English Art/Literary Poetry & Literature teen fiction

It's from a story happened in Saskatoon, Saskatchewan, Canada. A boy named Bruce borrowed a rattlesnake as a special pet in reserve at a pet parade. But that rattlesnake scared everyone. The parade was in a mess and Bruce almost lost the rattlesnake. Later he said:

... "If I'd lost that old snake I'd have got my britches tanned from here to Mexico. It belongs to our hired man, and it's been his pet for fifteen years - ever since he was a cowboy down in the Cypress Hills. It's so old it hasn't any teeth, nor any poison either, but he sure is fond of it all the same. It sleeps right with him in his bunk ..."

I can tell from the context that if Bruce looses the snake, sth. serious will happen. But I don't know exactly what "tanned" here means. Thanks.