Page 14 - April 2008 The Game
P. 14

14 The Game, April 2008
Canada’s Thoroughbred Racing Newspaper
mentally friendly as it has no measur- able impact on soil microfauna and does not persist in the soil after killing off the parasites.” He expects the fungus to have an international market, as livestock producers face ever increasing parasite resistance to chemical means of control. “It’s a clean, green method of reducing the parasite burden which can be used
he future of chemical parasite to trap and kill worms. It zeroes in control is not a pretty one. on developing nematode larvae in
was successfully used as a biological control agent against the free-living larval stages of horse strongyles. A horse known to be carrying a heavy parasite load of small strongyles was used as the source of manure contain- ing worm eggs for the study. Manure was collected before the horse was fed the fungus, and then D.  agrans was then fed to the horse at the rate
of 106 fungal spores/kg body weight/ day on four consecutive days. Manure was collected again after the third
Parasitologists say there is increasing evidence world-wide that equine worms are becoming resis- tant to most, if not all, of the major classes of deworming drugs. What’s worse, there are precious few new medications in development. Here
in North America, horse-owners and trainers have been lucky: we can still depend on ivermectin to kill most forms of equine parasites, and so far, there have been few signs of resis- tance to this versatile, effective, and extremely safe drug. But all the evidence points to our living on borrowed time there, too. There have been documented cases of ivermectin- resistant worm populations in other livestock species, and in horses else- where in the world.... so it’s coming, folks, and there’s not much we can do about it.
manure on pasture, weaving a dense, contractile web of  laments around them and then penetrating the skins of the worms and infecting them with fungal spores. And it has gained
That’s why alternate forms of parasite control are beginning to be taken more and more seriously. And some of them come from the most unlikely of places.
The result? On average, pasture surrounding fecal pats containing Duddingtonia  agrans had 94.8% fewer worm larvae.
What’s more, D.  agrans seems
to be equally insatiable in all sorts
of different animal manures, and targets a wide range of parasitic nematodes, including the danger-
ous small strongyles, in  eld studies conducted under a broad spectrum
of climatic conditions. Whether it’s northern Europe, southern Australia, or midwestern North America, the fungus seems equally keen to do its duty.
Consider, for example, a friendly fungus with the rather geeky name of Duddingtonia  agrans. D.  agrans is one of more than 150 naturally- occurring fungus species which live
In one study carried out at the Royal Veterinary and Agricultural University`s farm near Copenhagen, a new isolate of the fungus D.  agrans
The friendly fungus has attracted considerable attention from Austra- lian scientists, who are grappling with serious resistance issues in sheep and cattle parasites. At the Commonwealth Scienti c and Industrial Research Organisation (CSIRO), research-
ers partnered with the Sydney-based company, International Animal Health Products Pty Ltd., have been tinkering with D.  agrans to discover the best way to incorporate it into animal feeds. CSIRO Livestock Industries Princi- pal Research Scientist, Dr Malcolm Knox, says, “The fungus is environ-
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Some questions remain, of course. The fungus would have to be fed on a regular basis to be effective, and the pattern of administration would be dependent to some extent on seasonal patterns of nematode transmission in your local area. How completely the fungus eliminated worms from pasture would determine the necessity and
the attention of researchers because D.  agrans has a particular talent
for surviving passage through the mammalian digestive tract. Harness- ing this biological buddy may soon help ease our reliance on chemical forms of control and provide us with a more integrated approach to parasite combat.
day of fungal administration. Ten
1 kg fecal pats,  ve with the fungus and  ve without, were each placed on small square plots of pasture, on three occasions during the summer in June, July and August. Finally, samples
of the surrounding vegetation were taken every two weeks for an eight- week stretch, to detect worm larvae migrating out of the manure onto the plants. The worm larvae collected from each plot were counted and identi ed.
in conjunction with a range of other control strategies,” he says.
In trials, D.  agrans, fed in the form of a small amount of grain coated with the spores, has successfully reduced small strongyle populations in groups of horses both in the cool climate of Denmark and the subtropical one of Louisiana. It seems to be extremely effective against many species of parasitic nematodes (in fact its activity has been described as “voracious”), not only in horses but also in cattle, pigs, and lambs, with no adverse effect on the animals – the fungi only germinate once passed in the manure.
In Australian  eld trials involv-
ing feeding the spores with a grain supplement had proven that a high level of parasite control could be achieved. Nematode numbers were reduced by about 75 per cent in experiments using sheep and up to 90 per cent with horses.
Equine Health
By Karen Briggs
Dave Landry Photo
timing of further treatments.
But these are fairly minor stumbling blocks, far outweighed
by the prospect of such an environ- mentally-friendly, low-impact way of controlling worms as nature intended. Should feeds inoculated with D.  agrans become commercially available soon
(as seems likely), we’ll be able to reduce our depen- dence on chemical means of parasite control and thus prolong the useful life of the drugs we do have.
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