Prevalence and magnitude of helminth infections in organic laying hens (Gallus gallus domesticus) across Europe.

Helminths are associated with health- and welfare problems in organic laying hens. The present observational cross-sectional study therefore aimed to estimate the prevalence and worm burdens of intestinal helminths in organic flocks of laying hens in 8 European countries, and to identify management factors that might be associated with helminth infections, with emphasis on Ascaridia galli. Data on flock-level management factors (e.g. nutritional factors, litter quality, housing system, opening- and closing hours of popholes, pasture rotation and provision of occupational materials) were collected during a farm visit when the hens were on average 62 weeks old. Worm counts were performed for 892 hens from 55 flocks and the number of ascarid (presumably primarily A. galli) eggs per g faeces (EPG) for 881 hens from 54 flocks. The association between parasitological parameters (prevalence, worm burden and EPG) and the management factors were analysed by multivariate models. Results showed that A. galli was highly prevalent across Europe with an overall mean prevalence of 69.5% and mean worm burden of 10 worms per hen. The overall mean prevalence and worm burden for Heterakis spp. were 29.0% and 16 worms per hen, respectively, with a large variation between countries. On average, the hens excreted 576 ascarid EPG. The mean prevalence of Raillietina spp. was 13.6%. A positive correlation was found between mean A. galli worm burden and ascarid EPG. Of the analysed management factors, only pasture access time had a significant negative association with A. galli worm burden which was in contrast to the general belief that outdoor access may increase the risk of helminth infections in production animals. In conclusion, the complexity of on-farm transmission dynamics is thus a challenge when evaluating the relative importance of management factors in relation to helminth infections.