A dose response study was carried out to assess the influence of different levels of REE supplementation
on the REE transfer into different organs and tissues of fattening bulls. For this purpose,
48 male German Holstein calves with an average initial live weight of 119±13 kg were divided
into four treatment groups (n=12): one control group and three REE-treated groups fed a supplement
of 100, 200 and 300 mg REE-citrate/kg dry matter (DM) containing mainly cerium
(57.9%), lanthanum (34.0%) and praseodymium (6.5%). The feeding trial was divided into a
growing period (8±3 weeks) and a fattening period (39±4 weeks). The growing diet consisted
of concentrate, grass silage and grass hay, and the fattening diet consisted of concentrate and
maize silage. After slaughtering of the bulls (556±4 kg mean live weight), the concentrations
of REE were measured in the liver, kidneys, Musculus longissimus and rib bone by inductively
coupled plasmamass spectrometry (ICP-MS). The concentrations of REE (lanthanum (La), cerium
(Ce) and praseodymium (Pr)) in the liver, kidneys and rib bone showed a significant linear increasewith
increasing dietary REE-citrate supplementation, while the REE concentration in muscle
tissue remained unaffected. The highest REE concentrationwasmeasured in the liver followed
by the kidneys and rib bone. In the liver, the concentration amounted to 22–482 μg/kg DM for La,
37–719 μg/kgDMfor Ce and 4–73 μg/kgDMfor Pr. Themuscle tissue, playing an important role to
evaluate food safety, showed the lowest La, Ce and Pr concentrations with 3–5 μg/kgDM, 5–7 μg/kg
DM and 0.5-0.7 μg/kg DM, respectively. The results demonstrate that the health risk to humans
consuming edible tissues of REE supplemented animals is very low.