Don't let lice win
Why inaction is costing you and your neighbours

Lice in sheep aren't just a minor nuisance; they're a shared threat to flock health, wool quality, and farm profitability. Yet, some farmers are still not treating lice effectively, or at all. This inaction doesn't just harm one property; it compromises the effectiveness of treatments across entire districts and imposes costs on responsible neighbours.

When one farm neglects proper lice control, it becomes a reservoir of infestation, constantly reinfecting nearby properties. These repeated reinfestations mean more frequent treatments, higher labour and chemical costs, and, most critically, a faster path to chemical resistance.

One class of lice treatment under threat is the benzoyl phenyl ureas (BPUs), such as diflubenzuron and triflumuron. These insect growth regulators (IGRs) work by inhibiting chitin synthesis, preventing louse nymphs from developing properly and disrupting egg hatching. They are valuable tools because of their safety profile and broad insect activity, but they do not kill adult lice. That means correct timing and thorough application are essential.

However, overuse, poor application, and constant reinfection, often due to untreated neighbouring flocks, accelerate resistance. In Australia, resistance to both triflumuron and diflubenzuron has become so widespread that these treatments have largely been abandoned. In New Zealand, early signs of resistance have already been observed in blowfly populations, and lice resistance may not be far behind. Unfortunately, there is no independent science base in New Zealand actively looking at insecticide resistance in either blowflies or lice.

Resistance results in product failure, meaning lice persist even after treatment, and viable alternatives may be limited, more expensive, or more harmful to the environment. A reduction in persistent activity is an indication of developing resistance, while poor application and sub-lethal dosing are suspected to encourage resistance development.

The bottom line: failing to treat lice, or treating them poorly, isn’t just your problem. It becomes everyone’s problem. The cost isn’t just the wasted product or time; it’s ongoing reinfestation, resistance, and long-term control difficulties.

What Can You Do?

• Treat lice at the right time and correctly. Follow product label instructions carefully, and book a lice consultation plan with one of our team.
• Communicate with neighbouring farms to coordinate treatment and prevent reinfestation.
• Avoid repeated use of the same active ingredients, especially those with known resistance risks like BPUs.
• Monitor lice levels regularly and seek veterinary advice if control seems ineffective.

In short, being proactive about lice control protects not just your flock, but your neighbours’ and the entire industry. Don’t let poor practice become the reason we lose yet another effective tool.

Nicola Johns
AHVS Sales Team Leader
North Canterbury Veterinary Clinics Ltd
027 436 0484
nicolaj@ncvets.co.nz

We're loyal, not just local.

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