What I know more about is the pork industry, because that's what I really spent some time on. They wean their pigs a little bit later than they tend to here. They use the probiotics. They use what are called organic acids, so the proprionic acid, which seems to work as well as the antibiotics for promoting growth in their hogs.
Even though there are very industrialized methods of growing hogs, they don't have the hogs quite as densely populated as is common on this continent.
I'd also point out that there's been a lot of talk about ionophores today, but the realities are there is penicillin, there are tetracyclines and macrolides--tylosin, which is similar to erythromycin--that are also used non-therapeutically and for growth promotion in livestock.