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Does your lice treatment work?


Lice are cunning parasites. They can survive on animals using tactics developed over thousands of years. To outsmart them, we need to understand their biology, their life cycle and also their incredible ability to develop resistance to common chemicals.

Fig 1: Sheep with fleece derangement, rubbing and pulled wool due to sheep lice
Fig 1: Sheep with fleece derangement, rubbing and pulled wool due to sheep lice

Sheep

There’s an old song that’s been sung many times in woolsheds and yards around Australia. It goes like this (to the tune of ‘Living next door to Alice’ by Smokey)

“The neighbour’s sheep, got through the fence

Ate all my grass, but they don’t pay no rent

And the worst thing about it is, they’ve got sheep lice

Now my sheep have got it, and there’s wool on the trees

They’re scratching just like a dog that’s got fleas

And the wool is for shearing not pulling. It just makes my blood freeze!

I know just how they come here, I hope they’re gonna go

There must be a solution but I sure as hell don’t know,

‘Cos for twenty four years, I’ve been living next door to sheep lice

Showers, dips, chemicals, I pour on twice a year

Got so much in my system that I feel a little queer

But I’ve got to find a way to stop living next door to sheep lice!”

 

We know from research studies that sheep lice don’t always come from the neighbour’s place. In fact, many lice are surviving treatments from one year to the next because of inadequate application methods or because they have developed resistance to the chemicals used. The good news is that the LiceBoss Product Search Tool tells us which lousicide chemicals work and which ones don’t. Note that combination products are also available.

High levels of resistance

Insect Growth Regulators- including the once popular active ingredients such as diflubenzuron and triflumuron

Synthetic Pyrethroids- including deltamethrin and cypermethrin

No or very little resistance detected

Neo-nicotinoids – including imidacloprid and thiacloprid

Organophosphates – including diazinon and temephos

Spinosad – in the product Extinosad

Macrocyclic Lactones (MLs, mectins) including ivermectin and abamectin

Fig. 2: Cow with rubbing lesions from lice
Fig. 2: Cow with rubbing lesions from lice

Cattle

With cooling weather and cattle growing longer winter coats, lice numbers are increasing.

Reports from the field in recent years have indicated that lice are surviving treatments with the popular pour-on or injectable mectins (Macrocyclic Lactones, MLs). This appears to occur with both sucking and biting lice. As yet unconfirmed by published research trials, the reports are concerning because these products are currently the most common way that producers treat cattle for lice.

These reports suggest resistance, but may only be ‘treatment failure’, because:

  1. injectable ML products do not have a full control claim for biting lice and
  2. the application of pour-on products may not always be adequate to reach all parts of every animal’s body.

However, cases of biting lice resistant to deltamethrin (a synthetic pyrethroid pour-on used commonly in Australia) have been confirmed in Ireland.

Note that even if only a few lice survive on one animal, the lice will then breed and re-infest the whole herd.

Fig 3: A nest of biting lice and nits (lice eggs) in the switch of the tail in an infested beast
Fig 3: A nest of biting lice and nits (lice eggs) in the switch of the tail in an infested beast

Alternative treatment options for lice can be seen on the Cattle LiceBoss Treatments page. They include:

  1. Insect Growth Regulators
  2. Synthetic Pyrethroids (no resistance reported in Australia)
  3. Organophosphates

With cattle lice, it is also important to diagnose whether the infestation is caused by sucking or biting lice, or both. As mentioned above, biting lice are harder to eradicate using injectable treatments, while sucking lice have had resistance reported overseas. Send some lice in a sealed jar to your veterinary parasitology lab for identification.

Summary

Check LiceBoss to choose the treatment most likely to eradicate lice in your stock.