| Summary: | Cattle are an established reservoir of the foodborne bacterial pathogen <i>Campylobacter jejuni</i>. Our six-month study aimed to evaluate sources and pathways governing long-term presence of <i>C. jejuni</i> in a pasture-based dairy herd. <i>C. jejuni</i> was detected in all sample types (soil, pasture, stock drinking water, bird, rodents and cow faeces). It was persistently detected from cow (54%; 49/90 samples) and bird (36%; 77/211) faeces. Genetic comparison of 252 <i>C. jejuni</i> isolates identified 30 Multi-Locus Sequence Types (ST). ST-61 and ST-42 were persistent in the herd and accounted for 43% of the cow isolates. They were also detected on pasture collected from fields both recently and not recently grazed, indicating that grazed pasture is an important pathway and reservoir for horizontal transmission among cows. ST-61 accounted for 9% of the bird isolates and was detected at four of the six sampling events, suggesting that bird populations might contribute to the cycling of ruminant-adapted genotypes on-farm. Overall, the results indicated that management of grazed pasture and supplementary feed contaminated by bird droppings could be targeted to effectively reduce transmission of <i>C. jejuni</i> to dairy herds, the farm environment and ultimately to humans.
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