A note on the effect of rare earth elements on the performance and thyroid hormone status of rearing piglets

Rare earth elements (REE) have been used for decades in China to promote growth in plant production and farm animals. Studies are presently also being conducted under Western animal production conditions, however dose-response studies are relatively rare. In this study a total of 80 piglets were fed a diet supplemented with 0, 100, 200, 400 or 800 mg of citrate-bound rare earth elements, consisting of, %: lanthanum 30, cerium 55, praseodymium 5 and neodymium 10. The trial lasted 35 days, the initial mean body weight of the piglets was 7.2 kg. Apart from growth and feeding parameters, blood serum was analysed for T₃ and T₄ by radioimmunoassay (RIA). Feed intake decreased insignifi cantly with higher REE-levels. The daily weight gain of piglets amounted to 283 (control), 301 (100 mg), 254 (200 mg), 258 (400 mg) and 271 g (800 mg). Thyroid hormone levels increased with REE-supplementation. More dose-response studies will be necessary to prove the effects of REE on growth parameters and their intermediate effects.