I have found it is better to use chickens as the clean up crew after the garden is spent rather than giving them access to your working garden. What they don't eat they will destroy. You can use chunnels ( chicken tunnel) or a tractor to put them on an empty bed if it needs to be worked during the growing season.
http://www.motherearthnews.com/home...k/chicken-manure-fertilizer-zm0z13amzkon.aspx
http://www.motherearthnews.com/home...k/chicken-manure-fertilizer-zm0z13amzkon.aspx