Effect of rare earth elements (REE) supplementation to diets on the carry-over into different organs and tissues of fattening bulls

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 plasma mass 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 increase with increasing dietary REE-citrate supplementation, while the REE concentration in muscle tissue remained unaffected. The highest REE concentration was measured 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/kg DM for Ce and 4-73 µg/kg DM for Pr. The muscle tissue, playing an important role to evaluate food safety, showed the lowest La, Ce and Pr concentrations with 3-5 µg/kg DM, 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.