Don't necessarily despair about your chicken days being over. I treated my ms/mg positive chickens with antibiotics, and after 2 to 3 months, my farm was declared clean. My chickens lived an entire year here with no symptoms. As I said in an earlier post, I eventually decided to trade them in, but I was told directly by an NPIP state-employee that it was unnecessary for me to do so. My hens brooded their chicks successfully and had great laying rates. None showed any symptoms at all. He said I could re-open my flock based on his observations.
But just so you know, if you go through the state (which I recommend because it's a LOT cheaper), you will be registered with the state. They will quarantine your farm and require you to remain closed until you pass a series of inspections. Also, I hope you realize that you have to sacrifice a chicken to get it tested.

It was hard for me.
Also, my experience was that it took longer than 3-10 days for ms/mg to spread. It was slow spreading, and it took up to three weeks before we could be sure it was not still spreading in my flock. As a matter of fact, for the state to declare my farm "clean," we had to wait a full six weeks with no symptoms.
But please don't despair. First get your birds tested (before you panic), then treat them and do everything to keep their coops, feed, and water sources as clean as possible. I changed my chix waterers daily, their nesting boxes and coops regularly, and spoiled them with probiotics and limited healthful treats.
Good luck! mz