Ileal and caecal microbial populations in broilers given specific essential oil blends and probiotics in two consecutive grow-outs Edgar O. Oviedo-Rondo ´n a* , Michael E. Hume b , Nei A. Barbosa a,c , Nilva K. Sakomura c , Gilbert Weber d and Johnathan W. Wilson e a Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27695-7608, USA b USDA, ARS SPARC, FFSRU, College Station, Texas 77845, USA c Universidade Estadual Paulista, UNESP, FMVZ, Jaboticabal, Brazil d DSM Nutritional Products Ltd. Kaiseraugst, Switzerland e DSM Nutritional Products, Inc., Parsippany, New Jersey 07054, USA *Email: edgar_oviedo@ncsu.edu ABSTRACT Specific essential oil (EO) blends and probiotics used as feed additives have been shown to promote healthy digestive microbials resulting in improved poultry production. Two consecutive experiments were conducted with broilers fed corn-soybean meal diets to determine comparative effects of feed additives on ileal and caecal microbial populations (MP). Ross 708 broilers were placed in 84 pens with previously used litter and treatments maintained in the same pens for both experiments. Eight treatment groups were fed diets containing: Bacitracin methylene disalicylate (BMD) as positive control (PC); no additives as negative control (NC); three probiotics: BC-30; BioPlus 2B (B2B); and Calsporin; and the essential oil blends Crina Poultry Plus (CPP) at 300 or 150 ppm in the first experiment; and CPP at 300 ppm and Crina Poultry AF at 100 ppm in experiment 2. Starter and grower diets contained the ionophore (Coban). Ileal and caecal samples were collected at 43 days of age from male broilers. The DNA of microbial populations was isolated from digesta samples and analysed by denaturing gradient gel electrophoresis to generate percentage similarity coefficients (%SC) from band pattern dendrograms. Differences were observed in ileal and caecal populations depending on treatment, respectively, and especially between experiments. Broilers fed diets with probiotics had very similar MP. The EO CPP at 300 ppm resulted in ileal MP similar to those observed in chickens fed probiotics. We concluded that antibiotic treatment affected ileal, but no caecal MP. More pronounced changes in ileal and caecal MP were seen in broilers at 43 days of age following probiotic and essential oil treatments. Keywords: essential oils, probiotics, microbial ecology, built-up litter, denaturing gradient gel electrophoresis 1. INTRODUCTION Digestive microbial populations (MP) affect broiler performance and health (Apajalahti and Bedford, 1999; Dibner et al., 2008). These effects in the host may be due primarily to nutrient availability, complex interactions among MP that influence the intestinal environment, and responses of the host immune system against pathogenic and non-pathogenic anti- gens (Cebra, 1999; Kelly and Conway, 2005; Dibner et al., 2008). Generally, microflora develop commensal ecosystems with benefits for both microbes and the broiler hosts. However, many factors can cause succession and modification of MP profiles. The succession of MP has been observed in association with broiler age (Lu et al., 2003), or after changes in dietary levels of specific nutrients, such as fat (Knarreborg et al., 2002), protein (Parker et al., 2007), calcium and zinc (Hume et al., 2003), feed withdrawal (Thompson et al., 2008), and changes in pH of the diet (Dibner and Richards, 2004). In general, the strongest determinant of gut MP profiles is the host’s diet (Apajalahti et al., 2001). Dietary factors such as nutrient composition, physical traits, feed processing, and feed additives play signifi- cant roles in the dynamics of gut microflora (Apajalahti et al., 2001; Guo et al., 2004; Hume et al., 2003, 2006; Oviedo-Rondo ´n et al., 2006; AVIAN BIOLOGY RESEARCH 3 (4), 2010 157 – 169 www.avaianbiologyresearch.co.uk doi: 10.3184/175815511X12919853724050 —————— Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation nor endorsement by North Carolina State University or the US Department of Agriculture.