Risks associated with poultry production systems

Every poultry farm has its own risk profile for the introduction of pathogens, subsequent development of disease, and spread of pathogens to other farms. This risk profile is determined by a complex interaction between the levels of infection in an area, the measures implemented on the farm to prevent disease, and other factors including the density of farms in the area and linkages with other farms and markets. Farm biosecurity measures reduce, but do not eliminate, the risk of introduction or onward transmission of pathogens; they include factors such as the location of farms, the physical facilities, and the operational procedures implemented. Investments in these measures are subject to the law of diminishing returns. The Food and Agriculture Organization of the United Nations (FAO) has defined four production systems based partly on the biosecurity measures implemented. Distinguishing between farms on the basis of the measures practised is important, as not all intensive poultry production units apply biosecurity measures appropriate to the level of risk of virus incursion. Experiences with highly pathogenic avian influenza viruses of the H5N1 subtype have shown that farms in all production systems have experienced outbreaks, of highly pathogenic avian influenza, and that it is not possible to blame one particular system for the genesis or spread of the disease. Nevertheless, farms that rear ducks outdoors or where poultry are sold through poorly regulated live poultry markets appear to be high-risk enterprises, especially in countries where infection is present. Enhancement of biosecurity measures is generally agreed to be the best way to minimize this risk, but not all farms are in a position to implement stringent biosecurity, especially those that rely on rearing poultry outdoors. Formal risk analysis has rarely been applied to individual farms, but would assist in determining the benefits of existing and proposed on-farm biosecurity measures and in highlighting gaps in our knowledge regarding the levels of hazard for farms.