The failure of lice eradication can often be attributed to poor application. Choose the right method for your situation and ensure that equipment and operators are up to the job.
For those who like to see all the information and simply read through it in order. Each heading is a link to a page of information—the dot point provides a summary of the page.
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Treating sheep for lice
Introduction to lice treatments.
Introduction to backline treatments.
Off-shears backline treatments
Details on applying off-shears backline treatments.
Immersion (plunge and cage) dipping
Introduction to dipping (includes video).
Plunge and cage dipping
Details on how to dip sheep.
Introduction to shower dipping (includes video).
Details on how to shower dip sheep.
Long wool treatments
Introduction to long wool treatments (includes video).
Hand-jetting sheep for lice control
Details on how to jet sheep effectively.
Avoiding dermo at dipping
Management to minimise the spread of dermatophilus when sheep are dipped.
Question and answer
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The choice of application method is dictated by two primary factors:
Some backline/spray-on lice products must be applied within 24 hours after shearing, others can be applied up to 7 days off-shears. As with all lice control treatments, it is essential that every sheep is treated according to the label directions for both dose rate and application timing and pattern.
Some disadvantages of off-shears backline treatments are:
If wool is left too long, or if dermo lesions are present, product dispersal over the skin will be reduced and lice control compromised. Unless sheep are shorn cleanly and are free from dermo, do not use any backline product. These sheep may need to be dipped or culled.
Do not treat ewes while leaving their lambs at foot untreated. If the ewes had lice then some may have spread to their lambs. The lambs will then transfer the lice back to the ewes as the pesticide concentration declines.
Do not treat ewes with a backline product less than six weeks before lambing unless all of the lambs born will be treated with a product registered for the control of lice on unshorn lambs. Backline products take several weeks to control lice. Depending on the product there can still be live lice present on the ewes for six or more weeks after treatment. These will infest lambs if they are born within this time.
Refer to the Ewe-lamb treatments tool for further details.
Most resistance occurs where the same product group is used repeatedly for a number of years. If lice are not eliminated from a flock, it is unwise to use the same product group to treat the sheep in the next year. If treatment is necessary every year, then rotate product groups to reduce the likelihood of resistance development. If resistance is a problem and alternative backline product groups are not available, dipping may be necessary, as it achieves a better distribution of chemical over the sheep.
Underdosing is a major cause of failure with backline products and increases the likelihood that resistance will develop. Most off-shears backline products are applied as low-volume doses, so even a millilitre or so underdosing can represent a significant percentage of the dose. Read the label to determine the correct dose. Dose rates for all registered backline products are determined by the weight of the sheep being treated. Clearly, knowing the weight of the sheep is essential for correct dosing. Weigh a few of the largest sheep in the mob and set the dose for all sheep to that indicated for the heaviest sheep. If there is significant variation in sheep weights, it might be worthwhile to draft the mob into two or more weight classes and adjust dose rates according to the heaviest sheep in each class.
High-volume aqueous diazinon-based products that must be pre-mixed before application, and with doses as high as 225 ml per sheep, cannot be applied with a manual backline applicator. Instead, gas pressure applicators such as the Genesis Power Doser™ or NJ Phillips Powermaster™ Pour-On must be used.
Usually, labels also stipulate the applicator and nozzle that should be used to apply specific products and warn that drench guns are not suitable. Some applicators apply a wide band of product while others apply multiple stripes via a T-bar nozzle. Most off-shears backline products that are sold as ‘ready-to-use’ are applied as low-volume doses that can be comfortably delivered by manual applicators.
The addition of product at the dilution rate indicated on the label at the beginning of dipping.
The selective uptake of pesticide from the dip solution at a faster rate than the removal of water. As a result, the chemical is removed faster than the dip wash, which gradually decreases in concentration as dipping proceeds.
c) Constant replenishment
The ‘constant’ addition of fresh pesticide solution from supply tanks into the dip sump during dipping to maintain a constant volume (and concentration) of dip wash. Advantages of constant replenishment are less fluctuation in dip concentration and no interruption of dipping to replenish or reinforce the dip.
The regular addition of pesticide, but not water, to the dip. Reinforcement replaces the pesticide removed from the dip wash by stripping.
e) Topping up (Replenishment)
The addition of water and pesticide to the dip to replace the dip wash taken out by the sheep. If product label directions say so, topping up should occur after reinforcement, every time the dip volume drops to no less than 75% full.
f) Dipping out
The addition of product only (reinforcement) towards the end of dipping to minimise the amount of used dip wash for disposal. By reinforcing without topping up, dipping out allows the dip volume to drop to 50% full. To determine when to start dipping out, estimate the rate at which wash is being removed from the dip. Calculate how many sheep will take the dip to half its initial volume. Keep the dip at full volume until that number of sheep remain, then begin dipping out. Reinforce when the dip falls to 75% of its initial volume. Continue to dip out until the dip reaches half its initial volume then stop dipping and clean the dip. A dip must not fall below half of the initial level even when dipping out. The dip level should never be low enough to allow the sheep to walk in the dip.
To achieve effective wetting of sheep and ensure eradication of lice by plunge dipping, the swim length should be at least 9m. The sheep should be dunked twice, not including the ‘splash’ entry, to completely wet the head and neck, with a preference towards backward dunking. A large spray nozzle can be used to replace one dunk and would be advantageous in maintaining dip wash circulation.
The dip should be emptied and cleaned when one sheep has been dipped for every 2 litres of the dip's working volume (e.g. for a 10,000 litre dip after 5,000 sheep have been dipped irrespective of how many times topping up has occurred).
Cage dipping is an extremely efficient means of treating large numbers of sheep quickly. Most cage dips are operated by contractors, and a single operator with good dogs can dip several thousand sheep in a day.
No. ‘Richards’ design cage dips operated by ‘Richards-trained’ staff are able to use diazinon to dip sheep for lice. This is because of several unique design features that protect the operator from exposure to dip spray or splash. It is illegal to use diazinon in any other cage dip design or plunge or shower dips. However, there are effective, safer to use alternative products available.
A pressure of 142kPa and a flow rate of 2 l/minute (i.e, fill a 2litre bucket placed anywhere on the floor).
The most important factor affecting sheep wetting is the volume of dip wash delivered from the nozzles. This is determined by pump pressure, the diameter of delivery pipes and the spray nozzles. The pump should supply at least 142 kPa, maintaining high flow rate to the nozzles at this pressure. Some producers have modified their shower dips with larger diameter pipes to increase the volume of dip wash delivered. Common causes of low pressure are worn impellors in the pump or low pump speed.
Check the flow rate and pump pressure. A bucket placed anywhere on the floor of the dip should be filled at a rate of 2 litres per minute. The rotation speed of the top arm should be about 5 revolutions per minute (rpm). High speeds (i.e. above 12 rpm) do not wet sheep thoroughly.
To wet sheep thoroughly they need to be showered using the top nozzles alone for about 12 minutes. Unless you are prepared to shower for this length of time do not use a shower dip as eradication is unlikely to be achieved. Merino sheep look wet much sooner than they are actually wet to the skin where the lice will be. Nozzles must be clean and checked regularly for blockages during dipping.
Jetting, or spray-on applications, to long wool sheep to reduce louse infestations is only a stopgap measure to minimise wool damage until shearing. Lice numbers will be reduced, but the infestation will not be eradicated. Moreover, jetting woolly sheep can cause high insecticide residues in the wool at shearing. Because lice are likely to be present all over the sheep, wetting just the back is not sufficient. The jetting fluid, when applied along the sheep's backline from neck to rump, needs to penetrate to skin level in sufficient volume to allow it to run at skin level down the sides of infested sheep.
700kPa at the handpiece. If two operators are jetting in side-by-side races, the pump must be able to deliver 700 kPa at each handpiece and still provide recirculation.
The pump should be checked before use to ensure it is operating efficiently and adequate fuel should be available. The pump must be capable of delivering 700 kPa (100 psi) at the handpiece while still returning enough jetting fluid via the recirculating hose to provide sufficient mixing in the sump. When the jetting fluid has been mixed, the pump should be started and the handpieces held below the surface of the fluid in the sump in the ‘on’ position for about five minutes. This will provide thorough mixing and ensure the hoses are full of jetting fluid, not just water.
Either a sickle-shaped wand or the Dutjet® wand may be used, although the Dutjet is preferred for ease of use and effectiveness, and sickle shaped wands are now difficult to obtain.
The Dutjet wand has a metal shroud covering the T-shaped delivery tube. The tube has three big bore jets. The shroud has an angled back edge that opens the staple as the wand is drawn along the back of the sheep. This places the jets directly over the opening in the wool so that fluid is directed onto the skin.
22. What is dermo?
‘Dermo’, or more correctly, dermatophilosis, is a skin infection of sheep and occasionally other species, and is also called ‘lumpy wool’. It makes sheep highly susceptible to flystrike, difficult to shear cleanly, interferes with the distribution of backline products, and is highly contagious when wet sheep come into close contact. The disease occurs when the bacterium Dermatophilus congolensis gains access to skin and causes inflammation with exudation of protein and serum from skin, which goes on to form the scabs.
Zinc sulphate heptahydrate at 10kg/1000 l of dip water. Zinc sulphate heptahydrate is registered as a bacteriostat to minimise the spread of dermo between sheep during dipping, but will not have any effect on active lesions. Product labels carry directions for the addition of 10 kg of zinc sulphate heptahydrate per 1000 litres of dip water (1% solution). Some dipping product labels suggest adding chlorhexidine disinfectants (e.g. Hibitane®) for general dip hygiene, but these have no registered claims against the spread of dermo.
An alternative approach to using zinc sulphate is to improve management around dipping to avoid dermo spread e.g. don’t hold wet sheep closely together in yards for extended periods, don’t truck wet sheep or choose not to wet-dip in years when the risks of dermo and subsequent losses are greatest.
When dermo risk is high:
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