Effect of graded levels of rare earth elements in diets of fattening bulls on growing and slaughtering performance, and on nutrient digestibility of wethers.

The aim of the present dose response study was to examine the long-term effects of increasing the amounts of rare earth elements (REE) in the diet on growth and slaughtering performance of fattening bulls. A total of 48 bulls of German Holstein with an average initial live weight (LW) of 119 + 13 kg were divided into four dietary treatment groups (n = 12): a control group and three REE-treated groups, which were fed a supplement of 100, 200 and 300 mg REE-citrate per 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 for 8 weeks and a fattening period for 39 weeks. The growing diet consisted of concentrate, grass silage and grass hay, while the fattening diet consisted of concentrate and maize silage. The animals were slaughtered at approximately 556 kg LW. The intake of grass hay and maize silage (0.55-0.31 kg/d and 6.09-5.44 kg/d, respectively) decreased linearly (p < 0.05) with increasing REE-citrate supplementation, while LW gain showed only a numerical decrease during the growing (2-4%) and the fattening period (4-5%). The feed-to-gain ratio and ME-to-gain ratio were not significantly affected by REE treatment during the whole feeding trial. The most striking effect of REE on carcass characteristics was a significantly higher dressing percentage in Group C (200 mg REE citrate kg/DM) compared to the other groups, while no effects were found on liver, kidneys, heart, thymus, pancreas, spleen and thyroid gland weights. The digestibility trials with wethers indicate that a supplementation of 300 mg REE-citrate per kg DM to a ration consisting of concentrate and straw does not enhance the digestibility of nutrients. These results suggest that, under the conditions of the present study, the supplementation of fattening bull diets with REE cannot be recommended.

Effect of rare earth elements on beef cattle growth performance, blood clinical chemical parameters and mitogen stimulated proliferation of bovine peripheral blood mononuclear cells in vitro and ex vivo.

Rare earth elements (REE) are possible performance enhancers in animal production, but little is known about their effects on ruminants. Therefore a feeding trial was conducted with 40 fattening bulls who received 0, 100, 200 or 300mg REE-citrate/kg dry matter (DM), containing 34.30% La, 58.09% Ce and 7.61% other REE. DM intake was measured daily and live weight weekly. Ex vivo ConcanavalinA (ConA)-stimulated cell proliferation of peripheral blood mononuclear cells (PBMC) was tested by MTT and alamar blue (AB) assay. Serum was analysed for clinical chemical parameters, ion (Mg, Ca and P) and REE concentrations. The effects of LaCl(3), CeCl(3), NdCl(3) and YCl(3) on ConA-stimulated proliferation of PBMC were tested in vitro, using MTT and AB assay. REE-citrate supplementation did affect DM intake, but not live weight gain, clinical chemical parameters, and ion concentrations significantly. In REE-300 group ex vivo proliferation of PBMC was significantly increased. In vitro ConA-stimulated proliferation decreased with rising REE-chloride concentrations. At least at the highest tested concentration (approximately 290µM) the inhibition reached significance. Proliferation of non-stimulated PBMC was not affected dose-dependently. REE affect the proliferation of PBMC, thus an effect on the bovine immune system is possible. However, the great differences in effective doses in vitro and ex vivo (serum REE concentrations) might explain the different results from the experiments.