07/22/2025
Excellent article
Trigger stacking and why it is so relevant for safety when handling horses.
What is trigger stacking?
Trigger stacking describes the process of multiple stressors accumulating and increasing the stress level of an animal until they can no longer cope, resulting in an outward reaction.
The triggers can vary in intensity. But the nature of trigger stacking means that the final trigger that results in a major reaction in the horse does not always have to be a big trigger. It can be the straw that broke the camel’s back.
This phenomenon is why horses may sometimes appear to react out of nowhere or have a strong reaction to something that, in other circumstances, they might not be bothered by at all or as bothered by.
In other cases, the triggers in the environment might be so large that the horse reacts suddenly following one big high intensity trigger. A very scary moment.
But, in many cases where horse behaviour surprises people, and they cannot assess the cause, it is the result of multiple smaller triggers.
Let me give a great example of trigger stacking that I witnessed happening at the racetrack.
A pony Horse was being tacked up, tied to the wall in the middle of a shedrow.
Since he lived at the racetrack, he was stalled 24/7, which would serve as a chronic and rather large trigger.
It was shortly before the first race of the night and the barns were very busy with lots of horses walking to and fro. The hectic environment serves as multiple smaller triggers.
There was a fan in the aisleway oscillating back-and-forth.
Every time the breeze hit this horse, I watched him tense up, raise his head and flinch.
Every single time this fan hit him was an additional trigger.
Finally, the last trigger before his big reaction.
Someone picked up and moved the fan.
It was unplugged, so there was no breeze.
But, they moved a little too close to this horse, and the base of the fan just barely skimmed his leg.
This horse, who had already been a picture of tension before, exploded.
He pulled back against his tie, and when he felt the restriction of the rope, he panicked even more.
He pulled until his halter broke.
Then he froze and stood there trembling.
“ wow, what’s his problem!? He did that out of nowhere.” One of the handlers of this horse exclaimed.
But, he didn’t do it out of nowhere. They had just missed all of the signs of his tension growing, and because of that his reaction came as a surprise to the humans.
I watched the whole thing happen from a distance because it was not my horse, and I also had increasing anxiety as I watched how uncomfortable this horse was getting.
I knew a reaction was imminent and his response did not surprise me.
In horse training, a lot of times people feel like horses react out of nowhere.
But, the truth is, we are often just bad at noticing the earlier signs.
If people wear more in tune with the body language, their horse displays, the subtle size, in addition to recognizing the signs of stress, they would be more able to predict behaviour like this and avoid it in the first place.
Being aware of what trigger stacking is as well as the science of stress in horses is imperative for safety around horses.
A lot of the incidents that we see with horses are technically avoidable, whether or not people want to admit it.
There are almost always signs, training methods, and management factors that could be addressed to avoid dangerous reactions in horses.
While there are situations where the environment is so out of control that people are truly helpless to make changes to avoid really dangerous responses from the Horse, this does not happen as often as people might think.
So, next time you feel like your horse has reacted out of nowhere, ask yourself what might have triggered their flight response.
Start taking note of all of the things that happened just before the reaction.
Start looking critically at your Horse’s day-to-day life, and whether or not they are experiencing chronic stressors like lack of turnout, or physical pain.
And remember, just because you did not notice the signs, does not mean that the horse reacted out of nowhere.
