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Sheep Lice Control
Lice article- Farming Ahead
Jenny Cotter and Brown Besier
The number of flocks infested with lice in Australia is high and almost certainly increasing. There have been many reports from sheep producers of chemical failure over recent years, and increasing queries on treatment recommendations. Farmers attending a recent series of seminars in Western Australia indicated in feedback surveys that 76% had a problem with sheep lice.
The cost of lice infestations to the industry has been estimated at over $120 million per year nationally. Two thirds of this amount is estimated to be spent on chemicals and labour associated with treatments, with the remaining one third attributed to downgrading of the wool product and a reduction in fleece weight.
Why are lice infestations increasing?
A number of causes are likely to be contributing to the apparently increasing level of infestation. In particular, it is believed that developing resistance to the Insect Growth Regulator (IGR) chemical group is involved. At present there is no practical test to measure lice resistance in the field, but it has been demonstrated in laboratory studies, and confirmed in trials on lice strains where breakdowns have occurred. Resistance is therefore suspected when an explanation for a treatment failure cannot be found after an investigation of farm management and chemical application. While investigations may reveal failures to follow label recommendations or lapses in biosecurity (ie lice are brought onto a property), there are many reports of failure to eradicate lice after the appropriate use of the IGR chemicals Where resistance to one chemical family within a chemical group occurs, cross resistance with other products within that family will also be evident, and lice control or eradication in this situation will require a shift to an unrelated chemical group.
The IGR chemicals enjoy a dominant market share of lice control products and predominantly as the pour-on formulation. When the IGR chemicals are fully efficacious, they greatly assist lice control due to their long period of protection, (Magnum and Zapp have label claims for protection against re- infestation of 12 weeks) Long periods of effective chemical protection provide cover even where breaks in biosecurity occur, and where lice eradication has been difficult due to split shearings or in ewe -lamb transmission situations. A reduction in the protective period after chemical application is an early indication that the chemical is starting to fail, provided that label directions and good biosecurity practices have been followed.
Other than chemical failure, there are several causes that are also likely to be contributing to a rise in sheep lice infestations at present. These relate partly to industry-wide changes to farming enterprises, and also to recently-recognised effects of chemical failure on management.
- Poor application of chemical is still very often the cause of chemical failure. The importance of thorough application of chemical according to label direction whether by dipping showering or backlining is a critical reason for failure to eradicate and cannot be overlooked.
- Low wool prices have reduced the focus on sheep and wool production on many farms, and in turn reduced the need or capacity to invest in chemical, labour and fencing maintenance.
- Increasing numbers of lice-infested flocks due to industry changes fosters lice spread when biosecurity breaks occur. This includes the rise in popularity of meat sheep and shedding breeds and situations where farmers may make economic decisions against lice treatment. In addition, smallholders (or hobby farmers) are often unaware of animal health concerns, and may not recognise the present of lice.
- A level of confusion regarding chemical choice, and lack of awareness of the lice treatment groups. This may apply at both sheep owner and reseller level.
- The use of “split shearings”, especially where farm operations comprise combinations of wool, meat, stud sheep and shedding breeds on the one farm. This means that some flocks may continue to carry lice, when they have been eradicated from other flocks on the farm.
- Limited options for ewe and lamb treatments where there is reduced efficacy of the IGR group, and hence a reduction in the protective period. As with the point above, this means some flocks will remain infested despite treatment of others. Where the IGR’s have failed, there remain only a couple of ewe-lamb treatment options for eradication and these require thought and planning to achieve this outcome with those chemicals.
- Differences in the emphasis on farm biosecurity between farms. Before IGR resistance developed as an industry issue, occasional incursions of lousy sheep across poor fences had less impact in terms of lice spread, due to the “chemical barrier”. In some cases, this may have encouraged a complacent view of biosecurity.
Lice eradication is still possible
Despite the present high levels of lice infestation and severity in sheep flocks, and a reduction in effectiveness of some chemical groups, it is still possible to eradicate lice. The key to eradication or control of lice on sheep properties revolves around product choice, livestock management that takes a whole farm view to impact on the farm lice situation, and an increased emphasis on farm biosecurity. A farm lice plan should be developed for each property, including an assessment of the impact of livestock management decisions on the lice situation.
Farm Lice Plan
Appropriate chemical choice and thorough application according to label instructions is an essential part of the farm lice plan. When selecting a chemical group it is important to know whether a chemical failure is due to a new incursion, or to the presence of lice on the farm. An indication can be gained by recording the extent of signs (rubbings, deranged wool) and when these were first noted after a treatment. Chemical failure is suspected when signs are noted across the treated flocks relatively soon (4-6 months) after a lice treatment. New incursions are more likely to be found in a single flock, and the signs are generally detected later, perhaps 8-12 months after a treatment.
Where failure of the IGR group is suspected on the basis that lice were not eradicated, a treatment option from another chemical group is necessary. For new incursions, the IGR resistance status of a lice population will be unknown and a chemical choice other than IGR groups is generally recommended. This is because most treatments are with IGR’s, and it is therefore likely that any new lice strain will have developed after IGR use on another farm.
Livestock management decisions also impact significantly on the farm lice status. The loss of the long protective period where IGR resistance occurs means it may be necessary to re-think the use of split shearing, and alter management in other areas, such as removing or treating cull sheep immediately, so they do not infest other sheep. Ewe – lamb treatments must be carefully planned as not all chemicals (apart from the IGRs) are registered for use in both ewes and lambs, and there is a risk of re-infestation of ewes if lambs are not effectively treated.
Where possible, an off-shears (short wool) dip of all stock at a single shearing time is most likely to give the best results, as no long-wool treatments are likely to eradicate lice. Although less commonly used, plunge dipping is likely to be most reliable, but shower dipping is effective provided there is attention to ensuring that sheep are thoroughly wetted. In addition, there are spray- on and pour- on options that are also expected to be effective provided correctly applied. However, eradication is not likely with any long wool products, which are considered best used to contain severe lice infestations before treatment at shearing. It should also be noted that resistance to the synthetic pyrethroids (SP) products is widespread, and this group is no longer recommended for routine use.
Sound farm biosecurity is essential to prevent re-infestation. Time and effort put into securing fences will pay dividends. Infestations are obviously less likely in closed flocks, and a shear, treat and quarantine approach should be applied to any sheep brought onto the farm. The current high lice infestation rates indicate the potential risk of introducing lice in purchased sheep.
Eradication or control
Although lice eradication has always been the aim, the new environment in which the IGRs can no longer be relied upon for complete efficacy signals the need for individual property decisions on whether this remains feasible. In particular, the removal of the protection period from re-infestation where IGR resistance occurs will make eradication difficult where split-shearings and ewe-lamb infestations mean that a lice focus survives on a farm despite treatment of part of the flock.
Farmers must decide whether eradication is feasible, or it is necessary to settle for control in their environment. Control should only be used in the short term until new developments enable eradication to become feasible.
Internal factors include the feasibility of altering management decisions such as split –shearings, the timing of ewe and lamb treatments, removing or treating culls, and operating closed flocks.
External factors include the infestation status of neighbouring flocks, the state of fence repair and the attitudes of neighbours towards lice eradication or control. Where these factors can’t be altered in the short term, control strategies may be required due to the potential for re-infestation. In the future, new developments such as a simply-applied test to detect lice or to indicate chemical resistance may allow farmers in a short term control situation to switch to eradication.
Lice and Blowfly Chemical Control Products
Available from July will be a sensitive new laboratory test that can diagnose lice infestations at shearing. Researchers who have developed the test believe it will be highly economical and give producers confidence not to dip or backline as a precautions, as is now done in many cases. The test could be used as part of the management strategy to eradicate lice from properties and or reduce chemical usage and/ or residues in wool. The test uses washings from the cleaning of shearer’s combs and cutters. The laboratory test is the culmination of many years’ financial investment and cooperative research between NSW DPI, Australian Wool Innovation and CSIRO Livestock Industries. The test is to be run at Elizabeth Macarthur Agricultural Institute (EMAI). Camden, NSW. For further information please follow the link to http://www.dpi.nsw.gov.au/research/updates/previous-stories-by-topic/animal/protection/skip-the-dip
Where to get further information on managing lice including products and ewe-lamb treatments
Or for further information on control of lice on sheep contact:
Jenny Cotter DAFWA (08) 9892 8421
Brown Besier DAFWA, (08) 9892 8470