the effect of threonine and vitamin a on immune system in broiler chickens

two independent experiments were conducted with broilers to determine the effect of threonine and vitamin a on immune system. in first experiment, dietary treatments contained 0.8%, 0.87%, 0.94 % and 1.01 % total threonine. in second experiment, diets were as follows: basal diet without vitamin a; basal diet plus 1500 iu/kg vitamin a; basal diet plus 6250 iu/kg vitamin a; basal diet plus 11000 iu/kg vitamin a. fourteen days after feeding the treatments, cutaneous basophil hypersensitivity, cell-mediated immune response, was determined as the increase in toe-web skin thickness after an injection with phytohemagglutinin-p and twenty-two days after feeding the diets, heterophils and lymphocytes were enumerated. humoral immunity was assessed by intravenous injection of 7% sheep red blood cell at 22 days of age. in first experiment, the titers of immunoglobulin for responses were numerically, but not significantly, increased in birds fed diet containing 0.87 % threonine and decreased in 0.94% and 1.01% threonine. cutaneous basophil hypersensitivity was not affected in chicks, whereas there was a tendency for an increase in birds fed a diet containing 0.87 % threonine at 24 h after injection. in second experiment, the titers of immunoglobulin for responses were significantly increased in birds fed diet containing vitamin a. cutaneous basophil hypersensitivity was also increased by addition vitamin a in the diet. the results obtained on the present study indicated that threonine and vitamin a requirements of broiler based on recommendation of national research council are not sufficient to meet the requirement of the new commercial poultry