Farm-level risk factors for Fasciola hepatica infection in Danish dairy cattle as evaluated by two diagnostic methods

Summary

Background: The prevalence of bovine fasciolosis in Denmark is increasing but appropriate guidelines for control
are currently lacking. In order to help develop a control strategy for liver fluke, a risk factor study of farm management
factors was conducted and the utility of bulk tank milk (BTM ELISA) as a tool for diagnosis in Danish dairy cattle farms
was assessed.
Methods: This case-control study aimed to identify farm-level risk factors for fasciolosis in Danish dairy farms (> 50
animals slaughtered in 2013) using two diagnostic methods: recordings of liver condemnation at slaughter, and
farm-level Fasciola hepatica antibody levels in BTM. A case farm was defined as having a minimum of 3 incidents
of liver condemnation due to liver fluke at slaughter (in any age group) during 2013, and control farms were located
within 10 km of at least one case farm and had no history of liver condemnation due to liver fluke during 2011–2013.
The selected farmers were interviewed over telephone about grazing and control practices, and BTM from these farms
was collected and analysed by ELISA in 2014. The final complete dataset consisting of 131 case and 63 control farms
was analysed using logistic regression.
Results: Heifers grazing on wet pastures, dry cows grazing on wet pastures, herd size, breed and concurrent beef
cattle production were identified as risk factors associated with being classified as a case farm. With the categorised
BTM ELISA result as the response variable, heifers grazing on wet pastures, dry cows grazing on wet pastures, and
purchase of cows were identified as risk factors. Within the case and control groups, 74.8 and 12.7% of farms were
positive for fasciolosis on BTM ELISA, respectively. The differences are likely to be related to the detection limit of
the farm-level prevalence by the BTM ELISA test, time span between slaughter data and BTM, and the relatively
low sensitivity of liver inspection at slaughter.
Conclusions: Control of bovine fasciolosis in Denmark should target heifers and dry cows through grazing management
and appropriate anthelmintic treatment, and BTM ELISA can be a useful diagnostic tool for fasciolosis in Danish
dairy farms.