animal health and welfare and for providing a good working environment for the staff. Air quality is characterized by the content of gasses, dust and micro-organisms (bacteria, endotoxins and vira) in the ambient air of the pig building.
The pigs’ respiratory and integumentary systems are directly exposed to the air and therefore also to air pollutants, which might exert both direct and indirect effects. Skin, eyes and the mucosa of the respiratory tract are directly affected and irritated by pollutants, which might facilitate the indirect effects of diseases.
Gases
The air contains numerous gases. However, the most prominent ones are those released from animal waste including ammonia (NH3), carbon dioxide (CO2), carbon monoxide (CO) and hydrogen sulphide (H2S). Along with these a number of odourous compounds such as amines, organic acids, amides, alcohols, carbonyls, skatols, sulfides and mercaptans are present. During the last decade air pollution research has been focusing increasingly on the latter ones because many of these compounds are believed to be the most important sources of odour from animal accommodations. An international working group “CIGR” has evaluated effects of noxious gases and made a set of recommendations regarding maximum concentrations (Table 1).
Table 1. Maximum concentration of gases in animal accommodations (CIGR-norm – international recommendation measured as volume concentration)
| Gas | Concentration, ppm |
| Ammonia (NH3) | 20 |
| Carbon dioxide (CO2) | 3000 |
| Carbon monoxide (CO) | 10 |
| Hydrogen sulphide (H2S) | 0,5 |
Ammonia is a toxic gas, which is generated and released when urine and faeces are mixed. Ammonia has a lower density than atmospheric air and is therefore present in the pig building. Pen design, straw application and choice of waste handling system affect ammonia concentration. Generally, ammonia concentration is low when pen floors are clean and waste surface area is small. Thus, a solid floor, which is fouled with feces as well as a fully slatted floor will result in a high ammonia concentration.
American studies have shown that ammonia concentrations of 50 ppm and 100 ppm reduced daily weight gain of young pigs with 12% and 30%, respectively, while reducing their ability to clear bacteria from their lungs.
Ammonia release to the surrounding air has become one of the hottest issues with respect to obtaining permissions for expansion of pig units in many EU-countries – especially for animal units located close to environmental protection zones. Thus, several thousand tonnes of ammonia are produced from animal accommodations each year and EU’s IPPC-Directive (Integrated Pollution Prevention Control) states that measures must be taken to reduce pollution with ammonia among other things. Therefore, partly slotted floors and air cleaning technology are applied more and more often in new pig accommodations.
Carbon dioxide is produced in large quantities from the pigs’ lungs and arises from metabolism of nutrients. The concentration of CO2 varies with stocking density, feeding regimen and animal activity and it might be used as an indicator of ventilation efficiency. Thus, some ventilation manufacturers have started using CO2 sensors as part of their control system. A high CO2 concentration is an indicator of poor ventilation. Under normal ventilation conditions carbon dioxide concentration is maintained below 3000 ppm even during winter conditions if the ventilation system is maintaining the relative humidity below 70%.
Carbon monoxide is a toxic gas generated from incomplete combustion of gasoline in engines. However, in pig production this gas does not constitute a problem.
Hydrogen sulphide is a toxic gas, which is more responsible for deaths in animal housing than any other gas. This gas is formed continually during anaerobic decomposition of excreta. It is denser than air and smell like rotten eggs at low concentrations (< 50 ppm). At higher concentrations it is odourless. The ventilation system might not be sufficiently efficient in discharging the hydrogen sulphide due to the fact that the gas is heavier than the ambient air. When waste is agitated or discharged from pits hydrogen sulphide is rapidly released and might reach concentrations of 50 ppm or more. The greatest risk of high gas concentration is associated with deep pits and recycling waste. Since it cannot be smelled at the higher concentrations the staff might conclude that the danger is over. In the worst case both animals and persons become on-conscious and die within a relatively short time after exposure to high concentrations (Table 2).
Table 2. Human reaction to Hydrogen sulphide
| Concentration of Hydrogen sulphide, ppm | Human reaction |
| 0,025-0,1 | Detection of smell |
| 1 | Weak smell |
| 3-5 | Aversive smell |
| 10 | Hygienic maximum concentration for one working day |
| 30 | Very strong aversive smell |
| 50-100 | Reduced sight and difficulties with breathing |
| 100-200 | Coughing and difficulties with swallowing Sense of smell inhibited after 2-15 minutes Dizziness after 15-30 minutes |
| 350-450 | On-consciousness and death after 1 hr exposure |
| 500-600 | On-consciousness and death after 0.5 hr exposure |
| 600-700 | On-consciousness and death after 2-15 minutes exposure |
| 700-2000 | On-consciousness and death after 1 minute exposure |
Dust
Dust is produced from animals’ skin, hair, straw, feces and feed and comprises particles that are airborne. It also contains vira, bacteria, endotoxins and fungi. Dust concentration is depending on animal activity and during the daytime concentration levels are double of those during night. Dust particles serve as an important vector for transmission of infections. Via the ventilation air large quantities of dust particles and bacteria/vira are exhausted from pig buildings.
Dust particles are divided into inspirable (total dust including respirable dust) and respirable (< 5 µ) dust. Most dust is removed from the pig buildings via the ventilation system. However, dust levels do vary with housing system as shown in Table 3. Furthermore, it might be reduced by improved management of feed, e.g., use of lids on feeders, use of vacuum cleaners and addition of fat and oil in the pig diet. Application of dust binding technology, which includes oil-spraying systems have been very efficient in reducing respiratory dust levels and protecting animal workers from health problems. In addition, filters (P2-type) and air cleaning helmets might be useful.
Table 3. Dust concentration associated with housing
| Highest dust level | Lowest dust level | Dust reduction potential | |
| Feeding system | Dry | Liquid | 20-25% |
| Straw | With straw | Without straw | 20-25% |
| Ventilation | Neutral pressure Positive pressure |
Natural ventilation Negative pressure |
15-20% |
