First, i hope you're not planning to switch them to the layer feed for 2 or 3 more months.
Second, i would definitely recommend that you buy and keep Corid or its equal on hand for when they do go outside, whether they're still on the medicated feed at the time or not.
The medicated starter doesn't necessarily prevent a cocci outbreak. Actually, i'm not sure i've heard of a case when it DID prevent a cocci outbreak, although i expect they exist.
I'm sure your experience will be somewhat different from mine, since our climates are so different, but i would simply keep a close eye on them as spring arrives and they start getting into the dirt. Since you've had a good cold winter, you may find that they are able to easily build up their resistance to the cocci organisms. But just watch carefully for anyone who is lethargic, fluffing up in a warm or secluded area - and of course watch for bloody feces. If you're on the look-out, and you have the medicine already in hand, you can medicate immediately upon seeing symptoms, and avoid big problems.
Does that help you?
