When I read that section of the code what I got out of it was that animal byproducts could not be fed to ruminants, not that ruminant couldn't be fed to chickens. That was only from one section of the code. Will take more research for poultry feed.
http://www.access.gpo.gov/nara/cfr/waisidx_00/21cfr589_00.html
http://www.access.gpo.gov/nara/cfr/waisidx_00/21cfr589_00.html