One of the links for the Mother Earth News articles that is a good reference point: http://pdf.usaid.gov/pdf_docs/PNADQ897.pdf
Making your winter feed now: silage - Page 3
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White clover is by far the best forage crop for chickens. It is very high in protein and doesn't contain the toxins that can develop in other clovers. It is short and easily mowed/collected for silage and hay (I make both for my girls) and can be mowed several times in a summer without causing it any harm. An added side advantage it that our bees love it as well when it flowers.
I have friends that bag their lawn clippings.
I take them and make silage.
I feed the silage during the winter months, they seem to like it, but then again, there is little else available except their pellets...