Im sure there are a few places in India and China that still do it where alfalfa is expensive while antibiotics cost pennies. But it certainly isn't happening in the US where growing grass is as close to free as anything gets but antibiotics cost a decent amount of money. A 800 pound cow is only worth around $250 pounds to a farmer, so even a 30% increase, which is far beyond optimistic, is at best going to net you $75 extra, which is not going to cover the many months worth of antibiotics it took to dose an animal that large.