Horse Side Vet Guide ®

Equine Health Resource

Change in Personality, Strange Behavior

Code Orange - Call Your Vet at Their First Available Office Hours

Code Yellow - Contact Your Vet at Your Convenience for an Appointment

Code Orange - Call Your Vet at Their First Available Office Hours

    Code Yellow - Contact Your Vet at Your Convenience for an Appointment

    • If this seems mild or occasional and the horse seems normal otherwise.

    This is a very general statement but one that I hear fairly frequently from my clients. My first task is to engage the horse owner in a thorough history, asking as many relevant questions as needed to gather more specific information.

    Occasionally, a horse will act in a mysterious or atypical way, a personality change that may be hard to describe. Change in environment, new handlers, riders or management, all can contribute to an apparent change in personality. Physical problems can also manifest as atypical behavior. The behavior might include aggression toward horses or humans, depression, eating less than usual, misbehavior under saddle, or dozens of other variations.

    Behavior is mostly controlled by the forebrain. Forebrain disease therefore can cause all sorts of behavioral changes, depending upon the specifics of the condition. Forebrain function can be affected by diseases of the brain itself, toxins in the blood, low blood sugar, blood loss, and liver dysfunction, among many other problems.

    Hormonal changes in stallions and mares affect behavior. Pain causes behavioral change too. If there is a possibility that physical issues could contribute to the behavior change, then your vet may be able to help you rule those out. If your vet has ruled out physical causes, and you do not feel confident identifying and changing the behavior, then you may want help from a qualified trainer.


    Assess your horse’s general health using the Whole Horse Exam (WHE), paying particular attention to attitude and appetite and the vital signs, including rectal temperature, heart rate and respiratory rate. Share your findings and concerns with your vet.

    NOTE: This observation is associated with Rabies, which is very rare in horses but does occur. As a precaution, wear gloves when handling a horse exhibiting this sign.


    Your vet takes a careful history and observes the horse’s behavior. A thorough physical exam rules out certain conditions. Depending upon the results of these tests, they may suggest other diagnostics.

    POSSIBLE TREATMENTS or TherapiesTo Lessen or Resolve the Sign

    Author: Doug Thal DVM Dipl. ABVP


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