This experiment was conducted to investigate the effects of different levels of yeast single cell protein on functional traits, blood biochemical parameters, immune titer, population of caecum bacteria and morphology of broilers intestine in the form of a completely randomized design with 6 treatments, each treatment 5 replication and each replication 15 one-day pieces of broilers. The experimental treatments were included in: 1) control group; 2) the receiving group of single cell protein 0.03 percent; 3) the receiving group of single cell protein 0.05 percent; 4) the receiving group of single cell protein 0.07 percent; 5) the receiving group of protein Single cell 0.09 percent, 6) the receiving group of single cell protein 0.1 percent. The results of the experiment showed that the treatments receiving different levels of yeast single cell protein showed a higher weight gain compared to feed intake control treatment and as a result, their conversion factor was less than that of control treatment. The use of different levels of single cell protein improved blood biochemical parameters and increased immune titer against Newcastle and influenza disease compared to control treatment. In this study, it was observed decreasing population of Salmonella and E. coli, as well as the increasing population of caecum lactobacillus in chicks receiving single cell protein in comparison to control. Also, it was observed increasing Willy's height, decreasing crypt depth, and reducing the number of goblet cells in chicks receiving different level of single cell protein.
