The present study was carried out to evaluate the effects of biological (Bacillus subtilis and Enterococcus faecium) supplementation on productive performance, physiological and immunological response of Hy-line layer chicks. Total of 300 one-day old of Hy-line layer chicks, were randomly divided into three groups. The first group was fed a basal diet and served as a control. While the second and third groups were fed the basal diet that supplemented with the probiotic mixture at the rate of 1 and 2 gm/kg of diet, respectively, until 10 weeks of age. Results indicated that treated groups with helpful bacteria (B. subtilis and E. faecium) showed significant effect on final body weight gain, feed conversion ratio and higher antibody levels against Newcastle disease virus as compared to the control one. Moreover, significant increase was recorded in the relative weight of carcass, liver, heart, kidney, proventiculus, small intestine, thymus, spleen, bursa of Fabricius and small intestine length (cm) in all supplemented groups as compared to the control group. On the other hand, there were no significant effects on serum total protein, albumin, globulin and creatinine concentrations, while, serum ALP, ALT, AST activities, uric acid, triglycerides and cholesterol concentrations in all treated groups were significantly lower than in control group. Furthermore, serum glucose, calcium, phosphorus concentrations and triiodothyronine hormone level were significantly higher in treated groups than the control. Red and white blood cell counts, hemoglobin level and hematocrit values were significantly increased in all treated groups as compared to control group. In conclusion, biological (B. subtilis and E. faecium) supplementation can be used as one of important additive for enhancing the productive efficiency, and immunity of growing Hy-line chicks.
