Tuesday, 27 March 2012

How can you tell your sheep is happy?

Have you ever wondered how you can tell how your sheep feels? Observing the emotions of sheep can be really difficult because sheep tend not to express a lot of emotions. This is probably advantageous for the sheep because they are prey animals, and giving away that they are scared, in pain or sick could make them an easy target for predators. However, the fact that they don’t show many signs of emotions doesn’t mean that they do not experience them, although it can be very difficult for their owners to get insight into their emotional state.
Humans generally express their emotions by body postures and facial expressions (among other means).  For example, a smile generally means that someone is happy (positive state) while a frown may indicate that someone is angry (negative state). Other mammalian animals also use facial expressions of emotions; monkeys and rats can express both pleasure and disgust. Such facial expressions are also very important in communicating emotions to others and play an important role in social relationships.  However, sheep do not have a good superficial facial muscle network and this limits their ability to show facial expressions of emotions.  Recently, researchers have started to investigate other potential ways of emotional expression in sheep and they have started to look at the position of the ears. Most sheep owners would have noticed that sheep generally move their ears a lot and point their ears towards an object/event when they are paying attention to it.
The researchers placed sheep in several different situations (negative and positive) and observed their ear postures. They identified the following main ear postures:

Forward ear posture
Forward ear posture
The forward ear posture (sometimes the ears are also raised) has been observed when sheep are exposed to an unfamiliar situation (the appearance of a scarf that the sheep had never seen before). This posture has also been observed when sheep were separated from their flock members, which is very stressful for sheep.

The forward ear posture could be a sign of increased attention when placed in a novel situation (or when looking at a strange camera), or it could be a sign of distress.

Neutral to backward ear posture
Backward ear posture
Sheep generally have their ears neutral (perpendicular to the head-rump axis) or backward when they are standing calm and quietly, for example when ruminating. The proportion of time spent with their ears in the backward position increases even further during positive situations such as feeding and being voluntarily groomed by their handler.
The neutral-backward posture therefore seems to be an indication of a calm state, and perhaps even of positive emotions. However, in a different study the backward ear posture was also observed during a situation when sheep could not control a grid moving over their feeding troughs that prevented them from eating. Sheep that were taught to remove the grid by crossing a photo beam with their muzzle did not show the backward ear posture as frequently.

Asymmetrical ear posture
Asymmetrical ear posture


The asymmetrical posture (one ear pointing back and the other ear pointing forward) has often been observed when sheep are distressed in situations such as separation from group members. The asymmetrical posture may also be an indication of frustration; sheep showed this posture more frequently when they were given a smaller food reward then expected.

Number of ear posture changes
It has also been observed that sheep will change ear postures very frequently when they are stressed, while the ear postures change less often when in a more positive state such as feeding or ruminating. Sheep that constantly change their ear postures may therefore be in a negative state.

I have observed that the specific postures tend to differ between breeds. For example, the Coopworth x Texel crosses shown in the pictures can raise their ears, but merino sheep do not appear to be able to raise their ears too much. Merino sheep seem to move their ears more along the horizontal plane than the vertical plane. I have also noticed that merinos do not show the neutral ear posture (ears perpendicular to the head-rump axis) or the passive ear posture (ears hanging down passively and dangling along with head movements) frequently, in contrast to some other breeds. So keep in mind that there may be some breed differences when you observe your own sheep’s’ ear postures.
I also believe that the ear postures may be context dependant. For example, the backward posture has been observed in both negative and positive situations, although there may be subtle differences that have not been captured yet. Some of my colleagues have also observed the backward ear posture when (merino) sheep are in pain (for example after museling or castration without pain relief) and this posture is often combined with a hunched back and behavioural apathy. So please bear the context in mind before you interpret the backward ear posture of a sheep in pain as a sign of positive emotions!

References
Boissy, A., A. Aubert, et al. (2011). "Cognitive sciences to relate ear postures to emotions in sheep." Animal Welfare 20(1): 47-56.

Reefmann, N., F. B. Kaszas, et al. (2009). "Ear and tail postures    as indicators of emotional valence in sheep." Applied Animal Behaviour Science 118(3-4): 199-207.

Reefmann, N., B. Wechsler, et al. (2009). "Behavioural and physiological assessment of positive and negative emotion in sheep." Animal Behaviour 78(3): 651-659.


1 comment:

  1. Else,
    Thanks for the article. I have noticed our ram has a very distinctive display of his lips. He draws his lips apart to show his closed teeth. I think this is apparent when he is near a ewe he likes. I have not made a photo, are you interested to see his facial expression?
    Chris ann_chris@bigpond.com

    ReplyDelete