411 Effect of different feed additives on the caecal microflora of broiler chickens G. Babinszky 1 , G. Csitári 1 , Sz. Tóth 2 ,L. Wágner 2 , L. Pál 2 and K. Dublecz 2* , 1 University of Veszprém, Faculty of Agriculture, Department of Chemistry and Microbiology, 2 University of Veszprém, Faculty of Agriculture, Department of Animal Physiology and Animal Nutrition, H-8360 Keszthely, Deák F. u. 16. Hungary. E-mail: babinszky.g@georgikon.hu Abstract In this work, the effect of different feed additives and an antibiotic growth promoter on the numerical changes of some potentially human pathogen and other bacteria of the caecum of broiler chicks was investigated. Compared to the control diet, without any feed additive treatments increased significantly the number of Lactobacilli and decreased the number of sulphite-reducing Clostridia, Escherichia coli and Campylobacter germs. Clostridium perfringens, Salmonella sp. and Escherichia coli O157:H7 were not detected in any samples. Introduction After June 1999 the majority of antibiotic growth promoters applied in monogastric diets were removed within the EU. These products have been used for many years in the poultry industry and have proved to be an effective way of enhancing animal health status, uniformity and production efficiency (Bedford, 2000). With the restricted use or outright ban of dietary antimicrobial agents, new ways of improving and protecting the health status of farm animals must be explored (Wenk, 2000). One of these opportunities might be using various feed additives of natural origin. The microflora of the digestive tract plays a very important role in farm animals. Among microorganisms, that can be found in the digestive system of broilers, the potential human pathogens like Salmonella and Campylobacter species, Clostridium perfringens and Escherichia coli (including serotype O157:H7) have great importance. Others, like species of Lactobacillus genus, playing a significant role in controlling the pH of the digestive tract and the immune processes of chicks. The aim of this work was to compare the effect of different feed additives on the above mentioned microbe population of the caecum. Materials and Methods 480 Ross 308 broiler chicks were kept in cages. Commercial broiler starter, grower and finisher diets, based on corn and soybean meal were fed ad libitum. In the experiment the following treatments were used: control (K) without feed additive, traetment “A” containing avilamycin (5 mg/kg), “B” essential oils and organic acids, “C” mannose oligosaccharide (MOS), while “D” and “E” different plant extracts. After 42 days 6 animals per treatment were slaughtered and caecal contents collected for analysis of their microbial content. Depending on total amount, 0.32-2.73 g caecal contents were immediately placed into screw-cap tubes, each contained 9 ml of DRCM broth (Differential Reinforced Clostridial Broth; Merck). Determination of total and sulphite-reducing Clostridia: After homogenisation, serial dilutions (10 1 -10 3 ) were prepared from each sample, using DRCM. From all dilutions, plates were poured using SPS agar (Perfringens Selective Agar acc. to Angelotti; Merck) and incubated in anaerobic jars or anaerobic bags. In these circumstances both spores and vegetative forms could germinate. In the course of evaluation, number of sulphite-reducing Clostridia was concluded by counting of black colonies. After this, one plate from each treatment was chosen for further identification, by dint of API 20 A strips (bioMérieux), according to the manufacturer’s recommendations. The