1. USDA ARS, Dale Bumpers Small Farms Research Center Booneville, Arkansas
2. Louisiana State University Baton Rouge, Louisiana
Reproduced with permission from the original authors and the American Consortium for Small Ruminant Parasite Control.
To understand how nematode-trapping fungus might help, a basic understanding of the worm life cycle is necessary. Briefly, the worm life cycle of nematodes (including scour worms, barber's pole worm and Nematodirus) consists of two parts: one that takes place inside the animal and one that occurs on pasture. Adult worms reside in the gastrointestinal tract of the animal and after mating, female worms lay eggs that are passed out in the faeces. The eggs hatch in the faeces and develop through two larval stages until reaching the third larval stage that migrates out onto the surrounding vegetation where it is ready to be consumed by grazing animals. Once ingested, the larvae develop into adult worms (which do damage to the host animal) and the life cycle is complete. When an animal is dewormed (or drenched), worms inside the animals are eliminated which reduces the number of worm eggs that are passed in the faeces to contaminate the pasture. The more worms that drenches kill, the fewer the number of eggs on pasture, but eventually worms become resistant to drenches and egg shedding returns to higher levels. Reliance on drenches for worm burden within the animal and on the pasture has proven to be unsustainable. Besides drenching, an integrated approach is needed for good practice worm control. This involves combining timely, effective drenching with other control strategies. These include:
Grazing Management—Preparing ‘low worm-risk’ pastures for susceptible sheep such as weaners and late pregnant or lactating ewes;
Nutrition—Well-grown weaners develop immunity earlier. Well-fed lambing ewes shed fewer worm eggs and produce more productive lambs;
Breeding for worm resistance—Buying rams bred for increased resistance to worms. Select those with favourable Australian Sheep Breeding Values (ASBVs) for worm egg count (WEC) as well as favourable values for the production traits you want;
Manage and monitor—Regularly monitor worm burdens and drench efficacy using WormTests and DrenchTests.
Reducing the population of worms on pasture can reduce the reliance on drenches as a means of worm control. Nematode-trapping fungi specifically target the worm population on pasture, effectively breaking the worm-cycle, and could be considered as part of an integrated approach to worm control.
Nematode-trapping fungi have been shown to be efficient biological control agents against the worm larvae in livestock faeces. These fungi are found naturally in environments that are rich in organic matter where they produce a variety of mycelial (vegetative part of the fungus) structures that trap, destroy, and feed on non-parasitic soil worms. Spores of various species of these fungi have been isolated, concentrated, and introduced into faeces that contain developing gastrointestinal worm larvae. Of those investigated in livestock, Duddingtonia flagrans spores (Figure 1) have the best ability to survive passage through the ruminant gastrointestinal tract. When passed in the faeces, D. flagrans spores germinate. The mycelia grow rapidly into sticky, sophisticated traps/loops that trap and digest larvae (Figure 2).
Micrograph images copyright International Animal Health Products Pty Ltd
The trapping structures are usually present within the first few hours after defecation, and a sticky substance is present within 48 hours to help with larval contact, followed by hyphal cuticle penetration (Figures 3 and 4). The moving parasitic larvae are trapped by the structures of the mycelium. Once the larvae are trapped, the hyphae penetrate the larval cuticle and grow, filling the body of the larvae and digesting the contents. Most importantly, trapped larvae are unable to migrate out of the faecal mass and onto pasture that could be consumed by the grazing host animal. Fewer larvae on pasture result in healthier animals.
Micrograph images copyright International Animal Health Products Pty Ltd
The primary delivery system of the spore material is thorough mixing with supplementary feedstuffs which provides a continuous source of the fungus in the faeces. Daily feeding so that each animal consumes an adequate amount of the feed/spore mixture is necessary. Another delivery system would be thoroughly mixing the fungal spore material into a loose mineral supplement. The mineral would need to be kept covered and dry. This method does not require daily feeding, but the mineral supplement would need to be available and regularly consumed to provide a constant source of spores for the duration of the treatment period. There has been little research on this method, but it would provide a good alternative for producers who do not provide supplementary feed to their livestock. Unfortunately, the spores cannot be incorporated into pellets or cooked blocks as the heat of the pelleting process will kill the spores. To achieve adequate control of larvae in the faeces during the transmission season, spores would need to be fed for a period of at least 60 to 120 days. Feeding should commence with the beginning of the grazing season, especially for young freshly weaned livestock (in Australia, stock are grazed all year round, and feeding the spores may need to be done throughout the year or or to match the conditions that suit egg development to larvae). Similarly, to help curb the periparturient egg rise, feeding spores to females during late pregnancy and lactation should help to reduce pasture contamination for lambs/kids that graze the same pastures with their dams. Feeding studies with sheep, goats, and cattle have shown a reduction of 68 to 86 percent of larvae in faeces and on pasture. Worm egg counts can be expected to decrease over time due to the reduced reinfection. During periods of drought or low transmission (winter and other non-grazing periods), it would not be necessary to feed spores as there would already be a reduced number of larvae in the faeces. There would also be no need to feed the spores to animals being raised in confinement, since there is little to no source of parasitic infection.
In Australia, two formulations of Duddingtonia flagrans are APVMA-approved and commercially available from registered and approved retailers, feed and farm stores: BioWorma®, and Livamol® with BioWorma®. Livamol® with BioWorma® is a protein supplement that can be mixed with other feed supplements or top-dressed over feed. BioWorma® is a concentrated feed additive that is meant to be mixed with other feeds or supplements. The cost of feeding BioWorma® is relatively expensive compared to drenches, but the long-term benefit of reduced pasture contamination is a factor that must be considered. In addition, it is possible that research will determine more cost-effective ways to utilize BioWorma©. For example, feeding BioWorma© every other day or for two weeks out of the month would reduce cost by half if it is proven to be as effective as daily feeding.
Both products are the only control method that specifically targets the worm population on pasture, where the majority (estimated at more than 90 percent) of the total worm population resides during the parasite season. This form of control has been successfully applied under field conditions and is an environmentally-safe, biological approach for pasture-based livestock production. When introducing anything new into the environment, the long-term effect on trapping advantageous native free-living worms that help recycle faecal matter also needs to be considered. It has been demonstrated that D. flagrans had no adverse effect on such advantageous worms, and the fungus was no longer detectable in the environment two months after treatment. It is important to understand and emphasise that these products are just one component of an integrated parasite control program and should not be relied on alone for gastrointestinal worm control. One still needs to address the worm population in the animal using drenches most effective on your property and, in Australia, should consult the WormBoss worm control program for your region which includes practical strategies relevant to the region on grazing management, breeding for worm resistance, when to drench and when to WormTest, and managing drench resistance.
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