A feeding study was performed to investigate possible performance enhancing effects of rare earth elements (REE) in growing and fattening pigs, as well as their influence on the blood serum biochemical changes and the accumulation of REE in the organs of pigs treated with a REE diet for a longer time period. Fourteen crossbred piglets (Deutsche Landrasse x Pietrain) were allotted to two dietary treatments: a control group and the REE-treated group which was supplemented with 300 mg of an REE mixture per kg feed. The REE mixture contained mainly chlorides of lanthanum (La), cerium (Cc) and praseodymium (Pr). The whole feeding period consisted of a 2 months ad libitum feeding period M-I and a 1 month restricted feeding period M-II. It was found that in comparison with the control group, the REE group had a better daily body weight gain of 19% (p < 0.05) in the period M-I and 12% in the period M-II; the REE group also had a better feed conversion ratio of 11% in period M-I and 3% (p > 0.05) in the period M-II. The REE had no significant (p > > 0.05) influence on blood serum thyroxine (T-4), aspartate-amino-transferase (AST), alanine-amino-transferase (ALT), alkaline-phosphatase (AP), total cholesterol, triglyceride, total protein, albumin, glucose, Ca, P, Na, K and Cl. However, serum triiodothyronine (T-3) in the REE group was significantly (p < 0.01) lower than that in the control group. The accumulation rate of La and Cc in the muscle, liver and kidneys was very low after feeding the REE diet for 3 months. The study indicates the possibility of using rare earth elements as safe and inexpensive alternative performance enhancers for pig production.
