CASE NOTES

Introducing Flexolt^® the only oral sheep lice control product

Felicity Wills, Ruminant Technical Advisor, MSD Animal Health

Posted Flock and Herd November 2024

Introduction

Flexolt^® is the first ever oral lice treatment for sheep, giving producers the ultimate flexibility when it comes to treating their flock. The world-first product can be used on both sheep and lambs*, with any length of wool, revolutionising how and when producers can administer a sheep lice treatment.

THE ACTIVE

Flexolt contains the active ingredient, fluralaner (10g/L), which is part of the isoxazoline class, a novel class for lice treatment in sheep. Fluralaner has a unique mode of action as an antagonist of ligan gated chloride channels, which results in potent blockage of both GABA-gated and L-glutamate-gated chloride channels. The blockage of the ligan gated chloride channels interferes with the arthropod nervous system resulting in death but does not affect mammalian species. After being administered orally, fluralaner is absorbed into the plasma and bound to protein. It is then excreted through fibre follicles onto the skin surface. Fluralaner displays excellent contact and ingestion activity against Bovicola ovis (sheep lice)

TRIAL WORK

As part of the development of Flexolt, 15 field trials run under commercial conditions were conducted across Australia, undertaken by independent researchers to demonstrate that the product is effective across different sheep operations, locations, wool types, and wool lengths. The requirement of these studies was to achieve "elimination of all live lice and viable eggs from treated animals, as determined by inspection of sheep 20 weeks after treatment". The outcome of these trials showed that all live lice were killed by 21 days post-treatment and no live lice or viable eggs at 20 weeks post-treatment. There was one trial that did not achieve this standard, achieving 99.6% control. This trial was conducted on ewes off-shears and of the 50 sheep inspected at 20 weeks post-treatment, 1 sheep had 22 lice counted and 2 sheep had 1 louse each. The tracer sheep had been yarded overnight prior to inspection and the single louse found on two sheep is suspected to be transfer. It was noted in this trial that ewes coughed significantly at administration. Trial protocol did not allow sheep to be re-dosed even if it was suspected to have coughed up some/all of the dose.

An additional trial was running concurrently on this property in ewes treated 7 days off-shears. In this trial coughing was not reported and no live lice or viable eggs were present at 20 weeks post-treatment. This highlights the need for accurate dosing. Flexolt has a very wide safety margin (5 times the normal dose showed no adverse effects) so it is recommended that if a sheep is suspected to have coughed up or not received a full dose they should be retreated. Coughing is listed as a precaution on the label and was seen in some but not all trial sheep administered Flexolt. Four of the 15 trials were extended out to 287 days or more and three of the four trials achieved no live lice out to 287, 375 and 377 days. The fourth trial achieved 98.4% efficacy at 382 days, however there were no viable eggs, and it is believed to have been a recent infestation from a neighbour.

Map of Australia showing trial sites for Flexholt

Image 1. Location of Flexolt trial sites

Table of locations and wool lengths for trials

Table 1. Location and wool length at treatment of Flexolt trial sites

FLEXIBITY OF USE

Flexolt brings so much flexibility to producers for their lice control programs. Traditionally, shearing has been the only time during the management calendar that effective treatment and eradication of lice was possible, and only if split-shearing was not practiced. Shearing however, is a very busy period for producers, with labour and time in short supply. Flexolt offers producers a choice in their annual lice treatment program — treat at shearing or find another time. It means producers are no longer bound to shearing for effective lice control. This opens many timepoints across the farming calendar to help minimise common management challenges such as labour, weather, time, lambs at foot and split shearings.

Flexolt helps producers adapt to common challenges that can affect externally applied lice products. It is unaffected by rain, helping to minimise possible application delays. Importantly, lambs at foot* can be treated regardless of wool length and the odd poorly shorn sheep can be treated effectively without reinfesting the flock. Flexolt can also be used prior to lambing or as a pre-lambing treatment despite wool length, reducing the number of sheep that need to be treated.

Flexolt also reduces farm management challenges across the entire flock. Split shearing is common practice and often leads to lice outbreaks. This is because separately treated mobs have the potential to spread infestation between them throughout the year. Now, all management mobs can be treated at once regardless of wool length. While newly purchased sheep can be treated and quarantined from the rest of the flock, with no shearing required.

Due to its flexibility, Flexolt provides a unique opportunity for producer groups, management groups, local areas, or neighbours to work together to eradicate lice. Due to its efficacy in all wool lengths, all producers within the area or group can treat at the same time regardless of when their shearing happens. The ability to treat without having to manipulate management or shearing times greatly increases the likelihood of regional control programs to be undertaken and to be successful.

Image 2. Examples of Flexolt use throughout the normal animal health management calendar

APPLICATION

Flexolt is a low volume oral drench that is given at a dose rate of 1.5ml per 10kg of body weight. Flexolt can be administered through any oral drench gun, with a 9mm tubing between the pack and the applicator, as long as it has been well maintained and calibrated before use.

A representative sample of animals should be weighed before treatment. Dose the mob to the heaviest animal by body weight in each group (ewes, wethers, rams, lambs). Where there is a large variation in size within the group, dose rate should be based on the label directions for each weight range. Do not underdose. Drafting into two or more lines may be appropriate, to avoid excessive overdosing. It is essential that every sheep is treated to achieve lice control — it is recommended that as sheep are treated, they are marked so any untreated sheep can be identified and treated. Do not leave any sheep in the flock untreated.

Flexolt is safe for use in breeding rams and pregnant and lactating ewes, however, safety in ewes during mating has not been established. Flexolt has been shown to be safe at five times the maximum recommended dose rate (15 mg fluralaner per kg body weight) and safe for the treatment of young lambs as small as 6 kg body weight. Lice control is not affected by rainfall before or after treatment.

LICE ERADICATION PROGRAMS

Due to the inherent challenges in treating and eradicating lice, industry has traditionally described a three-year lice eradication plan. This allows three successive short wool lice treatments at shearing to work towards lice eradication. It also gives properties time to ensure that their biosecurity and quarantine processes are in place to reduce the risk of lice re-introduction after eradication is achieved. With the introduction of Flexolt there is the potential to condense a 3-year lice eradication program into a 12 to 18-month program. Flexolt allows for the possibility of two to three full flock treatments within a 12 to 18-month period, thus allowing eradication to be achieved quicker and minimising the impact of lice within the flock.

Image 3. Examples of lice eradications plans with and without using Flexolt^®

GOLDEN RULES OF LICE CONTROL

In order for the full effectiveness of Flexolt or any lice control product to be realised and for lice eradication to be achieved, the golden rules of lice control must still be practiced.

Treat all sheep at the one time.

All sheep must be treated at the same time. This includes lambs, ewes, wethers, rams, killers, poddies, and shedding sheep.
Clean musters must be achieved.
If ewes have lambs at foot at treatment both ewes and lambs must be treated.
If treating sheep pre-lambing ensure the selected product is applied early enough (follow label instructions) to allow all lice to be controlled before lambing commences, or live lice can persist and infest lambs.
Flexolt gives you the option to treat all sheep at the same time if split-shearing occurs on farm.

Sheep are weighed to ensure accurate dosing.

Determine accurate body weights using scales. Dose to the heaviest animal in each group (ewes, lambs, weaners, wethers & rams).
Incorrect dosing can have a significant impact on the efficacy of treatments.
If weigh scales are not used an accurate assessment of body weight is required.

Correct application of lice control products.

Follow label instructions on the correct application of products i.e. placement of backliners.
If using backliners or dips, ensure all sheep are cleanly shorn. Poorly shorn sheep or sheep with cotted wool or dermo can reduce the efficacy of backliners and dip.
The efficacy of Flexolt is not affected by poorly shorn sheep or cotted wool.
Use the correct applicator for the product being used.
Ensure all applicators are serviced and calibrated before treatment and regularly during use.
During treatment ensure that each sheep is clearly identified as being treated. For Flexolt this means using a crayon, marker, or spray to identify treated sheep while working.
One missed sheep can mean the failure of a lice eradication program.

Do not mix treated and untreated sheep.

Some lice products claim a period of protection against reinfestation. Despite these claims it is unwise to rely on chemical treatments to protect sheep from becoming infested. It is best practice to manage mobs so that treated and untreated sheep do not contact each other.

Quarantine and biosecurity.

A good biosecurity plan must assume that introduced sheep are infested with lice regardless of their history or whether there are no lice detected or signs of lice.
Ensure fencing is stock-proof. This includes boundary and internal fencing.
Stray sheep and sheep straying between mobs present a high risk for lice introduction and spread.
All bought-in or agisted sheep should be treated and quarantined for lice.
Understand all introductions present a risk for introducing lice, this includes rams. Rams should be treated and quarantined for lice on introduction.
Flexolt gives you the option to conduct a quarantine treatment without the need to shear first.
Remember a new lice infestation may take 3-6 months before signs of lice are evident. If stock are not treated for lice on introduction, they must be quarantined long enough for an infestation to become evident, or until they can be treated with the whole flock.

Conclusion

Every sheep flock is likely to have a lice outbreak at some point and many have been struggling to control and eradicate lice for years. Flexolt gives producers more control over the way they manage lice. This innovative product will help make on-farm processes more efficient and reduce the impact of sheep lice on flocks across Australia.

* Lambs from 6kg body weight

References

Data on file. MSD Animal Health.