TBNSW Breeders Update Winter/Spring 2018 - Page 31



ADVERTORIAL
BIOLOGICAL
CONTROL
OF HORSE
ROUNDWORMS
Feeding a natural fungus to horses can provide an effective
alternative to chemical drenches to control worm parasites, by
means of biological control. Rather than trying to cure round worm
infestations with drugs, the aim is to break the worm life cycle by
preventing livestock ingesting infective larvae when grazing.
Mode of action: Australian strains of the nematode-destroying
fungus, Duddingtonia flagrans, were first discovered in a CSIRO
farm survey during the early 1990s. When fed to horses, the fungal
spores pass through the gut of the animal and are excreted with
the worm eggs in the dung. The fungal spores then germinate and
grow networks of traps which ensnare and kill the worm larvae
soon after they emerge from the eggs. The adult worms living
in the animals do not live forever, so this cycle of constant reinfection is required to maintain the worm infestation in the horses.
Results of Australian field studies in horses: Placebo controlled
studies were conducted according to Good Clinical Practice
standards by an independent contractor, in which the animals
were fed the fungal spores dispersed in a nutritional supplement
(placebo). The trials were undertaken in different seasons and
climatic regions. In these trials efficacy was measured by direct
counting of larval numbers on pasture over an 8 week period. A
typical result is shown below. Over all five trials the reduction in
larval numbers averaged 84 % (Healey, Lawlor et al., 2018).
Residue studies: Laboratory studies by expert chemists
showed that any residues produced by the fungus were below
the appropriate European Union Safety guidelines. Further,
investigation by specialist toxicologists showed freedom from
undesirable characteristics such as genotoxicity.
Ease of use: The fungus is easy to use, by means of daily
administration in a nutritional supplement or in rations. For best
results, firstly perform a faecal egg count and if appropriate
the horses should be treated with an effective chemical drench
(avoiding total elimination of worms as young horses need to
develop immunity), and then the fungus is fed to maintain their
low-worm status. Ideally, the animals would also be moved at
this stage onto pasture that had been rested to allow its burden
of parasite larvae to die off (minimum 6 weeks). Alternately, a
paddock that has been cross-grazed with another species of
animal can be used. However, it is important to bear in mind the
process of refugia management (see Wormboss guidelines for
more about this) and to remember that the fungus will not affect
worm larvae that have already emerged on the pasture.
Environmental impact of the fungus: CSIRO researchers
also investigated the possible adverse effects of D. flagrans on
beneficial soil organisms in a typical improved pasture (Knox et
al., 2002). The presence of fungi in livestock faeces did not affect
the abundance of beneficial soil nematodes and microarthropods.
There were also no negative effects of fungal presence on the
numbers of other nematode-trapping fungi. Over time, there was
generally a decline in the presence of the fungi and the rate of decline
appeared to depend on seasonal conditions. Drier conditions
appeared to prolong the presence of the fungi in faecal matter.
The main parasites encountered in the Australian horse trials
included Small Strongyles (cyathostomes), Large Strongyles
(Strongylus spp.), and Stomach Hair Worms (Trichostrongylus axei).
Safety: Long term safety studies were conducted in horses
with the fungus fed at 10X dose over an 8 week period with no
harm detected. Also, a suite of safety studies were conducted in
laboratory animals, which showed the fungus is not infective or
toxic, meaning it is safe for farmers to handle.
Numerous other studies around the world have shown similar
results and have demonstrated absence of impact on dung beetles
and earthworms.
Regulatory Approval: The APVMA granted registration of two
products containing a CSIRO isolate of D. flagrans (IAH 1297) for
control of gastrointestinal nematodes in grazing animal animals,
namely BioWorma® and Livamol® with BioWorma®. These
products are made by Australian-owned International Animal Health
Products Pty Ltd, who began collaboration with CSIRO in 1997.

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