Effect of Feeding Different Protein and Threonine Levels on Immunocompetence of Broiler Chicks. Journal of Animal Science Research. 23:185-199.
This experiment was designed to evaluate the effects of different levels of dietary crude protein and threonine on immunological responses of broiler chicks. A total of 432 one-day-old male broiler chickens were used in a completely randomized design. Dietary treatments consisted of three levels of threonine (100, 110 and 120% of Ross 308 requirement recommendations) and three dietary crude protein concentrations (90, 95 and 100% of Ross 308 requirement specifications) in a 3×3 factorial arrangement of treatments with 4 replicates of 12 birds each. Feeding different levels of crud protein and threonine had no remarkable effect on Newcastle antibody titer (P>0.05). Reduction in dietary crude protein content tended to decrease primary (P=0.16) and secondary (P=0.13) immune responses against sheep red blood cell (SRBC); however, incremental level of threonine up to 110% of recommended values promoted antibody responses against SRBC antigen (P<0.05). Administration of diets with at least 110% of threonine recommendations caused to significant decrease in albumin to globulin (P<0.01) and heterophil to lymphocyte (P<0.05) ratios. These changes were due to the remarkable increase in the proportions of globulins and lymphocytes (P<0.05). The interaction between crud protein and threonine was significant on lymphatic tissues responses (P<0.05) and the highest relative weights of spleen and bursa of fabricius and also the numbers of jejunal lamina propria lymphatic follicles were obtained when the birds fed high-crud protein high-threonine diets. In conclusion, the present results indicated that although decrease in dietary crude protein content to 90% of recommended values reduced the humoral immune responses and bursa of fabricius relative weight, fortification of diets with threonine up to 110% of Ross 308 recommended values could improve the humoral immune responses and also the proportions of blood globulins and lymphocytes in broiler chicks.