This experiment was conducted to evaluate the effect of two types of probiotic and antibiotic virginiamycin on performance, carcass characteristics, gastrointestinal microbial population and Serum biochemical values of broiler chickens. Based on a completely randomized design, three hundred day old Ross 308 broilers were allotted into 4 treatments with 5 replicate pens per treatment and 15 broilers in each pen for 42 days. Dietary treatments were (1) an antibiotic-free corn-soybean meal mash basal diet (control), (2) control + 200 g/ton of virginiamycin, (3) control + 1500 g/ton of fermented probiotic produced and isolated from fermented poultry slaughterhouse wast, and (4) control + 1000 g/ton of commercial probiotic (BioPlus-2B®). The results indicated that the use of antibiotic improved body weight gain (BWG) (7.2 and 8.6 % respectively) and feed conversion ratio (FCR) (3.24 %) as compared to control and commercial probiotic treatments (P<0.05). Also, the birds under virginiamycin treatment had higher feed intake (FI) than those treated with commercial probiotic. The use of fermented probiotic relatively improved BWG (3.28 %) and FCR (1.0 %) as compared to control. Efficiency of dressed carcase, breast, thigh and internal organs including liver, heart, bursa of fabricius and spleen were not affected by these experimental treatments (P˃0.05). Adding commercial probiotic to the basal diet increased the relative weight of gizzard than fermented probiotic and reduced the relative weight of abdominal fat pad than virginiamycin treatment (P<0.05). Both of these probiotics increased total bacterial population in crop when compared with virginiamycin (P<0.05). The use of fermented probiotic significantly increased the lactic acid bacteria population in crop than antibiotic treatment. Fermented probiotic supplementation significantly lowered the pH of ileum than those control and antibiotic treatments. Antibiotic virginiamycin and fermented probiotic were effective to reduce ileum coliforms population when compared to control and commercial probiotic treatments (P<0.05). The use of commercial probiotic reduced the blood concentration of cholesterol when compared to control birds (P<0.05). The serum concentration of triglyceride and very low density lipoprotein (VLDL) in birds under fermented probiotic significantly was lower compared to antibiotic treatment. None of these fed additives had significant effect on other Serum biochemical parameters including glucose, high density lipoprotein (HDL), low density lipoprotein (LDL), total protein, albumin and globulin. According to the present study, fermented probiotic has been found to have a positive effect especially on body weight of broilers. The use of fermented probiotic is therefore recommended to effectively replace conventional antibiotics.

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