Many domesticated animals show increased growth and improved feed efficiency when given low doses of antibiotics. In fact, this is by far the biggest use of antibiotics. Mostly you hear about this in the context of worries about how this may select for resistant bacteria (which may well be true), but one interesting question is why it even works – and what other applications this technique might have.
It strikes me that it might be useful in food emergencies – famines and so forth. The dosage is low (200 g per ton) and can increase feed efficiency over 10% in some cases. Assuming that antibiotic supplementation works in humans (which is likely, considering that it works in a wide spectrum of domestic animals), you might be able to save 5 or 10% more people with a given food supply. Now if we ever bothered to learn exactly how this works, we might be able to find an equivalent approach that didn’t use antibiotics, some other way of knocking out certain pathogens (phage therapy?) or altering the gut flora.