I wouldn't do something stupid like give it to every single head of livestock in the world (cough) but the great thing about antibiotic-resistant bacteria is that they're not resistant to all antibiotics at once. Without the evolutionary pressure to stay resistant to antibiotic B, a bacteria can be resistant to antibiotic A but not so much A and B at the same time. (Which is why things like MRSA are treated with very old and unpopular antibiotics).

Any new antibiotic makes this approach even better, because if you have A, B, C, D, and now E, now the bacteria has to be resistant to all five at once, which is a lot of useless genes to hold onto.