Control of gastrointestinal nematodes in cattle under dry pasture conditions

During the unusually dry and warm summer of the year 2003, the efficacy of a biological (Duddingtonia flagrans) and an anthelmintic control strategy (morantel sustained release trilaminate bolus) against gastrointestinal nematodes (GIN) was tested in comparison with a negative control in a field trial using three groups of 20 first season grazing cattle. The climatic conditions reduced the infection risk on the experimental pastures via direct factors (reduced migration of infective stages onto pasture, increased mortality rate) and indirect ones (reduced stocking rate, supplementary feeding). Under these circumstances neither the chemical nor the biological control strategy was necessary in order to maintain GIN infection at a low level. Largely unaffected by the parasite infections, the calves of the Duddingtonia, bolus and control group had average daily weight gains of 688, 678 and 676 g respectively. As long as D. flagrans was administered, only 25% of the GIN eggs in the coprocultures developed into infective larvae, compared to 83% in the control group, showing the efficacy of D. flagrans. Furthermore, during the final period of the experiment, the infection pressure was approximately 90% lower on the pastures actually grazed by Duddingtonia-treated calves than on the pastures of the control group. In the context with data from various international studies the detection of D. flagrans in a soil sample of Switzerland is suggesting an ubiquitous occurrence of this nematophagous fungus.