Smells like welfare - the use of odours to lower fear and stress in cattle and horses

Olfaction is the primary sensory modality for most mammalian species including our farm animals (Nielsen et al., 2015). This means that their olfactory environment is of great importance for their wellbeing. Odours may thus represents untouched potential for future tools to safeguard animal welfare (Wells 2009; Nielsen et al., 2019). From rodent studies we know that rats can learn to associate an unrelated odour, with a pleasant interaction with a human (tickling) (Bombail et al., 2020), and male rats prefer to mate with females that smell of almond (or even cadaverine) if they have previously copulated with females doused with these odours (Kippin and Pfaus 2001; Pfaus et al. 2001). There is thus reason to argue that farm animals might also be able to form a positive association between odours and a pleasant experience. Such association could be useful in several situations, e.g. to attract animals to a certain place (i.e. to limit the need for physical moving the animals, which is often associated with high risk on injuries and stress, e.g. Lindahl et al., 2016; Simon et al., 2016). Another efficient means to alleviate stress and anxiety from the human world is the so-called scent-scape (Pálsdóttir et al., 2021). In the scent- or smell-scape an odour (e.g. a conditioned odour (as described above)) is used to alleviate imminent anxiety or fear. This method is used in cognitive behaviour therapy and in urban restorative mental health settings (Hedblom et al., 2019). Although the mechanism is not fully understood, the odour might be a way of diverting attention from the negative emotions and promoting positive emotions. The odour used for this purpose is often essential (i.e. natural) oils. As in humans, some of these odours appear to encourage relaxation and alleviate stress in animals. The ambient odour of lavender, for instance, has repeatedly been shown to decrease motility in laboratory-housed rodents (Buchbauer et al., 1991; Lim et al., 2005; Shaw et al., 2007). The same herb has been shown to reduce activity and vocalisations in dogs housed in rescue shelters (Graham et al., 2005). Odours might thus be useful in on-farm situations both to optimise management routines in the daily procedures, but also during procedures normally associated with high stress. Such situations could e.g. be during transportation, or during veterinary treatments. Odours may in these situations ensure a safer and calmer environment for both humans and animals involved. These mechanisms are the focus of the current phd project, which will investigate several aspects of using odours in on-farm situations as means to alleviate fear and stress in two species: horses and cattle. The PhD project combines the scientific disciplines of neuroscience, ethology and cognition, and includes four studies.

To study the above objective the project is divided in two parts:

1. Olfactory conditioning and proof of concept – answering the question: can horses and cattle be trained to associate an odour with a pleasant situation?
2. Lowering fear by use of odours – answering the question: May the positive odour conditioning established in part 1 be used to lower stress and fear reactions in horses and cattle during a stressful event?