None of these other posters account for what would cause a flock to stop free ranging? Old hens - no winter eggs - possible. Old hens always free range in winter months.
My old girls don't, they have a pasture to themselves but in the winter if it's too cold, wet or windy they'll just go down and sit around under their favorite cedar tree all day. There's really very little for them to eat in the winter, so why bother.
I wouldn't consider no eggs from only three 3 year old hens all that odd. We get spoiled by all the eggs they give us for the first two years, but a severe decline around 3 is not unusual in my experience.
Could it be that the feed was old? Might have been several months old when you got it (always make sure to check the manufactured on date!) then I imagine it takes a long time for only 3 girls to go through a bag of feed.