Horse Side Vet Guide ®

Equine Health Resource

Sick Horse Hyper-Reactive to Loud Sound or Sudden Movement

Code Red - Call Your Vet Immediately, Even Outside Business Hours

Code Green - Contact Your Vet to Obtain Useful Advice & Resources

Code Red - Call Your Vet Immediately, Even Outside Business Hours

  • The horse is down or otherwise showing signs of severe illness.

Code Green - Contact Your Vet to Obtain Useful Advice & Resources

  • If the results of the Whole Horse Exam (WHE) suggest the horse is otherwise normal.

Horse are excitable by nature and startle easily. However, this record refers to a VERY exaggerated response that can occur in horses suffering from particular diseases.

There are neurologic pathways in the brain and spinal cord intended to prevent overreaction by an animal to a stimulus (inhibitory neuronal pathways). If this inhibitory input is lost due to injury or disease, then an animal has exaggerated responses to a stimulus.

A normal reflex requires the following:

1. Functioning sensory organ – the animal senses the stimulus.

2. Functioning sensory nerves – the sensory input is conveyed to the brain by nerves.

3. Functioning brainstem, which receives the sensory input and relays it to the appropriate centers for a response.

4. Motor nerves carry this outgoing signal to the appropriate muscles.

5. Functioning muscles, which contract to form the response.

Vets sometimes use hand clapping or the “menace test” as stimuli to test an animal’s reaction. With respect to a clap, a normal response might relate to how close we are when we perform the clap. An expected response might be a withdrawal from the sound, an ear twitch, or a blink. In a very ill horse, this response may be dulled.

A very exaggerated response to a sudden clapping noise or menace response is classically associated with Tetanus. Horses with Tetanus may become violently rigid or show seizure like signs in response to a loud sound or a startling movement. Their third eyelids may cover their eyes completely for a few seconds and their limbs may become violently rigid.

Like many assessments, these tests are highly subjective and must be interpreted in light of what the observer considers to be a normal response in an individual horse.


This test would probably only be performed on a horse that is otherwise showing signs of tetanus or other disease.

Assess the horse’s general health using the Whole Horse Exam (WHE), paying particular attention to attitude, appetite and normal movement at the walk.

If you are trying to determine the significance of a response, repeat the stimulus multiple times from several locations. By doing this, you begin to desensitize your horse to the stimulus. If the horse becomes decreasingly sensitive to your clap, and they show no other signs of illness or abnormalities, this is most likely a “normal” response.

However, if the horse continues to exhibit an excessive or abnormal response, or if you are still concerned, call your vet to discuss your findings and concerns.


Your vet will try to determine whether the horse’s response to the stimulus is normal or not.

They consider the horse’s response in combination with their findings on a general exam to determine whether this sign is really indicative of illness or is considered normal for that horse.

Author: Doug Thal DVM Dipl. ABVP


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