Effects Of Dietary Vitamin E On Immunological Stress Of Layers

In general, vitamin E serves three functions: (1) to eliminate the free radicals, (2) to support the viability of reproductive system, and (3) is used in the food processing. Because of these essential functions, vitamin E is usually added to a commercial layer diet. The applications of vitamin E in poultry production have been well documented. However, there were little reports about the effect of vitamin E on immunological stress of layers. In the present study, two experiments were conducted to evaluate the effect of vitamin E supplementation of a commercial layer (White Leghorns) diet on the laying performance and immunological stress responses of hens.In experiment 1, responses to increased dietary vitamin E levels were evaluated on 270 White Leghorn (WL) layers between 19 and 35 week of age and vaccinated according to 3 ways. The experimental design was composed of 9 factorial treatments: 3 different levels of vitamin E supplementation (0, 40 and 100 IU/kg)×3 stress styles (negative, saline and Egg Drop Syndrome (EDS) vaccine). There were 5 repetitions per treatment, each containing 6 hens. Feed consumption was recorded per pen. Egg yield, egg weight and feed efficiency were measured or calculated once a month. Blood samples were obtained from one bird per repetition before and at 12 h, 24 h, 3 d, 5 d, 10 d, 29 d, 49 d, 69 d after vaccination to determine the antibody titer against Newcastle disease virus (NDV) or avian influenza virus (AIV) and plasma concentration of corticosterone (CORT). When the laying rate reached 70%,egg quality including shell thickness or strength, shape index, yolk color, albumen height and Haugh units were investigated. Results showed that high level of vitamin E supplementation (100 IU/kg) had a beneficial effect on feed intake, egg weight and feed efficiency of stressed hens (P < 0.05), compared with the blank or control group (0 or 40 IU/kg). Although the egg weight was decreased by immunological stress, this trend was not found for feed intake and feed efficiency, which indicated that the supplementation of vitamin E might be advantageous for the laying performance of stressed hens. The antibody titers, egg quality and plasma concentration of CORT were not influenced by the level of vitamin E (P > 0.05). However, there were significant interaction between vitamin E and immunological stress at some time points for several parameters. These results suggested that the effect of vitamin E and immunological stress for layer chickens may have time or age specificity. In addition, Hens suffering immunological stress immediately after EDS vaccination need higher dietary vitamin E intake to obtain maximal level of antibody production.In experiment 2, the negative (A) or saline-injected hens (B) in each vitamin E treatment of experiment 1 were subjected to artificial insemination at 35 week of age. 540 female birds were obtained in all with the combination of A and B group. The experimental design was similar to the experiment 1. The treatment of dietary vitamin E supplementation for these young chickens was the same as their mothers'. 3 different vaccinating ways were those for the first time at 5, 8 and 11 d respectively. The kinds of vaccines and the subsequent vaccinating intervals were identical. There were 5 repetitions per treatment, each containing 12 birds. Feed consumption was recorded per pen. At the metaphase of experiment, each bird was injected celiacly with E. coli lipopolysaccharide (LPS, 0.05 mg/bird). Blood samples were obtained from 4 birds per repetition before and at 12 h, 24 h, 36 h, 48 h and 72 h after administration to measure the antibody titer against NDV or AIV, plasma activity of superoxide dismutase (SOD) and plasma concentrations of interleukin-1 (IL-1) and CORT. At the end of experiment, 3 birds per repetition were selected randomly and were bled from a wing vein to make the blood smear. And then the heterophil to lymphocyte ratio (H/L) was calculated. The results showed that the NDV or AIV antibody titers and the plasma concentration of IL-1 were increased (P < 0.05) by the high level of vitamin E supplementation (100 IU/kg). Likewise, the same trend was found for the vaccinating way of first time at 11 d. Furthermore, there was significant interaction between vitamin E and vaccinating ways on the immune functions of experimental birds. Considered together with the results of experiment 1, the exertion of vitamin E's biological function might be dose dependent, especially its positive effect on the immune responses of laying hens. The supplementation of vitamin E in commercial layer diet under vaccination stress decreased the plasma concentration of CORT and H/L value (P < 0.05), which was in line with the results of experiment 1 and many previous works, indicating the catabatic effect of vitamin E on stress. Vaccinating for the first time at 8 d or 11 d could improve the plasma concentration of CORT and H/L value (P < 0.05), suggesting the occurrence of immunological stress. We inferred this might be one of underlying mechanisms about their promotions for the antibody production.