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Cecal enteritis due to Brachyspira infections tends to be chronic in laying hens. Limited availability of antimicrobial drugs for use in laying hens emphasizes the need for alternative control measures. A broth microdilution method was used to determine the antimicrobial susceptibility of 20 Brachyspira intermedia field isolates from laying hen flocks to components of essential oils (EO). Minimal inhibitory concentration (MIC) distributions, obtained for 8 EO components, were all monomodal. Cinnamaldehyde had the lowest MIC values (40 to 80 mg/L), followed by nerolidol, capsaicin, carvacrol, and thymol (80 to 320 mg/L), eugenol (160 to 640 mg/L), and linalool (320 to 1,280 mg/L). The MIC ranges of piperine were mostly above the test range of 1,280 mg/L. In an in vivo experiment, coated trans-cinnamaldehyde was supplemented to the feed of rearing pullets. A completely randomized experimental design with 4 treatments and 3 replicates each (replicate = group of seven 1-d-old laying hen chickens) was applied. The negative and positive controls received a conventional feed during the whole trial. The positive controls were orally inoculated on 3 consecutive days (d 22, 23, and 24) with 1 mL of 1.0 × 10(8) cfu/mL of a B. intermedia field isolate. Two treatment groups (preventive and curative), identically inoculated, received the coated trans-cinnamaldehyde-supplemented feed (500 mg/kg of trans-cinnamaldehyde), the preventive group from d 1, the curative from d 25. On d 32, ceca were collected for bacteriologic Brachyspira enumeration. The mean enumeration of Brachyspira cells was decreased (P < 0.05) in the curative treated group versus the positive control group. The in vitro results of the present study demonstrate the potential of EO components as antimicrobials against poultry Brachyspira isolates, including isolates with acquired resistance for classic antimicrobial drugs. Reduction of Brachyspira colonization in young pullets was obtained, in a curative way, in an in vivo study using feed supplemented with coated trans-cinnamaldehyde. Further studies are necessary to investigate the mode of action of the coated trans-cinnamaldehyde in reducing Brachyspira colonization of the ceca.
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