Russian Race Horses

Hate to do it to you, Doug, but this question actually occurred to me during a meeting ... and I instantly thought of you.... :)
Frantically preparing for an impending meeting, Dinley was panicking and said "I've got to [urinate] like a Russian Race Horse." And off he went.
Q: So, the question is, naturally, how did this association come about? Are Russian Race Horses notorious for massive amounts of pee? Or do they have trouble holding it?

A: This answer was so good, I had to quote it directly from the source, The Phrase Finder: "All horses urinate visibly, audibly and above all copiously, and presumably this is an occurrence highly noticeable at a race meeting when the competing horses are led around the parade ring for the crowds to examine before the off."

This, of course, leaves the "Russian" element out, but covers the basic phenomenon. I was surprised at the number of people who seem to be seeking the answer to this same question online. It's not a meme I would have expected. At any rate, there doesn't seem to be an agreed-upon answer for "why Russian race horse", but there was a suggestion (probably untrue) put forward. According to one source (who heard it from a guy, etc.), Russian horse trainers used to uh,... tie off their horses before a race, thinking that they would run faster if they really needed to go, and that they could expect to be allowed to relieve themselves at the finish line. I tend to doubt this, as much because I doubt a horse would be allowed to spatter judges and happy well-wishers with "copious" urination at their moment of glory, but mostly because I can't imagine that I myself would run better under those conditions.