Interesting. @SouthernStorm do you have any more specifics on what they say is lacking from organic feeds, and is it all organic feeds? I'm happy to dig into this myself if you would rather just point me to a source. I'm always interested in learning more. (Weirdly, I don't seem to have much Nutrena around here.)
I got the information at a lecture with the Purdue DVM specialists, so there isn't a website I can point you to, but I think the reasoning behind it is that for any feed, animals, eggs, etc. to carry the label organic, they can not have any access to additives or coccidiostats that are found in most standard or medicated feeds in order to promote healthier chicks. As a result, if your peeps get coccidiosis or any other illness, you can't treat them without breaching the rules of organic labeling. You also can't feed them any non-organic treats, including store bought mixes, kitchen scraps of non-organic produce, grains, etc. without doing the same. You could probably email someone through the Purdue poultry extension to explore further. I hope I didn't hear them wrong during the lecture.
My suggestion would be to talk to other chicken owners in your area and see what feeds they are using and what is available. I use Flint River Mills (FRM) which is only available in the S.E. U.S. but I know some of the farms used as test farms for their feed formulation and I do show my birds at poultry shows. I have used Nutrena many years ago.