The risk of Avian Influenza on cultivated free range poultry farms

Abstract

The Netherlands is an important producer of eggs and egg products. Outbreaks of Avian Influenza (AI), especially when a high pathogenic virus is detected, can result in massive destruction of poultry and large economic losses. Free range poultry farms have a 11 fold chance of getting an AI infection, compared to poultry farms without an outdoor area. In the light of an ongoing project, which aims to attract more poultry to the outdoor area through the planting of biomass crop (willow and miscanthus) or fruit trees, it was questioned to what extent this vegetation would attract (extra) wild birds and whether this would increase the risk of AI virus infection compared to poultry farms with an outdoor area (free range poultry farms). This literature study aimed to find an answer to this question. From large scale studies, in which thousands of wild birds belonging to many bird species were tested for AI viruses, a list of risk species was made by Veen et al. (2007). This list included several bird species (mostly water birds or shore birds) that were classified as high risk species (HRS), due to the prevalence of HPAI H5N1 (a highly virulent virus subtype) detected in individuals of these species. Selection of the other risk species was mainly based on their potential to act as bridge species between these water birds and poultry farms; their gregariousness; colonial breeding; predatory and/or scavenging behaviour. Former studies on bird abundance at willow coppice; orchards and mis-canthus were reviewed, specifically with regard to the birds listed as risk species. Comparison with the bird abundance found on or near free range poultry farms showed that most of the HRS seen on or near these poultry farms were absent at the miscanthus and willow plantations. In addition, willow coppice and miscanthus held distinctively less other risk species compared to free range poultry farms. The amount of HRS and other risk species at orchards varied depending on the presence of ditches and windbreaks. It was suggested that region; surrounding environment; design of the plantation and other management factors (such as weed control) might also have contributed to differences in bird density and/or species diversity between willow coppice and miscanthus studies. In addition, there was indication that the presence of a poultry farm might influence the species diversity of the surrounding fields. From the results of the comparative analyses, it was concluded that there was a strong indication that cultivation of the outside enclosure on free range poultry farms with willow coppice; orchards or miscanthus might decrease the risk of AI infection. It was further estimated that the overall risk of initial AI infection would be very low and fairly equal for all three vegetation types, with miscanthus estimated as having the lowest risk and orchards as having the highest risk of all three vegetation types. However, it was emphasized that this risk can be highly influenced by co-factors, such as the presence of open patches; wind breaks; water bird areas and weediness. Based on the risk analyses and the fast growing character of miscanthus, and hence their supposedly quick impact on the bird abundance of the plantation, it was indicated that miscanthus might be the best plant species of all three vegetation types.