Subbing, although there are no Rattlesnakes here in Ohio.
Yes there are, lollol. I grew up in Trumbull County. Massasauga Swamp rattlers abound, when I was a kid.
Believe it or not, they are now on the endangered list. USFWS: Eastern Massasauga Fact Sheet
We were heavily populated with them but there was a bounty on them for their venom, to use as an anti-venum, evidently they got hunted out pretty good.
Their venom was not lethal enough to kill, unless the person already had certain pre-existing health issues.
If you live in the lower one third of Ohio, that may be why you've never heard of them but, believe me, they exist in Ohio. I have seen them with my own eyes when I lived in Trumbull County
As far as desensitizing my horses to them, I dunno. It's never been an issue with any of my horses and we came up on Diamondbacks blocking the maintenance roads, when I lived in SoCal