The Science Behind 'Licking and Chewing' in Horses

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By Sue McDonnell, PhD, Certified AAB Oct 5, 2016

Q. What does “licking and chewing” really mean? Submission? Processing? Relaxing?
Lisa, California

A. Licking and chewing behavior is probably one of the most misunderstood horse behaviors. It simply reflects a change in autonomic nervous system tone that results in salivation that stimulates licking, chewing, and sometimes a big swallow. And that can happen in a number of situations following a threat or disturbance of some sort. To better explain, when an animal or a person is relatively relaxed and engaged in ordinary maintenance activities, such as feeding and resting, the parasympathetic nervous system (the part of the nervous system responsible for the “rest and restore” response) is more or less in control. When an animal or a person is threatened or acutely stressed, the nervous system switches into alert or fight or flight mode with the sympathetic nervous system. Pain, fear, or confusion can all turn on the sympathetic system. When that which turned on the sympathetic state resolves, nervous system control switches back to the more relaxed parasympathetic state.

Horses show some observable behavioral signs of this back-and-forth switching. This cluster of licking, chewing, and sometimes swallowing that you have asked about occurs right when switching back to parasympathetic after a period of sympathetic. That’s because when sympathetic control switches on, salivation ceases and the mouth and lips quickly dry. When the disturbance resolves and relaxation returns, salivation also returns. So the licking and chewing is just that simple reflexive response to deal with the salivation resuming after a period of dry mouth and lips. So, in a sense, licking and chewing do reflect relaxation, but specifically as a result of returning from a spell of acute stress or pain. People often refer to this moment as “relief.” Another medical term for it is sympathetic attenuation...

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