I don't know where your flock is, but here in Maine, I've got a foot of snow still on the ground (groan) and several boxes of soil with wheatberries growing on windpwsills
in the house. When they sprout and grow to about three or four inches, I bring them out to the chickens. They love it. I've also used winter rye berries, annual rye, barley-whatever I find at the farm store.
I put about three inches of soil in an empty container that those expensive lettuces come in this time of year, spread the seeds in rather thickly, water, and in a few days, things start happening. It's a cheerful site on the windowsill for us, and when it goes outside, the chickens work it over within minutes.