One major risk is mutation. Diseases can mutate just has how we have genetic mutations. The bacteria in the cattle may become immune to the drugs over a long period of time, or mutate and become immune. As we try to fight it with more antibiotics, it may become immune to those as well, eventually creating a bacteria immune to most antibiotics, leaving us unable to fight it, especially in poorer areas, due to the fact that if we did create new antibiotics they would be more expensive than your common antibiotic, such as penicillin.
