The FDA first proposed withdrawing Baytril in October of 2000, due to concerns regarding the development of antibiotic resistance. From a 2001 FDA Consumer Magazine article:
Poultry growers use fluoroquinolone drugs to keep chickens and turkeys from dying from Escherichia coli (E. coli) infection, a disease that they could pick up from their own droppings. But the size of flocks precludes testing and treating individual chickens–so when a veterinarian diagnoses an infected bird, the farmers treat the whole flock by adding the drug to its drinking water. While the drug may cure the E. coli bacteria in the poultry, another kind of bacteria–Campylobacter–may build up resistance to these drugs. And that’s the root of the problem.