This study was conducted to evaluate the effects of dietary supplementation of organic acids (AH) (lactic, formic and citric), probiotic (MVS) (Lactobacillus, Saccharomyces cerevisiae, and Aspergillus), and a combination of organic acids and probiotic (AHM) on the performances, feed conversion ratio and fecal E.coli excretion of commercial Cobb broiler chickens. Total 320 Cobb 500 chickens at 1 day of age were divided into 4 groups of 4 treatments. The control (ĐC) was basal diet without any organic acid or probiotic added in the diet, other treatments were AH (2%), MVS (2%) and combination of AH (1%) +MVS (1%) (AHM) supplementations by the week. Average daily gain (ADG) from birds fed with 3 supplemented diets with AH (53,74 g/day), MVS (55,91 g/day ) and AHM (56,1 g/day) were higher than that from ĐC (52,02 g/day).Feed intake was non significant differences between 4 treatments. Howevers, there were significantly lower feed conversion ratio (FCR) in AHM chickens (1,67 kg feed/kg gain) than the others treatments especially ĐC (1,77 kg feed/kg gain). Moreover, E.coli content in the chickens feces was highest in the chickens fed ĐC diet (1,91x10⁶CFU/g) then AH diet (1,63 x10⁶CFU/g) and lowest in the AHM chickens (1,52 10⁶CFU/g). The morbility and mortality of chickens fed AHM was lowest (18,9% and 4,25%) in comparision with control diet (28,9% and 6,75%). In conclusion, it should be better in growing performance of broiler Cobb chickens when a combination of organic acids and probiotic was supplemented to diet by the week insteat of using antibiotic in broiler chickens diet.

Keywords: Broiler, Cobb, E.coli, Probiotic, Organic acids