Q: I took care of an issue with feather loss in my flock, so why haven't my chickens' feathers haven't grown back?
A: Not necessarily. Sometimes hens will regrow feathers immediately, and sometimes they won't regrow missing feathers until the molt (usually in the late summer or fall). The best layers are usually using all their resources to produce eggs, rather than to regrow feathers.
That means high-production layers are generally the types that may not refeather immediately.
To help your birds regrow missing feathers, you may consider getting a higher protein feed for a while; they need lots of protein to grow healthy feathers!