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Effects of dietary vitamin E on immunological stress of layers and their offspring.

In the present study, two experiments were conducted to evaluate the effect of vitamin E (VE) supplementation of a commercial layer diet on the laying performance and immunological stress responses of hens and their offspring. In experiment 1, responses to increased dietary VE levels were evaluated on 180 White Leghorn layers between 20 and 35 weeks of age. There were three levels of VE in the diets (0, 40 and 100 IU/kg) and five replicates per treatment, each containing 12 hens. Results showed that the high level of VE supplementation (100 IU/kg) had a beneficial effect on feed intake and feed efficiency of hens (p < 0.05), compared with the VE-deficient or low-level group. In experiment 2, 540 female progeny from the VE-treated hens in experiment 1 were used. The experimental design consisted of three levels of VE supplementation (the same as their mothers') × 3 vaccinating routines, the first vaccination being administered on day 5, 8 or 11. All vaccines and the subsequent vaccinating intervals were identical. In the interim of the experiment, each bird was injected celiacly with Escherichia coli lipopolysaccharide (LPS). The results showed that antibody titres against Newcastle disease virus (NDV) or avian influenza virus (AIV) and the plasma concentration of interleukin (IL)-1 were increased by the high level of VE supplementation. There were significant effects of the day of initial immunization with infection bursal disease on the NDV and AIV antibody titre, H/L ratio and plasma concentration of corticosterone and IL-1 before and after injecting LPS, suggesting the occurrence of immunological stress. There was also significant interaction between VE and vaccination routine on the immune functions of experimental birds. Considered together with the results of experiment 1, VEs biological function appeared to be dose-dependent, especially with regard to its positive effect on the immune responses of young chickens.