Foraging for a fluke: Plant DNA metabarcoding reveals dietary signatures associated with liver fluke exposure in grazing lambs.

Understanding within-flock variation in parasite exposure can underpin more targeted and sustainable control strategies. However, for Fasciola hepatica, the extent and drivers of such variation remain poorly understood, despite transmission requiring an intermediate host snail and therefore being inherently heterogeneous within grazing environments. This study investigated whether faecal plant DNA metabarcoding could identify dietary signatures associated with recent F. hepatica exposure in first-season grazing lambs. A total of 157 lambs from two commercial sheep farms in Wales, grazing land containing G. truncatula populations were screened using serum antibody ELISA, coproantigen ELISA and faecal egg counts. Nineteen lambs (12.1%) were seropositive, while coproantigen and pooled faecal egg counts were negative, consistent with recent exposure. Faecal samples from 17 seropositive and 19 seronegative lambs were analysed using complementary chloroplast trnL and rbcL metabarcoding markers via MinIon sequencing. Plant assemblage composition was strongly structured by farm, with F. hepatica status significantly associated with trnL community composition at both genus (R² = 0.059, p = 0.049) and family (R² = 0.073, p = 0.035) levels. Indicator taxon analysis identified Lolium, Ranunculus and Trifolium among taxa associated with F. hepatica positive lambs, whereas Corylus, Carpinus and Mentha were associated with F. hepatica negative lambs. These findings suggest that recent F. hepatica exposure is associated with distinct dietary signatures and that individual variation in forage and habitat use may contribute to heterogeneous exposure within flocks.