[Nepeta]

The foal crop theory is about the only thing Sec fans hold onto for dear life. It is a poor theory, especially after c.1880, when the breed stabilized.

Stabilized?

You have noticed the emergence of the Northern Dancer type in contemporary TBs, yes? Northern Dancer was foaled in 1961.

[the OlLine Rebel]

The breed was pretty well established as a breed in its own right by then, instead of a mutt constantly breeding back to horses unknown and arabs and such. That is my main point; other being the breed - indeed, the horse species - cannot improve too much. It is a logarithmic curve, and once you stabilize you are pretty much near the asymptote. Species can only ever get so much better; it’s built-in limits by God. You will never see a horse go 80 mph. So the difference from 1920 to 1970 to 2010 in theory is negligible.