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A. This is actually a question that could have quite an expansive answer. Headshaking can take lots of forms:

• The head toss seen with play behavior and inter-male aggression;
• The occasional shake seen after rolling or with insect avoidance;
• Rhythmic nodding; and
• Excessive, troublesome headshaking during work

We do see some horses that standing at rest in their stall perform a rhythmic, unchanging, vertical nodding. This seems to be a stereotypy much like other movement stereotypies in confined horses, including weaving. This should be distinguished from more dramatic and sometimes debilitating headshaking that may include incessant vertical tossing of the head, frequent snorting, and urgent attempts to rub the nose.

Both of these types of horses should first have a thorough physical exam by a veterinarian. A certain number will have a diagnosable medical condition causing this behavior, including bone, dental, sinus, or eye problems. Some could have persistent irritation from parasites or vegetation such as foxtails. Tack should be investigated, but unfortunately that is not so commonly the cause of the severe head shaker