Silkes with large fowl
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It hardly gets above freezing (32 degrees) here in winter and I've never had to add heat to my coop.
I have silkies with my large fowl with no problems. I have bantams that fit in the palm of your hand up all the way up to large fowl, including guineas and turkeys, all together in a large pen. Just make sure you have enough space that they can move away from the larger birds if they want/need.