Of course it’s not the size of a walnut! That’s a ridiculous old saying, hence the quotation marks!!

RE: The Size of a Walnut’ – Does Equine Brain Size Matter?
I’m just a layperson, but I have been looking into this topic for awhile.
The Cozzi study showed large variations of EQ in horses, ranging from .50 to 1.3 The higher number is in the range of primate EQ.
Another study aspect is in animal innovation- how the animal deals with situations outside of what it encounters in its wild environment. My horse opening latches and untying lead rope knots would be examples. No knots or latches on the primeval russian plains!
Next, the mirror test. Some have used it as a self-awareness test. Humans, dolphins and elephants apparently pass this test. In a 2021 study it appears that the horses as a group passed it as well: https://link.springer.com/content/pdf/10.1007/s10071-021-01502-7.pdf
Lastly- brain the size of a walnut? The brain of a horse is half the weight of a human brain. The horse’s cerebral cortex is about 2/3 of the brain total weight. I have never in my life seen a walnut anywhere near that size.
Now, can somebody tell me the EQ of my mule? 🙂

I see what you’re saying re training, but the point is that what you’re describing with instinct and reasoning are observed behaviors – not something wired into one or the other hemisphere of the brain. Right brain vs. left brain is more a cultural concept than a neuro-anatomical one. If the cultural concept helps the trainer, then fine.

I’ve added in an extra line about assessing intelligence in horses, so thanks for that prompt. I had already written that intelligence is hard to define in horses, although that statement was further down the article… I guessed you missed it 😉

Thank you for the exellent article by Evelyn B. Hanggi; Mind the horses Mind. The article left-right-brain (logic vs creativity) covers the human field handedness and brain asymmetry. It is not what I meant. In horses you find predispositions to react more instinct related ore reasoning related. Instinct related means: submissive, fearful, not confident, nervous, reactive. Reasoning predominant means: dominant, brave, confident, calm. It’s a general estimation and offers to the trainer to handle more individually with a horses character. The extreme of both sides is rare. The goal is to come from one side to the middle. We call it right-brain or left-brain predominance. To give horses the opportunity to occupy with mental related stimuly is of great benefit to them and will be balancing the extremes.

This is not a scientific medical research article, but thanks for pointing it out. The walnut phrase has commonly been used in popular culture, which is why it’s mentioned here. Try googling it – this may help for starters http://www.equineresearch.org/support-files/hanggi-mindthehorsesmind.pdf

Recent research shows that the *popularly* held belief in a left brain / right brain dichotomy (logic and reasoning vs creativity and intuition) is unreliable. This is worth a read https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001767

And yes, OF COURSE intelligence is hard to define and therefore measure across different species. With animals, we can only measure responses that are given to human made scenarios.