Analysis of variations in the microbiota of chickens fed diets supplemented with different feed additives
Conventional rearing of broiler chickens is based on routine supplementation of the feed with anticoccidials which are approved for use against intestinal coccidiosis. A sub-group of anticoccidials, which functions as ionophores, is also effective against some gram-positive bacteria, including Clostridium perfringens. This is an intestinal bacterium associated with growth depression and important gastrointestinal health problems such as necrotic enteritis and the gizzard erosion syndrome. The dual function of ionophores is part of the explanation to their widespread use in broiler feeds. The ionophore narasin has been the predominant anticoccidial used in broiler rearing in the Nordic countries. Research suggests that although narasin is not used in human medicine, its  use in broiler rearing might promote persistence of vancomycin resistant enterococci. This has led to an expressed concern that use of narasin may stimulate occurrence and spread of bacteria resistant to clinically relevant antibiotics. Dissemination of antibiotic resistant bacteria is a world-wide problem, and there is an increasing pressure to reduce the use of antimicrobial agents in animal production. The purpose of this project was to test non-antibiotic feed additives and identify characteristics of the intestinal microbiota in chickens fed diets supplemented with these alternatives to in-feed anticoccidials.The samples originate from four different feeding trials with Ross 308 broiler chickens reared under similar conditions. The chickens were divided into 6 groups, which were fed similar commercial pelleted diets formulated to meet the Ross 308 nutrition specifications with group specific supplements.Trial 1: group 1, narasin; group 2, no additive; group 3, acid product-A; group 4, acid product-B; group 5, acid product-C; group 6, acid product-D.Trial 2: group 1, narasin; group 2, no additive; group 3, acid product-E; group 4, acid product-F, group 5; yeast product-A, group 6; plant/acid product-A.Trial 3: group 1, narasin; group 2, no additive; group 3; yeast product-B + synbiotic-A, group 4; yeast product-B + plant product-A; group 5, yeast product-A + acid product-B; group 6, yeast product-A + acid product-D.Trial 4: group 1, narasin; group 2, no additive