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This article was published in 1994
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Organic Farming and Lice Control/Eradication
Gabrielle Morrice, DV, Narrandera
Interest in organic and biodynamic farming is reaching an increasing level both in Narrandera Board and throughout NSW and Australia.
Farmers are entering this type of farming for different reasons. In many there is a generalised dislike of any sort of chemical and so they opt away from their use on-farm. Some have personally experienced health problems in which there is a suggested link with exposure to synthetic chemicals which may have in some way compromised the immune system. Two farmers I know of have shied away from conventional farming techniques for such a reason. Some farmers see organic farming as having a significant potential market both in Australia and overseas. For some of the grain products this market is already being realised, particularly for value-added products such as wheat milled on farm to produce organic flour which is sold to bakeries for the production of 'organic bread'.
For organically produced meat and other animal by-products the market is not as advanced. For meat to be sold as organic certified meat it must be butchered at a certified abattoir. The market for organically produced wool is growing overseas but not in Australia as yet. However, such animals can still bring a premium price at store sales in spite of their often impaired appearance. Unfortunately, although the meat and wool is still not bringing top price, the two main organic certifying bodies in Australia, the National Association for Sustainable Agriculture Australia (NASAA) and Biological Farmers of Australia (Bio Farm) stress that synthetic chemicals must not be used on farms which are certified as being organic. A publication put out by NASAA reads that organic certification means the product has been 'grown by appropriate land management practices without the use of artificial fertilisers, herbicides, pesticides, growth regulators, antibiotics, or hormone stimulants or intensive livestock systems'. Bio farm is more specific and allows (for animal health) the use of herbal and homeopathic remedies; natural pyrethrum, in moderation; magnesite, sulphur, and diatomaceous earth; derris (rotenone) but not to be used near watercourses; natural vitamin supplements, e.g. fish oil and yeast; potassium permanganate; and hydrogen peroxide. Synthetic chemical drenching, vaccines; antibiotics, drugs, ets; and organophosphorous compounds are not allowed.
Organic and biodynamic farmers can face many challenges in the control of weeds, the fertilisation of their soil, the control of noxious animals, and the control of parasites. This is a challenge that many meet head on and adds to the rewards that organic farmers feel they gain from their enterprises. This branch of farming is an expanding one which veterinarians should become more aware of.
lice treatments in sheep have created problems for organic farmers, and in many cases for their neighbours and veterinary advisors. Options available for control and eradication of lice are limited when one considers the commonly available methods and those used frequently by conventional farmers.
Both Bio Farm and NASAA initially allowed the use of Flockmaster (magnesium fluorosilicate plus rotenone plus sulphur) however, this product is not believed to be very effective by some advisors (pers. comm. Peter Johnston, EMAI Camden). NB. NASAA has recently advised that the use of Flockmaster is under review and should not be used by certified producers until further notice (NASAA Bulletin July, 1993). This change of mind was incurred because they decided the compound was a synthetic one and should not be used by organic farmers.
Rotenone (derris dust) works well against itchmite but not against D. ovis. Weight for weight it is not as toxic as other treatments and therefore an increased level would be needed for the treatment of lice.
Azadirachtin is an insecticide extracted from the seeds of the neem tree. It is effective against a wide range of pests, but is non-toxic to humans and other mammals. The neem tree is a member of the family Meliaceae and is related to the white cedar tree. It is well adapted to hot, seasonally dry regions within the tropics and, although there are relatively few in Australia currently it should adapt well to dry tropical parts of northern Australia.
At low concentrations, azadirachtin disrupts the pest's normal pattern of growth and development, sometimes causing death; at higher concentrations, azadirachtins still disrupt growth and development. They also trigger the pest's physioligical reaction to adverse conditions, cancelling their drives to feed and lay eggs; at even higher concentrations, they retain all of the above effects; they will also repel the pests even without coming into contact with them. There is no evidence that azadirachtins affect fish, earthworms or honey bees. As yet, research has revealed no evidence of the development of resistance by susceptible pests to azadirachtins.
Azadirachtins are not yet commercially available but some trials have been carried out to evaluate its effectiveness. A data sheet put out by Ausneem states that 2 grams of a zadirachtin per sheep will provide 30 weeks protection against lice. Sydney Uni trials found that using 4 grams per sheep gave 100% kill of lice. However, this costs approximately $7.50 per sheep. Azadirachtin is also very susceptible to UV breakdown. 19 mm of wool is believed to be ideal to prevent this and therefore sheep must be treated at three to four weeks post shearing. (pers. comm.. Michael Burlace, NSW Ag., Orange).
The use of a suitable medium for the application of azadirachtin also needs further investigation. Current research is hampered by a shortage of the product and its extremely high price. However, this product does show great promise for use against a variety of pests. (Ref. old DPI Farmnote: Neem trees, source of a natural insecticide).
Pyrethrum takes four to five days to kill lice and is very susceptible to UV breakdown. Therefore as yet it has not been found to be suitable as a lice treatment. Further work is being conducted using genetic manipulation of the crysanthemum plant to enhance the use of this naturally occurring insecticide.
Bluestone/Sulphur: A deficiency of zinc and sulphur are believed to contribute to damage caused by/or susceptibility to itchmite, lice, strike and lumpy wool. Some organic farmers use Fernies 12.5% sulphur blocks (Dubbo) to increase the natural resistance of their sheep to such problems.
The use of sulphur supplementation may only be of use on basalt soils (black soils) where sulphur deficiency is known to be a problem. (Pers. comm., Dr. Arch Sinclair).
Some organic farmers also use lugol's solution (idodine/sulphur) as a dip and feel that this given good control.
The February 1994 edition of Control and Therapy contained an unsubstantiated note on the use of 'Maxicrop' (liquefied seaweed) for the control of cattle tick. The suggestion was that the organic iodine would increase the rate of synthesis of thyroxin which would then repel fleas, lice and ticks. Thyroid hormones are necessary for skin and hair integrity. But as iodine toxicity can occur if an excess is given, the iodine status of the area/animals should be known before supplementation is implemented. I could find no information on the effect of oral iodine supplementation on lice control in sheep.
One organic farmer claims he gets one month's protection from the use of a garlic drench. However, one must question the value of such a short duration of protection if it works at all.
Selective breeding and genetic resistance should be investigated as a means for long term control and reduction of the effects of lice as it is generally believed that some sheep are genetically more resistant to lice than others.
I am interested in the acceptance of the two main regulatory bodies for organic farmers of the concept of using a conventional dip off the registered farm and keeping the sheep off such a farm until there was a very low residual of such a chemical. Bio Farm will accept a maximum of 2% of the MRL. NASAA will allow the treatment of sheep off farm with synthetic chemicals as long as the sheep themselves are not certified (i.e. it is a mixed farm). The sheep would have to be quarantined off the certified area for three weeks or three times the withholding period (presumably whichever is longest). This would not be considered suitable in cases where the wool is being sold as certified organic wool. If dipping was carried out correctly; a closed flock maintained; and fences were maintained to a high standard, only one such dipping should be necessary. Such a method would not be acceptable to biodynamic farmers but may be acceptable to some of the organic farmers.
All organic farmers should maintain good fences to reduce the possibility of infecting neighbours' sheep or of having their own sheep reinfected. This would also help to keep the use of any chemical to a minimum, synthetic or natural, which is another of the principals which organic certified farmers must follow. They should try to work in closely with their conventional neighbours to reduce friction as well as cross infection.
The mode of action of irritation of lice in sheep is not completely understood. It is possible that sheep absorb antigens associated with lice which causes a hypersensitivity or allergic reaction in association with some physical irritation. As such perhaps there is a need to look at the production of a vaccine to reduce the hypersensitivity. The hapten is as yet unknown, or at least undocumented. Work conducted by A.W. Sinclair et al. published in Veterinary Parasitology, 30 (1989) 233-251, suggested that 'mechanical stimuli by feeding lice seem an unlikely source of signals to epidermal sensors such as Merkel cells'. These are located in the basal layer (Lyne and Hollis, 1971), yet lice feed only at loose outer stratum corneum covered by lipid emulsion (Lloyd et al., 1979; Britt et al. 1985, 1986). Sensory nerve endings are not found in sheep epidermis after birth (Lyne and Hollis, 1972).
'If mechanical stimuli are not the source of host irritation, there remains the possibility of host sensitisation to components of louse saliva or excreta. The lipid content of excrete could interfere with antigenic activity, which would explain the lack of response to intradermal injections of excreta suspended in saline .... Possibly fractionation of the brei and removal of lipid may provide more precise information. If louse saliva is the sensitising agent, some elegant technology may be needed to test this'.
In the same paper it was stated that 'unpublished observations on infested sheep flocks suggest a lack of a direct relationship between louse numbers and intensity or duration of rubbing, scratching or biting'. This observation also points to a sensitisation being involved in the reaction of sheep to lice infestation.
When contacted, Dr. Sinclair now feels that there may be a very slight immunological reaction but not enough to institute the use of vaccine (pers. comm.).