That is one nice horn! Guess I better get out there and attend those barn sales, (if we had any, out here). Looks like it could be somewhat early. My guess is that with the pine butt plug and the carved ring it falls into the first quarter of the 1800s. Could be even earlier. Very nice find. Alas, the hole is a beetle hole, and even if human made would fulfill no purpose. Leave it, or fill it with a good phenolic material to stabilize/minimize the damage. Thank you for putting it out there for the folks to see. I enjoyed seeing it.
Dick