Campylobacter infection of broiler chickens in a free-range environment

Abstract

Campylobacter jejuni is the most common cause of bacterial gastroenteritis worldwide, with contaminated chicken meat considered to represent a major source of human infection. Biosecurity measures can reduce C. jejuni shedding rates of housed chickens, but the increasing popularity of free-range and organic meat raises the question of whether the welfare benefits of extensive production are compatible with food safety. The widespread assumption that the free-range environment contaminates extensively reared chickens has not been rigorously tested. A year-long survey of 64 free-range broiler flocks reared on two sites in Oxfordshire, UK, combining high-resolution genotyping with behavioural and environmental observations revealed: (i) no evidence of colonization of succeeding flocks by the C. jejuni genotypes shed by preceding flocks, (ii) a high degree of similarity between C. jejuni genotypes from both farm sites, (iii) no association of ranging behaviour with likelihood of Campylobacter shedding, and (iv) higher genetic differentiation between C. jejuni populations from chickens and wild birds on the same farm than between the chicken samples, human disease isolates from the same region and national samples of C. jejuni from chicken meat.

Fig. 1

Correlation of Campylobacter diversity with (A) percentage of birds ranging and (B) growth rate and hock burn. There was no correlation between Campylobacter diversity and ranging behaviour. Increased diversity of Campylobacter genotypes was positively correlated with decreasing growth rate and improving hock health. A. Diversity = 0.602 + 0.003% birds on range. S = 0.233, R-Sq = 1.3%, R-Sq (adj) = 0.0%. B. Diversity = 1.374 − 0.019 growth rate. S = 0.207, R-Sq = 23.9%, R-Sq (adj) = 22.3%.

Fig. 2

Abundance curve of C. jejuni clonal complexes isolated from wild birds and free-range chickens.