I was about to say make sure they can huddle up to keep each other warm, so I'll be interested in Castle Farm's views, too!
The other thing was to give them maize as well as corn - it's very heating, so to be avoided in summer but really helps them maintain their body temperature in cold weather.
(Of course if you are American, maize is corn, but we tend to mean 'grain' generally when we say [hen]corn.)