She's not afraid

Those were more or less the words used when a friend of mine explained that the vet did not think fear had any part in her young mare's abrupt aggressive behaviour. The vet's reasoning was that there was no increase in heart rate to accompany what were ostensibly defensive acts. Defensive because they were triggered by a situation that the young mare had previously linked to pain. Her resulting behaviour was intended to relieve her of the person provoking her distress - the vet.

My question is however, if the heart rate doesn't increase, is fear truly absent? I will explore some of the neurophysiology behind the behaviour.

Increased heart rate is a classic symptom of the fright, flight, fight response. A reflex response driven by the sympathetic branch of the autonomic nervous system.

The subconscious takes note of what was happening right before the event, logging the most notable as warning signals for the future, and also remembers the actions that led to successful escape. It is in the future when the now learned warning signals prompt successful evasive actions, providing the horse with a sense of control they didn't have before. This sense of control gives confidence and calmer execution of behaviour, even evasive behaviour.

This happens because successful actions enable the horse to deliver herself to safety and a state of relief. From there she can continue her usual daily activities.

However the warning signals are still threatening, so fear has not completely left the horse. When avoidance actions are not instantly effective, and/or when the same threatening situation keeps presenting itself, frustration and anger join the emotional mix. Naturally these states drive more aggression more readily.

Going back to the mare in our example. She had been repeatedly exposed to the same sequence, injury/ill health, veterinary examination and procedure,  more/worse pain. Even when examined in passing, when not already in pain, she doesn't get defensive at the end of the examination, she takes action before then: When the vet appears to examine her.

Now that she has practised getting rid of the vet and successfully escaping and avoiding further painful intervention, she is more confident of success from the outset - so doesn't need to get her heart rate up. However, because she is a naturally easily frustrated horse, her early vet fighting episodes mixed anger into her reactions regarding examination. This means that her defensive strategy of choice includes aggression and she resorts to it sooner rather than later as she is confident in its chances of success.

So is she afraid? Yes, vets equal pain! Plus, she is also downright outraged that the vet continues to darken her door. But she also knows exactly what to do about it. So she doesn't put any more energy in than is strictly necessary.