External contamination of broilers by spp. increases from the farm to the slaughterhouse.

1. In this study, classical and molecular microbiological methods for detection and quantification of spp. were used to estimate their prevalence in faecal samples and skin swabs collected from 31 broiler flocks (20 farms) in Portugal, and measure the impact of transport-related factors on the expected rising excretion rates from the farm to the slaughterhouse. 2. Data on husbandry practices and transport conditions were gathered, including time in transit, distance travelled or plant-holding time. 3. A generalised linear mixed model was used to evaluate the significance of a potential post-transport rise in spp. counts and to assess risk determinants. 4. At least one flock tested positive for spp. in 80% of the sampled farms. At the slaughterhouse, spp. were detected in all faecal samples, being the most commonly isolated. 5. A post-transport rise of spp. counts from skin swabs was observed using classical microbiological methods (from a mean of 1.43 to 2.40 log CFU/cm) and molecular techniques (from a mean of 2.64 to 3.31 log genome copies/cm). 6. None of the husbandry practices or transport-related factors were found to be associated with spp. counts. 7. This study highlights the need for more research to better understand the multi-factorial nature of spp., a public health threat that was found to be highly prevalent in a sample of Portuguese poultry farms.