Influence of production system on the rate of onset of Campylobacter colonization in chicken flocks reared extensively in the United Kingdom

Abstract

1. Because thermophilic Campylobacter spp. are common in chicken flocks reared extensively, cross-sectional and longitudinal studies were carried out on organic and free-range farms to determine the onset of colonisation (lag phase) and likely sources of flock infection.

2. For 14 organic and 14 free range flocks, there was a difference in lag phases, with the former being colonized at a mean of 14·1 d in comparison with 31·6 d for the latter. Whereas most free-range flocks became colonized when released on to pasture, those reared organically were usually colonized at the housed brooding stage.

3. Further study of organic flocks on three farms over 7 successive crop cycles confirmed that colonisation was strongly influenced by the prevailing husbandry conditions and was not a consequence of the length of the rearing period.

4. Molecular epidemiological investigations on a farm showing the shortest lag phase, using PFGE typing with two different restriction enzymes (SmaI and KpnI) and flaA SVR sequence typing, revealed that potential sources of colonisation for organic chickens were already present on the farm at the time of chick placement. Such sources included the ante area of the brooding house, surrounding pasture and other livestock being kept on the farm.

5. Overall, the study demonstrated that, under UK conditions, the prevalence of colonisation was greater in extensive flocks (95–100%) than it was for conventional broilers (55%), similar to the situation in other countries, but all three management systems showed comparable levels of caecal carriage in positive birds (log₁₀/g 6·2–6·7).

Acknowledgements

The authors gratefully acknowledge the assistance given by farmers, managers and technical staff of the poultry companies concerned. Drs Fran Colles and Noel McCarthy of the Peter Medawar Building for Pathogen Research and department of Zoology, University of Oxford, are thanked for provision of MLST typing data together with Meenaxi Sharma and Angela Tatton for their excellent technical assistance. This study was part of a project funded by the UK Department for Environment, Food and Rural Affairs.