Does brain lateralization have practical implications for improving animal welfare?

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Abstract Many vertebrate species are known to have a similar pattern of brain lateralization, often expressed as eye preferences or side biases. Fear and aggression are specializations of the right hemisphere, expressed as left-side biases. The left hemisphere categorizes stimuli and follows learnt rules of behaviour. Here, it is argued that eye, ear and nostril preferences could be useful in interpreting cognitive processes of individual animals and beneficially applied to predicting behaviour and improving welfare. Knowledge of lateralization may be particularly useful in reducing accidents involving large animals (e.g. flight and aggression of horses is stronger on their left side). The right hemisphere is highlighted as being important in welfare since its activity involves stress responses and the expression of intense emotions. It is hypothesized that a balance between left and right hemisphere activity aids welfare by preventing aggression, excessive fear, depression or negative cognitive bias. Ideas on how a balance between the hemispheres might be reinstated in animals suffering chronic stress and persistent right-hemisphere dominance are discussed. Limb preferences may reflect hemispheric dominance and be associated with different temperaments or personalities, as first found in primates. A relationship between limb preference and temperament, as well as state of health, is also present in four-legged animals. Lateral biases in moving a medial appendage, as seen in the tail wagging of dogs, can indicate which hemisphere is dominant and could be a social signal valuable in assessing welfare. In conclusion, knowledge of lateralization may be applied constructively to improving animal welfare.