Acceptable methods for large scale on-farm killing of poultry for disease control

Abstract

Abstract Worldwide large numbers of birds are killed to stop the spreading of contagious diseases like Highly Pathogenic Avian Influenza (HPAI). From animal welfare and epidemiological point of view animals are preferably killed on the premises and if possible in their housings. Furthermore, applied methods should be effective, have large capacity and animals should be unable to escape from it. In this thesis, animal welfare aspects, i.e. behavioural and physiological, and efficacy aspects of gas killing were assed for individual birds and groups of poultry. Observations during the 2003 HPAI outbreak in The Netherlands made it clear that whole house gassing with carbon dioxide is a method with high capacity and is relatively safe. Also, birds don’t have to be handled and transported to a killing device which is a major advantage for their welfare. Questions that raised about the suitability of carbon dioxide to kill ducks and turkeys were answered in experiments where ducks and turkeys were exposed to increasing carbon dioxide concentrations. In these experiments blood gas values, EEG’s and ECG’s confirmed that both species are equally sensitive to these increasing carbon dioxide concentrations. Furthermore, the results found in ducks and turkeys are comparable with results found in chickens and confirmed that all farmed poultry species can be killed by increasing the carbon dioxide concentration up to 40-45%. However, it is unmistakaeble that killing animals always interferes with their welfare. Before loss of consciousness all animals express heavy breathing (gasping) and headshaking during a period of 2 to 3 minutes. Convulsions, if they occur, are seen after loss of consciousness. Therefore, it can be concluded that the period of compromised animal welfare is not longer than 3 minutes. This period of compromised animal welfare however, is shorter than when animals are caught and handled when using mobile gas containers or mobile electrocution lines. Large scale killing of animals for disease control purpose meets a lot of societal resistance, especially when alternatives like vaccination are available. Furthermore, the visibility of the depopulation of poultry farms makes people aware that large numbers of birds are killed in our society every year. The moral attitude of people towards killing animals is strongly coloured by the reason why we kill animals; killing for food is more accepted than for disease control. However, we should realize that animal welfare is presumably more compromised in the normal slaughter process than when killed in their housings for disease control. Also, it is not realized that the non vaccination policy is an economical policy to protect our export position, something that benefits producers and consumers. In respect of animal welfare and of the moral attitude of man the non- vaccination policy should be reconsidered. However, we must realize that there will always remain situations that farms must be depopulated and therefore we should provide maximum effort in further developing acceptable killing methods.