The Effect of Different Levels of Crude Protein and Threonine on Performance and Immune system of Broiler Chickens during Starter and Grower Periods

This experiment was conducted to evaluate the effect of different levels of crude protein and threonine on performance, carcass characteristics and immune system of broiler chickens during starter (7-24) and grower (25-42) periods. A total of 288 male broiler chicks of Ross 308 strain were used in a completely randomized design with factorial arrangement (2×4) with three replicates in each treatment. Experimental diets were included two levels of protein (Ross 308 guideline recommendation and 5% lower than the recommendation) and four levels of threonine (90, 100, 110, 120 of NRC recommendation). At starter period, threonine levels had a significant effect on feed conversion ratio (P