So I went to the conclusions of the very first of your citations which essentially says the compound is safe at approved doses. As I wrote "the dose makes the poison". We eat thousands of natural compounds safely every day which at high concentrations cause adverse effects. Insinuating that this citation backs up any assertion that this compound is unsafe as used in feed is fear mongering. If any of the other papers suggest that current approved uses are unsafe, please feel free to repost those. And as your last citation shows, even a required nutrient like iron is toxic if ingested at very high concentrations. Risk = Hazard x Exposure.