Rørvang, M. V., Blad, M., Lindahl, C. et al. 2024. An added aroma changes the behaviour of domestic pigs in a novel situation aimed for stunning. Applied Animal Behaviour Science 270, 106145.

The currently most widespread stunning method for pigs is high concentration of carbon dioxide (CO2), but this method is under scrutiny due to animal welfare deficits. One alternative method currently under development with potential to replace CO2 is nitrogen (N2) filled high expansion foam. While N2 does not elicit the same aversive behaviour as CO2, it is currently not known if the high expansion foam itself may be frightening to the pigs. Means to alleviate fear reactions to foam could consist of diverting pigs’ attention using aromas (an odour in combination with taste) of interest to them. The current study aimed to investigate if an added aroma (vanilla aroma) affected pigs’ avoidance and exploratory behaviour when exposed to air-filled high expansion foam in a foam box. The study included 50 pigs (30 females, 20 males) of 14–16 weeks of age, of different crosses between Yorkshire, Hampshire and Duroc. The pigs were randomly assigned to either the treatment with air-filled foam with added aroma or the control treatment with no added aroma, which they were exposed to in a foam box. The results showed that pigs with the aromatised foam expressed significantly more exploration behaviour directed towards the foam and box walls, but not towards the floor or the lid. The aromatised foam also resulted in a higher activity level of the pigs. In contrast to the hypotheses, pigs with aromatised foam expressed more avoidance behaviour, and escape attempts were exclusively observed when pigs were exposed to aromatised foam. Slipping events and frequency of vocalisations did not differ between pigs with and without aroma added to the foam. This study shows that an added aroma (taste and odour in combination) increased pigs’ exploration behaviour towards the foam, and thus could serve as a distraction for the pigs when inside a confined foam box. The results emphasise the importance of taking foam aroma into consideration in the further development of the N2-filled high expansion as a stunning method. The potential anxiety- or stress-reducing effect of any added aroma needs further investigation, and future studies should focus on assessing various types of aromas, and/or odours, as well as different concentrations of the compounds to determine which solution is most efficient in alleviating pig stress and anxiety.

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