Does feeling good prevent us from sensing danger?

For sheep, smell is a real guide. From birth, lambs identify their mothers by their smell. Later, they will distinguish their fellow sheep within the flock or recognise safe food to eat. Certain smells, such as orange, can even make food more appetising. Conversely, the smells of predators (dogs, wolves, etc.) are repulsive.

The researchers wanted to see if these smells had the same effects (fear, attraction, disgust) in a “positive” context, limiting stress, characterised by the presence of other ewes and access to food.

Thirty adult Ile-de-France sheep with identical life histories were tested individually in a corridor where they could both see other sheep and access food (pellets). Three odours were presented on a cotton pad placed in a transparent box also containing food:

• Orange essential oil, assumed to be pleasant;
• Wolf droppings, supposed to cause fear;
• Cadaverine, a molecule characteristic of decomposing bodies, supposed to cause disgust.

The order in which the animals were tested was determined after a familiarisation phase, in order to avoid any stress related to handling. The animals were tested in the same order in each experiment, taking into account their catchability and/or personality.

Each ewe was filmed for five minutes in order to analyse its behaviour: time spent eating, proximity to other animals, exploration of the box containing the odour, number of vocalisations, etc.

The behaviour of the ewes was not always as expected:

1. The smell of orange, neither particularly appealing nor repulsive.

Contrary to expectations, orange essential oil did not trigger any particular behaviour. The sheep ate normally, showing no particular interest in the source of the smell. Researchers believe that other positive elements in the environment (available food and the presence of other sheep) may have masked the appetising effect of the orange scent.

2. Wolf droppings, discreetly repellent.

The smell of wolf did have a negative effect, but it was moderate. The sheep spent less time near the food and ate less. However, they did not show clear signs of stress or fear: little vocalisation, no flight or agitation. Their attention simply seemed to be diminished.

3. Cadaverine, a surprise.

This molecule associated with death caused neither fear nor avoidance. Only two sheep had gagging reactions, a possible sign of disgust. The others ate normally.

A balance between pleasure and caution

The results suggest that sheep constantly weigh up pleasure and caution. As with humans, animal emotions depend on context and personality: some sheep were very attracted to food, others more to the social group.

In all cases, the presence of appetising food and soothing conspecifics seems to reduce attention to ‘threatening’ odours.

Results that raise questions about the use of odours in livestock farming

A better understanding of how odours influence the behaviour of farm animals could help improve their welfare. For example, certain odours could be diffused to reduce stress during shearing or transport. However, this study shows that reactions to odours are subtle and depend on other environmental factors: a pleasant odour will not necessarily have an impact if the animal is already relaxed.

This study highlights the complex interaction between social, dietary and environmental factors in triggering emotions in sheep through olfactory stimuli, emphasising the importance of context and individual variability. It calls for caution in the use of odours to induce positive emotions (or avoid negative emotions) and suggests that social and dietary resources may be more effective levers for reducing stress in the face of risks such as predation. A specific study separating the effect of food from that of conspecifics would validate the hypothesis suggested by this work.