Transfer of α-tocopherol stereoisomers in laying hens from feed to egg yolk and tissues of hatched chicken

Alpha-tocopherol (vitamin E) derived from natural source consists solely of a single stereoisomer (i.e. RRR-alpha-tocopherol) while synthetic vitamin E consists of a mixture of eight stereoisomers (all-rac-alpha-tocopherol). These stereoisomers are not equally retained in the body and their efficiency of utilization differs amongst animal species. A study with laying hens was carried out to determine the transfer of different alpha-tocopherol stereoisomers from feed to egg yolk and various tissues of newly hatched chicken. The results of this study show that the alpha-tocopherol stereoisomer composition of egg yolk and various tissues of newly hatched chicken are closely related to dietary vitamin E sources. When all-rac-alpha-tocopheryl acetate is supplied to feed, 2R forms are preferentially transferred to egg yolk and tissues as reflected by an increase in the 2R/2S ratio. Discrimination of different isomers is related to dose level and target tissues. Brain turned out to be the most discriminating tissue amongst tissues tested in this study. Low dose levels of all-rac alpha-tocopherol result in relatively higher RRR isomer retention in tissues. The degree of stereoisomer discrimination is less pronounced in laying hens compared to pigs and ruminants. However, a tissue specific discriminatory mechanism for selecting different alpha-tocopherol isomers appears to exist also in layers.