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Improvements in nematophagous fungi to control gastro-intestinal parasites : this thesis is presented in partial fulfilment of the requirements for the degree of Master of Veterinary Studies in Veterinary Parasitology, Massey University, Palmerston North, New Zealand
Gastro-intestinal parasites are a major cause of production loss in New Zealand livestock, and the continuing development of anthelmintic-resistant strains represents a significant threat to the future New Zealand agricultural economy. This has led to an increased interest in alternative (non-chemotherapeutic) controls, including potential application of the nematode-trapping fungi Duddingtonia flagrans and Arthrobotrys oligospora. These species are capable of reducing the number of free-living stages of trichostrongylid nematodes developing in faeces, following oral administration or the addition of fungal material to faeces. However, high spore mortality through the gastro-intestinal tract currently limits the development of a commercial product, even for the robust chlamydospores of D. flagrans. The potential to reduce spore mortality by applying a protective coating to the spores was investigated, and an in vitro rumen simulation bioassay was used to quantitatively evaluate and compare the survival of D. flagrans and A. oligospora spores in a series of experiments. These experiments revealed that unprotected D. flagrans chlamydospores were superior to A. oligospora conidia in their ability to withstand the debilitating effects of rumen fluid. However, the survival of A. oligospora was improved by integration into a biopolymer formulation. Dried D. flagrans chlamydospores were more resistant to a simulated rumen environment than freshly harvested chlamydospores, and exposure to water as an incubation medium was less detrimental than rumen fluid to the survival of both fresh and dried D. flagrans chlamydospores. The application of a stearic acid coating to dried D. flagrans chlamydospores failed to improve spore survival in either a simulated rumen environment, or efficacy during subsequent in vivo testing. However, as the application of a biopolymer formulation successfully improved the survival of A. oligospora conidia, it is likely that similar formulations may be successfully applied to other fungal species. These results highlight the potential for development of formulations containing multiple species of nematophagous fungi, including the application of fungal species that were previously unsuitable due to very high spore mortality.