Friend or foam? Improved methods for stunning of pigs with foam : effects of repetition and scent on pig reaction to foam

Sammanfattning: There are several methods available for stunning of pigs before slaughter, but the most frequently used at larger abattoirs are electricity and CO2. There are advantages and disadvantages with both methods. As there is no method that does not have major animal welfare drawbacks. EFSA (European Food Safety Authority) concluded in 2004 that research on new and developed methods for stunning of pigs before slaughter needs to be prioritised. However, research in the area is lacking. One method that has been researched is stunning with nitrogen filled high expansion foam. With this method it is possible to use a gas (e.g., nitrogen) that is not thought to be as aversive to pigs as carbon dioxide, but that is difficult to use in free form due to having similar density as air. The foam keeps the gas from mixing with air and purges the space from air helping to create an anoxic environment in a shorter time. When this method has been studied, questions have arisen on how aversive the foam itself is to the pigs, and whether or not it is possible to reduce this aversiveness by, for example, adding a scent to the foam or by exposing the pigs to foam on repeated occasions. The aims of this study were to investigate if the pigs’ behaviour were altered when scent was added to the foam, and also if repeated exposure to foam would affect the pigs’ behaviour. In total, 50 pigs with an age of 14-16 weeks were included in this study. There were 30 pigs in the group with a vanilla scent added to the air-filled foam, and 20 pigs in the group that was exposed to air-filled foam without an added scent on three consecutive days. The observations from the first exposure to foam in the group with 20 pigs in the repeated study were also used as a control group to the study with an added scent. The result from the experiment with foam with an added scent showed that there was a larger proportion of pigs exploring the foam when it had an added vanilla scent. There was also an increased interest in that group to explore the wall, as well as increased activity. No effects could be shown on number of escape attempts. The result from the experiment where pigs were exposed to foam on three consecutive days showed a larger proportion of pigs vocalising, both in forms of grunts and screams/squeals, on day three than on day one. There were also more escape attempts on day three than on day one. Furthermore, increased exploration of the walls and decreased exploration of the floor was seen from day one to three. In conclusion the results of this study indicate that it is possible to increase the pigs’ interest in the foam by adding a scent to the foam. If foam is to be given an added scent in the future more research is needed, both in terms of relevant scent and concentration as well as assuring it has no effect on the meat for the consumer. The results also indicate that the foam is not highly aversive to pigs, as pig avoidance behaviour towards the foam does not greatly increase when exposed to it repeatedly. Number of escape attempts increased slightly however, and a future study with a larger number of pigs might reveal more information. The increased vocalisation could either indicate a return to more normal levels of vocalisations because of adaption to the environment but could also mean an increased reactivity to the situation. It is also possible that increased vocalisation comes from knowing that that they will soon be let out and therefore try to communicate with their box mates. Further studies would be needed to confirm stress levels in the pigs in these situations.