(“I can’t define it but I know it when I see it.”)
The International Dressage Riders Club is international in the same way that the Bangor, ME, airport is. So the members are from all over the map but not necessarily “International Riders,” if you get my drift. Consequently on their discussion page they get pretty silly at times, to wit: “Is it possible to judge if a horse is a Happy Athlete? How do you measure something as intangible as happiness and how do you define it?”
In case you’re unaware, this refers to the updated verbiage in the FEI’s Object and General Principles of Dressage, generally seen as an intent to emphasize Harmony in the horse’s training and showing (as does the introduction of the phrase Willing Cooperation to make Submission less evocative of Subjugation.)
It’s not so much an effort to redefine goals but rather some additional reminders to keep us all on the right path. And it’s probably a hedge against the always-looming ire of the PETA people of the world.
So to the question at hand—There are two ways to answer it. We can posit optimal respiration rates for a “happy” horse and graded acceptable levels of tail pinwheeling. Maybe chart decibel and frequencies observed in teeth grinding, and so on. Or more practically we can adopt Supreme Court Justice Potter Stewart’s reply when asked the definition of pornography—”I can’t define it but I know it when I see it.”
Without being too cheeky here, if you can’t recognize it without a formal definition, you probably aren’t much of a horse person (and you might be defective in a larger sense as well)! Somewhat like a marriage, happy doesn’t imply that either party always gets what it wants or that there’s never a cross moment. This IS training, after all, and both parties may be fairly opinionated at times. But if it’s a viable working relationship that both participants look forward to, that sounds happy to me!