Are cowboy boots meant to prevent snake bites and to step in poop?

No. They are made to fit the stirrup on a saddle and provide full foot and ankle protection below the chaps.

Yes and to keep the shoes from slipping out of the stirrups

They are also good for kicking cow poop out of the way. We used to call them “shit kickers” and people who wore them, “kickers”. But they called us “hippie stoners” or “slackers”, so to each his own I suppose. Not that the kickers worked any harder in school than we did.

The heels are designed to have enough heft to kill a rattlesnake by stomping on it.

And don’t forget boots with spurs – the spurs transmit leg movements to the horse to prod it to move or stop.