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.
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
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:
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.
Alternative treatment options for lice can be seen on the Cattle LiceBoss Treatments page. They include:
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.
Check LiceBoss to choose the treatment most likely to eradicate lice in your stock.