The behaviours observed very seldom were startling, shaking, backing up and defecation. Because of how seldom these behaviours were seen it was not possible to analyse them further. It is however interesting that all these behaviours, which are thought to be related to stress or fear in pigs (Dalmau et al. 2009; Reimert et al. 2013), are observed in such small numbers. In an earlier study, startling is seen in 60% of the pigs (Lindahl et al. 2020), whereas in this study it is only seen in at most 15% of the pigs on day one in the repeated study.
Possibly as backing up was only observed on day one, it is an indication of fear that disappears on repeated days as the pigs get used to the sound from the foam generators and air pulse. But as it was only registered in a total of 8/50 individuals (16%) on the first day, that is a very weak indicator.
A behaviour that was noted, but not often observed on the videos, was defecation.
It was often seen before the start of the treatment, or in such places as were not seen from the cameras (the walls, or sides of the floor). There were many individuals that defecated at some time between being put in the box and taken out of it, even if few of these were caught on camera during the studied intervals. Defecation has been correlated to stress in pigs (Smulders et al. 2006), so that so many pigs defe-cate at some point during the trial seems reasonable. However, in future research it might be better to look at if the pig has defecated at all during the time in the box or not, and not count this in certain intervals or times only visible through the cameras. It would of course make it impossible to know if a certain part of the experience gives rise to a higher frequency of defecation, but it might still give more information about the experience as a whole.
49
Method consideration
The same person, the author, analysed all the video recordings and registered what behaviours occurred, which minimizes the risk of perceiving behaviours differently between pigs or treatments. A disadvantage with this approach was that it was not a blinded study and could therefore be a source of bias, but as the author did not have any stake or self-interest in the outcome of the study the risk was found acceptable. It was not always possible to see what the pig was doing with its’ head due to condensation on the lid, the box shifting position when the pig entered it or the head being on the edges of the box, which were not transparent. However, as the same person did all observations, and the conditions were similar in all trials, it should still be possible to compare the observations between treatments.
Considering the statistical analysis there is a risk of mass significance due to the number of statistical tests performed. However, the perceived relevance of the results is not only based on statistically significant differences, but also on the trends of observed behaviours. It would have been possible to further lower the risk of mass significance through advanced statistical analyses, but in this study there was no time for that.
The pigs used in this study were older, and therefore larger, than the ones used in previous studies, but the same test box was used. This most likely influenced the behaviours the pigs showed. Escape attempts via door or wall were not observed, and all escape attempts seen were interpreted as directed towards the lid of the box.
It is possible that escape attempts towards the top part of the door or wall, where the head and snout would be due to the size of the pigs, were interpreted as escape attempts towards the lid. In previous studies, escape attempts have usually been grouped together regardless of where they are directed (Lindahl et al. 2020;
Söderquist 2020; Thurehult 2019), as the motivator for the behaviour is likely the same and the main objective was to compare the frequency of escape attempts.
Another behaviour, which was not observed in the study, is lying down. This is most likely because the pigs were not relaxed enough to perform this behaviour. It was also noted that they did spend very little time, if any, lying down in the
“temporary pen” together with their pen mates as well. In total, it therefore seems likely that the pigs are simply not relaxed in the new section of the stable or in the foam box, which seems reasonable but still differs from one earlier study where lying down was seen (Lindahl et al. 2020).
There was a difference in how fast the box was filling up with foam, mostly having to do with how the pigs were standing and how much they were moving. This affected how much time each pig spent completely covered by foam, and also when
50
the air pulse destroying the foam was started. As the air pulse destroying the foam made a different noise and occurred in different intervals for different pigs it is possible that behaviours showed in the latter intervals are affected by this.
In choosing what scent that was to be added to the foam solution in the treatment
“scent” consideration was taken into account of what type of scent was thought to induce as little irritation in the face of the pig. Vanilla aroma approved for human consumption was then decided to be the kindest alternative possible at this time. As far as deciding on a concentration, vanilla aroma was added to the foam solution until the vanilla scent could be detected and the chemical “scent” of the foam solution was less strong. For future research it would be interesting to try different scents and concentrations and carry out studies where pigs would choose from these.
Lastly, the floor of the box has to be transparent to be able to study behaviour, but this also makes the floor slippery without application of anti-slip tape. However, as the tape wears off over time, the floor gets more slippery day by day. Thus, it is necessary to re-apply tape after a certain number of pigs, depending on how much the pigs are moving around, but still, that is a factor that will differ between days which could have influence on pig behaviour.
Conclusion
When the foam had an added scent, the pigs showed significantly more exploratory behaviour indicating an increased interest to the foam throughout the whole trial.
Therefore, it can be concluded that adding a scent to the foam solution may be a way to distract the pigs and possibly to make the experience less uncomfortable for the pigs. There was an increase in the number of escape attempts in treatment
“scent”, but as this was in very small numbers it is harder to evaluate and makes the results less clear overall. Adding a scent to foam would need further research on other types of scent and concentration to determine the best scent to be added and to make sure that it does not affect the end product e.g., quality or food safety aspects. It also needs further research to ensure that the change in behaviour seen is actually correlated to a lower level of stress.
When the pigs were repeatedly exposed to foam, exploration of the wall and vocalisations became more frequent with exposure occasions. Their behaviours did not indicate that pigs got a very increased fear or stress reaction when repeatedly exposed to foam, but neither did their stress related behaviours decrease. The most clearly stress-related behaviour such as escape attempts and avoiding of foam was seen in too low numbers to draw many conclusions from. An increase in
vocalisa-51
tion overall could also have different explanations, from anticipation of soon being let out, to increased anxiety. This is why further studies would be needed to evaluate the levels of anxiety in this situation. A larger number of pigs on an increased number of days would probably yield more conclusive results.
52
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56
First, a big thanks to Anna and Cecilia especially for all early morning meetings and for answering my stressed phone calls from Lövsta. Thank you also to Emma, who helped me with the pigs, and to the staff at Lövsta for making room for us there. Thanks to Moa, without whom I would not have gotten through the last few years, and to Simon, for supporting me endlessly.
Acknowledgements
57
Alla djur som slaktas i Sverige måste bedövas innan avblodning, och beroende på djurslag finns olika metoder tillgängliga. För gris är de vanligaste bedövnings-metoderna koldioxid och elektricitet. Vid elektrisk bedövning placeras två elektroder på vardera sida av grisens huvud och en stark ström leds igenom vilket orsakar ett epilepsilikt anfall som leder till medvetslöshet. Den största nackdelen med denna metod är att grisarna behöver drivas en och en fram till bedövningen, vilket är problematiskt då grisar är sociala djur som föredrar att röra sig i flock. Det krävs också någon form av fasthållning av grisarna för att elektroderna ska kunna placeras korrekt, vilket också bidrar till mycket stress för grisarna och för personalen som hanterar dem. Vid bedövning med koldioxid sänks grisarna gruppvis ner i ett schakt med ökande koldioxidkoncentrationer, vilket efter en period på upp till 30 sekunder ger en sänkning av pH-värdet i centrala nervsystemet vilket ger upphov till medvetslöshet. Den största nackdelen med denna metod är att grisarna uppvisar kraftigt obehag när de sänks ner i koldioxiden, de flämtar efter luft, skriker och försöker fly. I studier på människa har exponering för höga kon-centrationer koldioxid gett upphov till starka reaktioner av rädsla och oro. Redan år 2004 fastslog av EFSA (European Food Safety Authority) att båda dessa metoder har omfattande brister ur djurvälfärdssynpunkt, och att nya studier inom ämnet behövs för att hitta alternativ – men trots detta har endast ett fåtal nya studier publi-cerats inom ämnet sedan dess.
En viktig del av utvecklandet av nya bedövningsmetoder är att utgå ifrån djurens normala beteenden. Grisar är som tidigare nämnts sociala djur som vill röra sig i grupp, varför metoder som underlättar drivning och bedövning i grupp är att föredra för att minska stress för både människor och djur på slakteriet. Den typ av nya metoder som främst undersöks i dagsläget är därför bedövning med gas av olika slag, eftersom det möjliggör just gruppbedövning. I EU är inerta gaser så som argon, helium och kvävgas redan godkända för bedövning av gris. Dock finns det inte några alternativa kommersiella bedövningssystem tillgängliga, detta på grund av begränsade studier inom ämnet samt både tekniska och ekonomiska utmaningar kvar att lösa. Både argon och helium anses vara för dyra för att fungera i stor skala, men kvävgas är billigt, lättillgängligt och inerta gaser har i studier inte visat sig ge upphov till samma kraftiga obehag hos grisar som koldioxid. Vid användning av