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Emotional reactivity and laterality in sheep

In 2013/2014 I worked on a project investigating different aspects of sheep behaviour. Cute little animals they are...but so nervy! Highly reactive and fearful animals, especially production animals, can be a serious problem for the stockman (because of difficulties in handling them), for the animals themselves who are experiencing high stress levels, and for the farmer, as high reactivity has been associated with loss in production rates. Thus, it is very important to find predictive indicators of fear and behavioural reactivity in sheep to improve management systems and animal welfare overall.

As fear has been shown to be a consistent trait in time and across different situations, in a first study we searched for predictive measures of fear by correlating measures of behavioural reactivity across two different tests: an isolation test and a mother-lamb partial separation test, both known to elicit mild fear and stress response in sheep. Results showed that there was an effect of breed: amongst ewes, Dorset were characterised by a more calm temperament while Sarda (especially primiparous ewes) were more active in their response to challenge (i.e. more attempts to escape). Overall during isolation lamb fear score was on average significantly higher than dams. We also found a positive correlation between vocalisation to locomotor activity, meaning that more stressed animals would pace more in the arena and vocalise more than calmer animals. To learn more about these results, read here Barnard et al. 2015 App Anim Behaviour Sci.

This punk-looking ewe in the picture is ready to be released in the test area where she will have to decide whether to avoid a central obstacle by going left or right, to re-join to a flock mate on the other side. Why, you ask? because this way I could assess sheep motor laterality, the second proxy measure of behavioural reactivity investigated in a second study within this same project.

Photo credits Shanis Barnard

Correct, because behavioural laterality in emotional situations (such as being separated from the flock) reflects the divergent processing of emotions by each brain hemisphere. The valence hypothesis theory suggests that left-lateralised individuals (reflecting right hemispheric dominance) are more likely to show fearful and aggressive responses, whereas right-lateralised individuals (reflecting left hemispheric dominance) would be more likely to be calm. Strength of lateralisation, irrespective of the side that is dominant, has also been found to be associated with the intensity of behavioural reactions in novel situations. Because behavioural laterality is rather easy to assess and non-invasive, recent research has focused on using laterality as a ‘readout’ of animals’ emotional processes, stress reactions, and specific personality traits (see also my post on dog laterality).

Ewes and lambs lateral behaviour was associated to their behavioural reactivity during a partial-separation test. Dams and lambs were separated by an open-mesh fence where they could see and hear each other but they could not. Results showed that lateralised lambs and dams spent significantly more time near each other during separation than non-lateralised animals, and that lateralised dams were also more active than non-lateralised ones. Arguably, the lateralised animals showed a greater attrac- tion to their pair because they were more disturbed and thus required greater reassurance. The data show that measures of laterality offer a potential novel non-invasive indicator of separation stress. To learn more about these results, read here Barnard et al. 2015 Animal Cognition.

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