The effects of supplementing diet of growing lambs with microbial feed additive mixture (direct-fed microbial; DFM) based on Saccharomyces cerevisiae, lactic acid bacteria and exogenous enzymes on feed intake, nutrient digestibility, nitrogen (N) utilization, ruminal fermentation, blood chemistry and growth performance were studied. The study was a completely randomized design with 12 growing Barki lambs divided into two groups of six lambs per treatment. Lambs were offered a control diet of peanut hay and concentrates (1:1 dry matter (DM) basis) or the control diet supplemented with DFM at 0.5 g/day (Bactozyme treatment) for 16 weeks. There was no effect on feed efficiency but Bactozyme lambs had increased (p = 0.009) feed intake, average daily gain (p = 0.042) and final body weight (p = 0.047). Bactozyme treatment had greater neutral detergent fiber (p = 0.020) and acid detergent fiber (p = 0.034) digestibility compared with the control treatment. Metabolism experiment showed that the feed additive mixture increased (p<0.05) N intake and N retention. Bactozyme treatment had greater blood total protein (p = 0.027), and globulin (p = 0.025) concentrations compared with the control treatment. It is concluded that supplementing growing Barki lambs with DFM at 0.5 g daily enhanced final body weight gain and fiber digestion without affecting feed efficiency.