Abstract
<title>Abstract</title> <p> Background The trematode parasites <italic>Fasciola hepatica</italic> and <italic>Calicophoron daubneyi</italic> infect grazing livestock following ingestion of metacercariae encysted on herbage. However, the influence of forage species on metacercariae encystment is poorly understood. The aim of this study was to determine whether the encystment of <italic>F. hepatica</italic> and <italic>C. daubneyi</italic> differed among common forage species. Methods Infected <italic>Galba truncatula</italic> snails were stimulated to shed cercariae in the presence of forage material. Single-forage assays were conducted for <italic>F. hepatica</italic> and <italic>C. daubneyi</italic> using eight and three forage species, respectively, and a mixed-forage assay compared Italian ryegrass, Timothy and Cocksfoot for <italic>F. hepatica</italic> . Metacercarial recovery from plant and non-plant locations was recorded with encystment rates analysed using beta-binomial models. Results Encystment rates differed among forage species with <italic>F. hepatica</italic> encystment rates lower on Timothy (OR = 0.438, <italic>p</italic> = 0.036) and Yorkshire Fog (OR = 0.106, <italic>p</italic> < 0.001) compared to Italian ryegrass. In the mixed-forage assay, <italic>F. hepatica</italic> encystment was also lower on Cocksfoot (OR = 0.519, <italic>p</italic> = 0.040) and Timothy (OR = 0.453, <italic>p</italic> = 0.015) than on Italian ryegrass. Leaf surface analysis indicated lower-surface bias for <italic>F. hepatica</italic> metacercariae on Ryegrass and Yorkshire Fog ( <italic>p</italic> < 0.05). In contrast, <italic>C. daubneyi</italic> encystment was higher on Plantain (OR = 38.305, <italic>p</italic> < 0.001) and Yorkshire Fog (OR = 26.862, <italic>p</italic> = 0.001) than on Italian ryegrass. Conclusions Forage species influenced the encystment of <italic>F. hepatica</italic> and <italic>C. daubneyi</italic> metacercariae, with contrasting patterns between fluke species. These findings suggest that plant-parasite interactions during the free-living metacercarial stage may influence the spatial distribution of infective stages on pasture. Semi-natural and field-based studies are needed to determine whether these differences affect transmission risk under grazing conditions. </p>