Hygiene and air quality in intensive housing facilities in Australia

Abstract

The standard of air and surface hygiene in intensive animal houses has a significant effect on animal health and production efficiency, as well as influencing the respiratory health of employees. Over the past decade, sub-optimal air quality and surface hygiene have been associated with increased prevalence and severity of enteric and respiratory disease in animals, as well as reduced growth rate. The key pollutants include gases such as ammonia, carbon dioxide and hydrogen sulphide, and airborne particles and bioaerosols, consisting of a range of material from organic and inorganic sources. These include minerals and ash, undigested feed, cellular components of gut epithelium, grain mites, dried dung, skin and feather dander, as well as a collection of micro-organisms and their cellular components and metabolic products. The major source of the gases and bioaerosols is the animals and their effluent. While the effect of the pollutants on animals is not fully understood, it has been demonstrated that a number of pollutants are capable of initiating an inflammatory response in tissues of the respiratory system. Various combinations also appear to be capable of triggering immune responses and physiological changes in animals that result in reduced feed intake and depressed growth rates. It is also hypothesised that protein and energy are diverted from the development of muscle to maintain the immune response. The key to improving air quality and surface hygiene is to eliminate pollutants at their source, or reduce their production. The important factors that have a negative influence on air and surface hygiene include the farming system practiced, the species farmed, and the size and behaviour of the animals housed. Other factors include building characteristics, the shed environment, and husbandry. The characteristics of the building that influence hygiene and air quality include the shape and dimensions of the building, the ventilation and heating system used and effluent management. Shed environmentalfactors include the level of cleaning and disinfection, the state of the pen floors, and watering and feeding systems, as well as the quality of water used for cleaning and effluent removal. Husbandry factors include stocking rate and density and shed population size.