Broiler chicken responses to immunological stimuli as mediated by different levels of vitamin E in the diet

SUMMARY An experiment was conducted with broiler chickens from 1 to 36 d of age to test the effect of 30, 65, or 100 mg/kg of vitamin E in the diets of birds either vaccinated against coccidiosis (VaCC) or not vaccinated. All birds were vaccinated against Newcastle disease to verify the antibody titers generated by the different treatments. Performance and immunological parameters were evaluated. There was a significant interaction between VaCC and vitamin E level: VaCC birds consuming 65 mg/kg of vitamin E showed better BW gain for the total experimental period, lower values for the heterophil:lymphocyte ratio, and greater antibody titers for Newcastle disease. In the initial period, VaCC birds showed lower BW gain than nonvaccinated birds, but VaCC birds achieved the same performance for the total period. Vaccination against coccidiosis resulted in lower absolute and relative bursa weights and bursa diameters, but also lower lymphocyte bursa depletion or less damage in bursal lymphocytes. Vitamin E had no effect on these parameters. In addition, blood analysis was not affected by vitamin E, but VaCC birds showed lower hematocrit and hemoglobin values and higher leukocyte and lymphocyte values. The 65 mg/kg level of vitamin E positively affected performance and improved the humoral immune response, mainly for immunologically challenged birds.