Vitamin E and immune responses of broiler pureline chickens.

Immunological responses of cockerels fed diets containing either 10 or 300 mg/kg of vitamin E were measured in three commercial broiler nuclear lines designated as A, B, and C. All cockerels were fed the 10 mg/kg diet to 91 d of age, at which time half were continued on that diet and the other half were fed a diet supplemented to contain 300 mg/kg of vitamin E. Sixteen days after feeding the diets, cutaneous basophil hypersensitivity (CBH), which is an in vivo, cell-mediated immune response, was determined as the increase in toe-web skin thickness 24 h after an injection with phytohemagglutinin-P (PHA-P). Twenty-two days after feeding the diets, heterophils and lymphocytes were enumerated. At this time cockerels were also inoculated intravenously with 0.1 mL of 0.25% SRBC. The injection with SRBC was repeated 27 d later. Six and 20 d after each injection, antibody titers were determined. Mercaptoethanol-resistant (IgG) and mercaptoethanol-sensitive (IgM) antibodies were also measured in the secondary titers. The ratio of heterophils to lymphocytes increased, and CBH response was depressed by feeding the higher vitamin E diet. For cockerels of Lines A and B, the higher level of vitamin E maintained primary and secondary SRBC antibody levels, whereas for Line C, levels were depressed. The effect of the higher vitamin E diet on IgG and IgM was also stock-dependent. The enhanced heterophil:lymphocyte ratio from feeding vitamin E suggests an improved phagocytic ability of the immune system. Relative asymmetries for toe-web skin thickness and shank length were similar for the three lines.