RESUMO
When supplementing lamb diets with vitamin E, an equivalence factor of 1.36 is used to discriminate between RRR-α-tocopheryl acetate and all-rac-α-tocopheryl acetate. However, more recent studies suggest a need for new equivalence factors for livestock animals. The current study aimed to determine the effect of RRR- and all-rac-α-tocopheryl acetate supplementation on α-tocopherol deposition in lamb tissues. A total of 108 Rasa Aragonesa breed lambs were fed increasing amounts of all-rac-α-tocopheryl acetate (0.25, 0.5, 1.0 and 2.0 g/kg compound feed) or RRR-α-tocopheryl acetate (0.125, 0.25, 0.5 and 1.0 g/kg compound feed) by adding them to a basal diet that contained 0.025 g/kg feed of all-rac-α-tocopheryl acetate as part of the standard vitamin and mineral mixture. The diets were fed for the last 14 days before slaughtering at 25.8±1.67 kg BW. Within 20 min after slaughter samples of muscle, heart, liver, brain and spleen were frozen at -20°C until α-tocopherol analysis. Increased supplementation of either vitamin E sources led to a significant increase (P < 0.001) in α-tocopherol concentration in all tissues studied. The tissue with the highest α-tocopherol concentration was the liver followed by spleen, heart and muscle. At similar supplementation levels (0.25, 0.50 and 1.0 g/kg compound feed), α-tocopherol content in the selected tissues was not affected by α-tocopherol source. However, the ratios between RRR- and all-rac-α-tocopheryl acetate increased with the increasing α-tocopherol supplementation (at 0.25 and 1.0 g/kg compound feed), from 1.06 to 1.16 in muscle, 1.07 to 1.15 in heart, 0.91 to 0.94 in liver and 0.98 to 1.10 in spleen. The highest relative proportion of Æ©2S (sum of SSS-, SSR-, SRS- and SRR-α-tocopherol)-configured stereoisomers was found in the liver of lambs supplemented with all-rac-α-tocopheryl acetate accounting for up to 35 to 39% of the total α-tocopherol retained, whereas the proportion of Æ©2S-configured stereoisomers in the other tissues accounted for <14%. Increasing all-rac-α-tocopheryl acetate supplementation was also found to affect the 2R-configured stereoisomer profile in muscle, heart and spleen with increasing proportions of RRS-, RSR- and RSS- at the cost of RRR-α-tocopherol. In all tissues, the relative proportion of all non-RRR-stereoisomers in lambs receiving RRR-α-tocopheryl acetate was lower than RRR-α-tocopherol. These results confirm that the relative bioavailability of RRR- and all-rac-α-tocopheryl acetate is dose- and tissue-dependent and that a single ratio to discriminate the two sources cannot be used.