Sheep Body Lice: Control and Eradication

Note Number: AG1110
Published: October 2003
Updated: September 2009

 

Introduction

Failure to prevent, control and eradicate sheep lice can have an impact on the profitability of farms deriving income from wool production. If not controlled, lice infestations can reduce wool cuts and increase the volume of wool in inferior lines. Sheep do not generally suffer losses in bodyweight due to lice but animals in poorer health due to internal parasites or nutrition tend to carry heavier burdens of body lice.

All good farm animal health programs rely on the same principles. Prevention of disease is by far the easiest and cheapest method of disease control. Good health monitoring and surveillance will enable early detection of disease. Early detection of disease will allow an effectiveeradication program to be developed.

Prevention

Prevention is the best way to minimise the impact of lice on farm. Lice spread primarily by direct contact between sheep: they are host specific and cannot live off sheep for very long. What this means is the most likely source of new infestation is from sheep. Lice are unlikely to be transmitted by wool on posts or fences or picked up from long grass and trees. With this in mind controlling the movement of sheep is the most critical aspect of lice infestations, and there are several strategies to employ to prevent the introduction of lousy sheep into your flock.

Fencing

Fencing needs to be sheep proof at all times. Pay particular attention to boundary fencing, roadways, creek crossings, drains and timber plantations. With the advent of Landcare; increased environmental work on farm, and the increase of timber plantations, the risk of stray sheep has increased because stray sheep can hide undetected in fenced off creeks, gullies and plantations. Further, some timber companies lease out the grazing rights to their plantations as a means of grass control and fire mitigation. Often new plantations have been established on old farm land and retain several watering points making it difficult to detect and remove sheep. These stray sheep can breach boundary fencing and mingle undetected with your sheep.

Introducing new sheep

Most farms introduce sheep at some time, whether as breeding stock, to bolster numbers, stores to fatten, or sheep on agistment. These introductions represent another possible source of infection. By having “stock proof” internal fencing, these risks can be managed by quarantining the introductions from other sheep until you can be sure they are not carrying a lice infestation (at their next shearing). Inspections should be carried out prior to introducing them on to the farm, but light infestations or short wool will make detecting lice very difficult. Good record keeping of introductions and mob movements around the farm will help in managing these risks. While not mandatory, it is good policy to issue and request a Sheep Health Statement when moving sheep on and off farm. These can be downloaded from the DPI website or are available from DPI offices.

Be a good neighbour

Good biosecurity should also exist between neighbours. Talk to neighbours and request that should they find one of your sheep on their farm they do not put it back over the fence. Get them to ring you for your collection and management of the straying sheep: you don’t know if the neighbour has lice or how long your sheep has been with theirs.

If in doubt, destroy the sheep as it is better to sacrifice one sheep than to risk your whole flock. If a number of sheep have strayed treat them as you would for any other new sheep introduced to your property.

Buffer zones

Make assessments of the farm and use natural barriers or buffer zones. The creation of buffer zones further enhances biosecurity providing you with an area free from livestock to help prevent disease spread, including lice. Such buffer zones can be created using unused roads, old railway lines, creeks and rivers etc.

Arrange an agreement with the neighbours that these zones do not carry stock. Have a policy about what happens to sheep caught in these buffer zones. Do you really want them back?

Non sheep vectors

Consideration should be given to shearing teams. There is potential for adult lice to live in shearing footwear such as shearers moccasins for up to ten days.

While the risk might be small, all risks should be analysed given the cost of a lice infestation on farm. If shearers have previously worked at a shed with a heavy infestation, adult lice could be transferred to your sheep inadvertently. Microwaving moccasins for 5 min is a quick and convenient way of minimising the risk of transfer.

Early Detection

All good stock mangers are on the look out for disease; lice should be no different. When performing normal animal husbandry routines on the farm make random inspections of suspicious looking animals and always look for the signs of lice. Rubbing on posts and trees, biting at wool and wool on the fences are all signs that sheep are itchy. Itching and rubbing sheep does not necessarily indicate lice, but it should raise suspicions. Always inspect new introductions very carefully.

Lice can be difficult to detect and many partings of the wool might be necessary to find them. It is critical to actually see lice before an eradication program is initiated and it is important to actually identify the sheep body louse (see Agnote 1109 Sheep Body Lice).

There are several other causes of sheep rubbing that are not lice. The treatment of sheep for lice is expensive, time consuming and with every extra chemical treatment hastens the risk of the development of resistance. If sheep body lice are detected then eradication and future prevention is necessary.

Inspections prior to shearing are critical. This is crucial to decision making if lice are detected because shearing and post shearing treatment is a key component in eradicating lice. Shearing can remove up to 90% of lice on the sheep and these will consequently die in the wool bale. The secret to successful eradication is the treatment post shearing.

If lice are detected several months prior to shearing then several factors need to be considered prior to embarking on eradication.

The level of infestation will determine the best course of action. The damage to wool caused by a light infestation may not warrant the cost treatment until shearing.

Eradication

Testing

Detection of lice has now been made easier with the development of a lice detection kit to be used at shearing. Low levels of lice are difficult to detect but the kit will detect infestations at very low levels.

The test works by detecting a unique protein found in sheep lice. When lousy sheep are shorn the protein is trapped on the wool grease left on the comb and cutter. The kit enables producers to collect the wool grease from suspect mobs and submit the sample to the laboratory for testing.

For further information, or to request a kit, contact Paul Young or Narelle Sales of Industry & Investment NSW on 02 4640 6433. (paul.young@industry.nsw.gov.au or narelle.sales@industry.nsw.gov.au)

Shearing and treatment to eradicate lice

Chemical applications in long wool will not eradicate lice. A full eradication effort will be required post shearing, therefore, consideration needs to be given to how long before the next shearing. Most chemicals will have withholding periods for wool, meat and an export slaughter interval. This will impact on what products can be used. Shearing may be brought forward to avoid the need to treat for lice in long wool.

Lambing

Pregnant ewes and ewes with lambs at foot can present a serious challenge to a lice eradication program because it is essential that ALL sheep are treated for any lice eradication program to be successful. An isolation period of 6 weeks should be observed prior to mixing treated and non treated sheep.

The use of some chemicals (particularly the Insect Growth Regulators - IGRs) will limit the ability for sheep to be mixed for a period of time post treatment. For the same reasons, pregnant ewes should not be treated within 6 weeks of lambing.

Animal welfare concerns should be considered with respect to dipping ewes and lambs. Dipping of late pregnant ewes and young lambs should not be considered due to the risk of stress and subsequent welfare consequences.

I’ve got lice - what are my options?

Disposing of lousy sheep at saleyards is not an option and is illegal. If disposal rather than treatment is a considered option there are methods of disposal available to producers that have lousy sheep which require permission from a DPI authorised inspector of livestock. To discuss theses options please contact your local DPI animal health staff member.

If treatment is being considered, several methods are available to treat sheep infested with lice (see Table 1). Effective chemical treatment requires adherence to several key principles.

Rotate chemical groups.

Several different chemical groups have been used to kill lice. Some groups have lost their effectiveness and should not be considered. Of the effective chemicals, it is important to rotate to a different chemical group every time you treat for lice.

Read the label.

Always read and follow label instructions. For chemicals to effectively kill lice they need to be applied at the correct rate at the correct time, and for the required length of time. Failure to follow the instruction may result in a sub lethal kill. This will increase the need to retreat next year, increase the risk of developing resistance, and cost money.

Observe Withholding Periods (WHP)

Australia enjoys market access to many countries around the world because we can assure them the products we produce are safe. Sales of animal or animal products that are sold for human consumption detected with chemicals above the Maximum Residue Limit (MRL) threaten international trade, domestic market confidence, and can result in prosecution.

It is very important to observe the withholding periods stated on the label:

The wool withholding period is the time the product should not be used before shearing. This ensures there are no chemical residues in the wool.

The meat withholding (or export slaughter) interval is the period of time after treatment that animals should not be sold for human consumption.

Where the milk from sheep may be used for human consumption the withholding period for milk should be observed.

Keep accurate records

Keeping accurate records is an excellent way of understanding and observing withholding periods. Under the Agricultural & Veterinary Chemicals Regulations any person applying veterinary chemicals for which a withholding period applies must keep accurate records. Details of what records are to be kept can be found on the DPI website in General Farming / Chemical use.

Chemicals for controlling lice.

Organophosphates (OPs) until recently were the main chemicals used for controlling lice in sheep. The most commonly used OP contained the active ingredient diazinon. In May 2007 products containing diazinon were suspended from use for dipping and jetting sheep. From May 2009 it is illegal to treat sheep with diazinon by jetting or dipping unless under special permit.

Insect Growth Regulators (IGRs) inhibit the growth and development of lice to break the life cycle of the insect. As they do not kill adult lice they are not generally recommended for late pregnant ewes, or where recently-treated sheep are to be mixed with untreated, lice-free sheep.

Research undertaken collaboratively by Queensland DPI and Industry & Investment NSW have identified strains of lice with reduced susceptibility to IGRs. Over the last two years there have been an increasing number of reports of suspected resistance.

Synthetic Pyrethroids (SPs) interfere with the insect’s nervous system. They are not as dangerous to humans as OP’s, but can have a devastating affect on aquatic life if contamination of waterways occurs. Lice resistance to these chemicals are commonplace now. For these two reasons, the use of synthetic pyrethroids is no longer recommended.

Macrocyclic Lactones (MLs) (ivermectin) also affect the insect’s nervous system and are used for long wool treatments by means of hand jetting. Follow up treatment off shears is recommended after using any long wool product to eradicate lice.

Spinosyn (SPINs) (Extinosad): causes nerve dysfunction in insects, with negligible human health and environmental risks.

Other registered chemicals (i.e. not OPs, IGRs, MLs) such as magnesium fluorosilicate can be used for treating lice-infected sheep. Magnesium fluorosilicate will control body lice and is approved for organic production enterprises. Its mode of action is to severely and rapidly dehydrate lice.

New chemicals could become available after the publication of this Information Note.

Acknowledgements

The original authors of this information note were Louise Wood, Katie Rutter and Richard Keys, and the previous version was published in October 2003.

It was reviewed by:

Peter Corbet, June 2007.

Leon Watts, Farm Services Victoria – Animal Health Field Services. September 2009.

 

 

Table 1. Sheep lice treatments

Method	Ideal wool length	Equipment required	Advantages	Disadvantages	Comments
Plunge Dip	3 weeks off shears (maximum 6 weeks)	Plunge dip (own, or contractor’s) Personal protective equipment.	Very effective if performed correctly	Expensive to set up own facilities Bacterial infections can be spread Labour intensive	Dip concentration needs to be maintained Disinfectant can be added to reduce bacterial infection Essential that sheep are submerged for correct amount of time
Shower Dip	2-3 weeks off shears (maximum 6 weeks)	Shower dip facilities Personal protective equipment.	Less labour intensive	Expensive to set up facilities, and more difficult to maintain Generally less effective More chance of failure due to difficulties in achieving thorough saturation More operator exposure to chemical	Dip concentration needs to be maintained All nozzles and operation must be checked prior to start Disinfectant can be added to reduce bacterial infection
Off-shears Backline	Immediately after shearing (<24 hours, unless stated otherwise by manufacturer)	Sheep race Suitable applicator gun and backpack Personal protective equipment.	Less labour intensive Low capital outlay and maintenance No discharge of used dipwash necessary	Avoid use of synthetic pyrethroid products Slow to kill lice High chemical cost Effectiveness reduced if sheep not cleanly shorn	Must be applied evenly on entire backline, from poll to tail. Pregnant ewes should not be treated unless manufacturer states otherwise
Long-wool Backline	6 weeks to 10 months wool (observe withhold periods!)	Sheep race Suitable applicator gun and backpack Personal protective equipment.	Less labour intensive Low capital outlay and maintenance No discharge of used dipwash necessary	Potential for heavy chemical residues – avoid use of synthetic pyrethroid products Slow to kill lice High chemical cost Effectiveness reduced if lice are resistant to active ingredient	Must be applied evenly on entire backline, from poll to tail.
Jetting	Long wool treatment for control only, if required	Yards and jetting equipment	Control lice until eradication at shearing	Control only Possible wool residue problems A slow and tedious operation	Requires appropriate equipment in good condition, and thorough application