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prevent_sheep_lice_resistance

Sheep lice continue to cause an issue for wool producers but producers continue to benefit from a number of effective sheep lousicides. The most recent survey1 has found that the prevalence of lice has decreased in recent times, with producers reporting no evidence of lice in 70% flocks in 2018, compared to 59% of flocks in 2011. The good news is that effective treatments continue to be available to control lice, so the prevalence of lice is expected to remain stable.


While sheep producers currently benefit from a number of effective sheep lousicides, past history shows that this hasn’t always been the case. Stepping back to the 1980’s, sheep lice developed resistance to the once highly effective synthetic pyrethroids (SP) and new chemicals were required. Insect growth regulators were the next class of lousicide to be used, and followed a similar trajectory to the SP’s with significant lice resistance developing in less than 10 years of being on the market2. While improved biosecurity and proper treatment application will help reduce lice infestations, more than 70% of flocks require regular chemical treatment for lice control1. Chemical resistance in lice is expected to increase with the continued use of the same chemicals3.

While there is no known resistance to the commonly used sheep lice actives available today, including imidacloprid, abamectin and spinosad, the question is how long we can expect these to work into the future? Past experience suggests that this is a real risk. One approach proposed to delay the onset of parasite resistance is to adopt the use of combination products. By using 2 or more actives with different modes of action, it is more difficult for the parasite to develop resistance to multiple actives. This approach has been used quite successfully for worm control, and is now becoming available for treatment and management of sheep lice.

FENNEC Pour-On for Sheep is the first dual active combination lousicide to be developed, combining the highly effective actives imidacloprid and abamectin in an easy flow pour-on formulation. FENNEC offers a good option to use a highly effective product while introducing product stewardship principals into the lice control market that may extend the duration of efficacy of important active ingredients into the future.