I think that it's everything together. Basically, giving animals antibiotics means that you have more animals (and animal weight) which can be sold at market.

I think that it's everything together. Basically, giving animals antibiotics means that you have more animals (and animal weight) which can be sold at market. If it were more expensive to give antibiotics to the animals, farmers might rethink the equation, deciding to instead raise more, smaller animals in more sanitary environments. Michael Pollan's excellent book, "The Omnivore's Dilemma," describes at great length the way in which non-factory farms operate, and why he believes they don't need the same sorts of sanitary rules that the government places on factory farms. I have no way of knowing whether he's right, but there's definitely some logic to the claim that antibiotics are addressing the symptom, rather than the root cause.