Metro Council Bill 2011-47 is an interesting bill allowing chickens to be raised within the county (general services district) in certain zoning districts if 5 acres or more in size. if you run a search on Google, you'll find quite a number of articles concerning this issue.
The chickens are permitted in agricultural districts and accessory in residential districts. It appears that if the lot has more than 5 acres, the number of hands is unlimited, but otherwise there is a maximum number permitted of two hands for the first 5009 square feet, four hens for a lot of 10,236 square feet, and 6 hens for a lot of 10,237 square feet or more.
There are several other requirements which must be met concerning the maintenance of the chickens. It certainly will be interesting to see how this new provision fits in an urban zoning classification scheme.