The liver fluke Fasciola hepatica is a trematode parasite with a worldwide distribution and is the cause
of important production losses in the dairy industry. The aim of this observational study was to assess
the prevalence of exposure to F. hepatica in a group of high yielding dairy herds, to determine the risk
factors and investigate their associations with production and fertility parameters. Bulk milk tank samples
from 606 herds that supply a single retailer with liquid milk were tested with an antibody ELISA for F.
hepatica. Multivariable linear regression was used to investigate the effect of farm management and
environmental risk factors on F. hepatica exposure. Higher rainfall, grazing boggy pasture, presence of
beef cattle on farm, access to a stream or pond and smaller herd size were associated with an increased
risk of exposure. Univariable regression was used to look for associations between fluke exposure and
production-related variables including milk yield, composition, somatic cell count and calving index.
Although causation cannot be assumed, a significant (p < 0.001) negative association was seen between
F. hepatica exposure and estimated milk yield at the herd level, representing a 15% decrease in yield for
an increase in F. hepatica exposure from the 25th to the 75th percentile. This remained significant when
fertility, farm management and environmental factors were controlled for. No associations were found
between F. hepatica exposure and any of the other production, disease or fertility variables.