ABSTRACT
This study evaluated the biological discrimination of different alpha-tocopherol stereoisomers (i. e. RRR-, RRS-, RSR-, RSS- and the four 2S-alpha-tocopherols) from all-rac-alpha-tocopheryl acetate supplementation in milk replacer for rearing and veal calves respectively, in practical farming conditions. Two experiments were conducted. In experiment 1, six rearing calves were fed milk replacer supplemented with 80 mg/kg all-rac-alpha-tocopheryl acetate for a period of 9 weeks. The calves were supplied calf starter concentrate from 1 to 12 weeks. In experiment 2, six veal calves were fed milk replacer supplemented with 80 mg/kg all-rac-alpha-tocopheryl acetate for a period of 24 weeks. Blood samples were taken at the start and every 4 weeks until 12 weeks for rearing calves in experiment 1, and until slaughter (24 weeks) for veal calves in experiment 2. Liver, adipose, muscle, and brain samples were taken at slaughter of the six veal calves in experiment 2. The distribution of different alpha-tocopherol stereoisomers in feed, plasma, and tissues was analyzed. In both experiments, it was observed that RRR-alpha-tocopherol was the dominant stereoisomer in plasma and tissues. The average percentage of the RRR-alpha-tocopherol stereoisomer was 64 %, and 39 % of the total alpha-tocopherol in plasma for rearing and veal calves, respectively. The higher RRR-alpha-tocopherol stereoisomer proportion as percentage of the total alpha-tocopherol in rearing calves was related to higher dietary natural vitamin E intake. Other 2R-alpha-tocopherol stereoisomers had lower utilization efficiency than RRR-alpha-tocopherol stereoisomer. 2S-alpha-tocopherol stereoisomers were basically not utilized by calves.
