Many compounds shown to be effective against early worm stages in laboratory studies have been generally disappointing when tested in live animals. Treatments administered orally are often broken down by microbes and enzymes in the cattle gut before they can affect worms. Internal Parasites

Homeopathic remedies have also been tested but usually yield disappointing results in structured trials.

Organic drenches have been shown to have measurable effects, but the reduction in worm numbers is generally much less marked than with chemical parasiticides (less than 50% reduction compared to greater than 95% expected from an effective chemical drench). Hence where organic drenches are used management approaches to reduce exposure of young stock to worms are
particularly important.

The question of safety and toxicity with organic treatments is an important one. Just because a treatment is deemed to be organic, it cannot be assumed that it is necessarily not toxic to animals or humans and does not leave residues.

Some compounds tested with possible effect include drenches made from extracts of wormwood (Artemisia spp.), neem, garlic, a range of tropical plant extracts (some of these known to have side effects), cider vinegar, various clay products and diatomaceous earth. Essential oils such as eucalyptus oil, lemon myrtle oil and clove oil have also been suggested, but the concentrations needed could irritate mucous membranes and present a toxicity risk. Copper, often administered as copper sulphate, can provide good effect against barbers pole worm (Haemonchus) but care also needs to be taken to avoid toxicity problems.

With organic treatments for worms it is still important to avoid treating when treatment is not really necessary. Treating older cattle is seldom warranted. In younger stock other diseases or nutritional upsets can cause similar signs to worms so it is wise to get a worm egg count done to confirm a worm problem before treating for worms. Strains of the bacteria Bacillus thuringiensis (B.t.) that kill larval and adult worms have shown promise in research studies. B.t. is registered in Australia for insect control on plants but not for
application to animals.

The nematode trapping fungi, Duddingtonia flagrans, has provided good effects against worms when fed to cattle and is registered for gastrointestinal worm control in some overseas countries. However it is not yet registered in Australia. Duddingtonia does not affect worms in the animal’s gut and is basically a pasture cleaning technology. The spores are eaten by the cattle and then passed out in the faeces to germinate and trap newly hatching worm larvae by means of sticky loops.

External Parasites

Animals can generally tolerate a level of external parasites without suffering any significant production loss. For example, treatment is generally only recommended for buffalo fly when numbers exceed 200 per animal (100 per side). Treatment for ticks is often recommended only when more than 20 ticks larger than 5 mm are seen on one side of several animals. Lice are usually only a
problem in stressed animals and generally cause little production loss, although skin damage, poor appearance and damage to fixtures from animals rubbing can be problems. In most animals lice numbers will fall to non-detectable levels during summer without treatment.

For external parasites, a quite extensive range of compounds, particularly plant extracts, have been demonstrated to have effect as biocides or repellents and a number are currently under research. They can be effective in reducing pest numbers but are
generally less persistent than conventional chemical pesticides and may require frequent re-application. Most organic treatments will not kill lice eggs, necessitating a second application after all of the eggs have hatched, about 2-3 weeks later, to eradicate lice.

The problem of short protection times can be overcome to some degree by self-application with dust bags, back rubbers or rubbing posts. QPIF is currently studying the effectiveness of using these application methods to administer organic treatments for buffalo fly.
The most commonly noted compounds for controlling external parasites are natural pyrethrins, rotenone and sulphur. These are included with synthetic chemicals in some commercial formulations, but only one product containing no synthetic pesticides, a dust containing rotenone and sulphur, is registered for cattle and this only for controlling lice on calves.

Other commonly noted plant extracts shown to have activity against ectoparasites include neem and a range of essential oils, in particular tea tree oil, eucalyptus oil, and geraniol (found in many plants including lemongrass, citrus and geranium). Geraniol has shown good effect against horn flies, a northern hemisphere species closely related to buffalo fly.

A number of parasite control products registered for use on companion animals contain essential oils and eucalyptus oil is a constituent (together with synthetic chemicals). One such project is registered for application to cattle for protecting wounds
against flystrike. Cypress oil extracts have shown activity against ticks in QPIF studies and research into the effects of tea tree oil against buffalo flies and lice is currently underway.

Some other compounds have physical action against ectoparasites. Diatomaceous earth can disrupt the wax layer on the insect cuticle, leading to dehydration and death. Some soaps with a similar action and oils that block the insects’ spiracles (breathing apertures) or directly affect the insect nervous system have also been shown to have effect against ectoparasites. These compounds
are not generally as toxic as chemical pesticides so it is critical to treat animals thoroughly to gain good effect; a number of applications may be necessary.

Some biopesticides have also been shown to be effective against cattle ectoparasites. Different strains of Bacillus thuringiensis (B.t.) have been shown to have effect against buffalo flies, lice and ticks, although they have not been registered for
use on cattle. The fungal biopesticides Metarhizium anisopliae and Beauveria bassiana, which infect lice, ticks and buffalo flies, have shown promise in QPIF studies. Strains of biopesticides vary in efficacy and it is important to choose a suitable strain to fit the use.

Parasitic wasps, similar to those being tested by QPIF for release in feedlots for nuisance fly control, can also parasitise buffalo fly pupae and may help to regulate the size of fly populations. Entomopathogenic nematodes, small worms that can invade and kill insects and some ticks, may be able to attack the pasture phase of flies and ticks; these nematodes have not been tested for
application to cattle. In addition, as previously reported in Beeftalk, QPIF and the University of Queensland have commenced research into the potential of an intracellular bacterium (Wolbachia) as a biocontrol for buffalo fly.

Acknowledgement

Author: Peter James (QDPI)

This article is courtesy of the Queensland Primary Industries and Fisheries - Beeftalk magazine.