The present invention generally concerns the biological control of gastrointestinal nematode infections in grazing mammals. The invention provides Duddingtonia flagrans strains that are useful for reducing the parasitic nematode populations in feces of the mammals deposited on grassland. The invention also concerns a method for selecting D. flagrans strains exhibiting improved nematode capturing properties. In some aspects, the invention concerns a feed additive formulation comprising a D. flagrans strain for oral administration to grazing mammals for biologically reducing the spread of infective nematodes on grassland.
