Rare earth elements (REE) as feed additives in animal nutrition.

Abstract After providing a brief historical survey of the use of rare earth elements (REE) as feed additives, the authors of this review attempt to analyse the implications of REE in animal nutrition; they demonstrate the results of a variety of efficacy studies in food producing animals and consider REE-residues in organs and tissues of such animals. The results of those studies are as inconsistent as their approaches and as REE or compounds of various REE applied in the presented investigations. Current research data do not yet reveal if REE are essential to animal metabolism. Furthermore, we don't know so far the exact functions of individual elements and mixtures of REE concerning animal metabolism and yield. As results are inconsistent, no general economic implications can be predicted either. It is proposed that future research should focus on individual REE before investigating the effects of defined REE-mixtures. Apart from determining possible mechanisms and potential effects of REE in more detail, further studies might explore long-term effects and should also be conducted with regard to food safety and environmental aspects.