That was very interesting. I checked some other sources and luckily only 1-2 percent of horses died but this outbreak brought the nation to a complete halt.
It's interesting that, due to the mechanization of agriculture (thanks in large part to Henry Ford), and despite a large increase in the US population, the amount of land under cultivation declined overall in the first half of the 20th century, since the horses didn't have to be fed whether working or not.
I never saw this on Gunsmoke.