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Title: An individual bird challenge model is superior to group challenge for trials designed to determine colonization dose

Author
item Line, John
item Hiett, Kelli
item CONLAN, A.J. - U OF CAMBRIDGE, UK

Submitted to: Poultry Science
Publication Type: Proceedings
Publication Acceptance Date: 7/22/2008
Publication Date: 9/23/2008
Citation: Line, J.E., Hiett, K.L., Conlan, A.K. 2008. An individual bird challenge model is superior to group challenge for trials designed to determine colonization dose. Poultry Science.

Interpretive Summary:

Technical Abstract: Studies investigating the impact of probiotic intervention technologies can be confounded by coprophagic activity (a normal activity among broiler chickens) if such activity results in the re-exposure of birds from which the pathogen was previously eliminated. The purpose of this study was to compare an individually-housed chick model (where bird-to-bird coprophagia was prevented) to a group-housed chick model (where bird-to-bird coprophagia was allowed) for determining estimates of the number of Campylobacter jejuni RM1221 necessary to colonize 50% of broiler chicks inoculated (colonization dose 50% or CD50). Campylobacter jejuni RM1221 was orally administered in measured doses to newly hatched chicks. The chicks were housed either individually in cages designed to minimize coprophagous activity, or in isolation units containing groups of birds where coprophagia was allowed. The birds were sacrificed and analyzed for Campylobacter in the ceca on day 7 post-inoculation. The CD50 was calculated and results from the two models were compared. Elimination of transmission of Campylobacter, through coprophagia or other means, led to a more clear determination of the estimated CD50 of about 524 CFU C. jejuni RM1221 as demonstrated in the individually-housed chick model. Baysian inference based on Beta-Poisson statistical modeling procedures were found to be superior to standard single-hit dose response modeling for estimation of the CD50. This study demonstrated that the individual bird challenge model is superior to the group challenge model for trials designed to determine colonization dose.