The potential of Duddingtonia flagrans to control gastrointestinal nematode parasites of sheep under field conditions in New Zealand

The development of nematode resistance to anthelmintics and increasing consumer demand for chemical free products mean alternative methods are required for gastrointestinal parasite control in livestock. Overseas trials have demonstrated that the nematophagous fungus D. flagrans is able to significantly reduce infective larval numbers on pasture and subsequently reduce the level of infection in animals grazing treated pasture. The purpose of this study was to evaluate the potential of three New Zealand D. flagrans isolates to control infective stage larvae on pasture under New Zealand climatic conditions. Pasture plot studies confirmed that all three isolates were able to passage the sheep gastrointestinal tract and significantly reduce the number of Trichostrongylus colubriformis larvae developing in faeces deposited in the field during autumn by 50%, 93% and 93%. A replicated field trial with grazing animals showed a lower small intestinal worm burden in tracer animals on treated pastures compared with untreated pastures, however this was not significant (p=0.467) due to the large amount of variation within groups of tracer animals. Significant (p=0.037) reductions of between 66% and 86% in the abomasal worm burden of tracer animals grazing treated pasture were recorded. The number of infective larvae recovered from pasture samples were reduced on 2 out of 3 treatment paddocks. The third block was very dry, and although there were no differences in pasture larval counts, tracer animals on the treated paddock had a lower worm burden. A trial to establish the effect of seasonal climatic differences using pasture plots trial under spring conditions and a programmable incubator for simulated winter temperature conditions found a reduction in the number of T. colubriformis infective larvae recovered when cultures were treated with fungus, however, variation between samples meant there was no statistically significant difference. The low initial concentration of parasite eggs may have contributed to the poor performance of fungi in this trial when compared to the first set of plot trials in autumn and future comparative efficacy trials must be standardised for faecal egg count. This study has demonstrated that New Zealand D. flagrans isolates appear to have a similar level of efficacy under local conditions as those tested overseas and show potential as biological control agents. A number of issues require investigation prior to any commercial release of D. flagrans and these are discussed.