Page 1 Introduction In modern intensive poultry production, normal flora is slow in colonizing the intestine of newly hatched chicks(Fuller, 1989).Therefore,antibiotics are usedto prevent diseases and improve growth performance. The use of antibiotics in poultry industry led to development of drug-resistant bacteria (Sorum and Sunde, 2001), drug residues in the body of the birds (Burgat, 1999),and imbalance of normal flora (Andremont, 2000).All of the above led to banning of antibiotic use in poultry diets. One alternative of antibiotics is the use of probiotics. Probiotics are live microorganisms which, when administered in adequate amount, confer a health benefit on the host (FAO/WHO, 2002) and have beneficial efects on growth performance (Dizaji et al., 2012). Eforts made to develop commercial probiotics in which organisms such as Lactobacillus and Bifidobacterium species are incorporated. These commercial probiotics may modulate gut microbial composition, leading to improved gut health and improved resistance to pathogenic bacteria (Staton et al., 2001). The objective of the current study was to observe the role of water-solubleprobiotic(ROEMIN W2)on growth performance and in preventing or treating chicks infected with E.coli. American Research Journal of Agriculture (ARJA) ISSN (Online) : 2378-9018 Volume 2016, 12 pages Research Article Open Access www.arjonline.org Probiotic (ROEMIN W2) Improved Growth Performance and Intestinal Histomorphological Structure in Broilers Challenged With E.Coli El-Hamamy M.M 1 , Amina A. Dessouki 1 , Rania.Hamad 1 , Manal M. A. Mahmoud 2* Department of Pathology 1 , Department of Nutrition and Clinical Nutrition 2 , Faculty of veterinary medicine, Suez Canal University, Ismailia , Egypt dr.manalah@gmail.com Abstract: Thecurrent study investigated the role of commercialprobiotic(ROEMIN W2)on growth performance and in preventing or treating chicks challenged with E.coli.Three hundred one day- old mixed Cobb broiler chicks, divided into 5 groups and reared for 42 days. G1was the control group. G2 received probiotic (ROEMIN W2). G3challenged with E.coli. G4challenged with E.coli after receiving of ROEMIN W2. G5challengedfirstly with E.coli then received ROEMIN W2. Body weight gain, feed consumption, and feed conversion ratio calculated for the complete experimental period. Two birds from each replicate were taken and slaughtered (at the 3 rd and 6 th weeks) for determination of carcass weight. Duodenum collected for both histomorphological and scanning electron microscope studies.ROEMIN W2 significantly improved performance in G2andG4 in spite of the E. coli infection compared to control group. G5 had the same FCR and carcass weight as the control group in spite of the E. coli infection. There was a significantly decreased growth performance in the E coli infected non ROEMIN W2 supplemented group, G3 compared to all other treatments. The collected data revealed pronounced intestinal villi improvement in groups treated with probiotic,while infected non- treated group showed decrease length of villi and increase depth of the crypts recorded. Scanning Electron microscope of groups treated with probiotics showed normal length long finger-like projection.Crypt area showed a numerous number of proliferating enterocytes having longer microvilli. Whereas the E. coli infected group showed short distorted duodenal villi with massive destruction and loss. Keywords: Intestine histomorphology,lactic acid bacteria, broilers, growth performance, E.Coli.