Farm-level risk factors for Fasciola hepatica infection in Danish dairy cattle

Summary

Recent studies suggest that liver fluke (Fasciola hepatica) infections in cattle have increased in Denmark in recent years. This study aimed to identify potential farm level risk factors for liver fluke infection in Danish dairy farms using two different diagnostic methods.
Based on liver condemnation data of all individual cattle slaughtered in Denmark, 145 and 77 farms were selected as cases and matched controls. The selection criteria were; 1) minimum 50 animals were slaughtered in 2013, 2) minimum three cases of liver condemnation due to liver flukes in 2013 (case) / no history of liver condemnation due to liver flukes for the last three years (control), and 3) control farms were located within 10 km from the case farms. Bulk tank milk (BTM) samples from the farms were analysed using enzyme-linked immunosorbent assay (ELISA), and telephone interviews were used to obtain information on the type of production, the farmers’ knowledge about liver fluke infection, grazing pattern, anthelmintic treatments and management routines.
Preliminary results based on 132 case and 64 control farms indicate that grazing was significantly associated with liver fluke infection (p=0.006). However, in 12 case herds, grazing was not applied (all-in systems), suggesting indoor rearing does not completely prevent liver fluke infections, although misdiagnosis or incorrect registration at slaughter is possible. The percentage of farms allowing heifers to graze on wet areas was significantly higher in case than control farms (p<0.001). Using grazing for heifers and drinking from natural waterways were associated with liver fluke infections (p=0.07 and p=0.01). Approximately 30% of case farms tried actively to avoid infection by anthelmintic treatment or preventive management measures. The prevalences of liver flukes estimated by BTM ELISA were 75% and 12.5% for case and control groups, respectively. The negative ELISA results in some of the case herds may be due to their low in-herd prevalence, but it is still under investigation.
Based on the risk analysis, we expect grazing management can be improved on many infected farms as part of the control of liver fluke. The substantial discrepancy between different diagnostic methods should be taken into account for future studies.