To compensate for possible decreases in animal production due to restrictions on the use of antibiotics as growth promoters, several non-antibiotic alternatives have been investigated. Organic acid supplementation (OAS) of feed or water has shown some promising results for affecting intestinal microbiota and reducing pathogenic bacteria in the gastrointestinal (GI) tract. However, few studies have explored the effects of OAS on microbial communities using objective molecular-based techniques. The aim of the present study was to characterize via 16S rRNA gene-based approaches responses of the intestinal microbiota after OAS in chicks. Newborn chicks were randomly divided in four treatments: (a) control (no antibiotic, no OAS); (b) antibiotic administration (bacitracin MD); (c) organic acid blend dl-2-hydroxy-4(methylthio) butanoic acid [HMTBA]; lactic, and phosphoric acid (HLP); and (d) organic acid blend HMTBA, formic, and propionic acid (HFP). Ileal contents and mucosal scrapings from 7 chicks/treatment/day were taken at 15, 22, and 29 days of age, and genomic DNA was isolated for the molecular analysis of the intestinal microbiota. The data demonstrate that HFP blend treatment for 29 consecutive days affected ileal microbial populations as indicated by community fingerprinting analysis (16S rRNA PCR-DGGE). In parallel, total bacterial and lactobacilli populations were increased by the HFP blend treatment as demonstrated by targeted qPCR analysis of 16S rRNA VSports手机版. In summary, the present data demonstrate that OAS, HFP blend treatment in particular, shifts intestinal microbiota, generates more homogenous and distinct populations, and increases Lactobacillus spp. colonization of the chick ileum. .