If the grain and other sheep food you feed your flock have contained these antibiotics in the past, or if you've added antibiotics as supplement to your flock's food supply, you don't necessarily have to change what you feed your flock. Those drugs that shepherds have traditionally used will still be available in the United States ... the new rule simply requires that you obtain a written VFD order from a local veterinarian to continue feeding your flock as you have in the past.
If you don't supplement your flock or add antibiotics to the food or water your sheep consume, this rule won't affect you.
The Goals of the VFD Protocol
The goal of the new Veterinary Feed Directive is to make meat raised in the US safer for human consumption, and as a byproduct the government hopes to foster stronger relationships between producers and their local veterinarians. As long as antibiotics in food given to animals are given therapeutically, producers should have nothing to worry about.
Here's a Short Video Discussing the Veterinary Feed Directive from ASI
Final Thoughts about the VFD and How It Will Affect Shepherds in the USA