More Australian sheep producers are rotating their lice treatments due to concerns about resistance, according to new industry research. Yet fewer producers reported resistance to lice control products in 2018 compared to 15 years earlier.
These lice treatment statistics were just some of the findings from a recently published Australian research paper that surveyed sheep producers from 2003 to 2019 to better understand the prevalence of sheep lice and trends in control practices. The study, published in the Veterinary Parasitology: Regional Studies and Reports Journal in January 2022, surveyed Australian sheep farmers in 2003, 2011, and 2018 to investigate a problem that was said to cost the Australian sheep industry $81 million a year in 2015.
Concerns about resistance to lice control treatments was an ongoing theme throughout the survey responses during the 15 years of research. The published paper highlighted findings that treatment failures may lead to increased resistance to lice control products.
“Failure to eradicate lice is often not due to resistance, but rather due to inadequate treatment or failure to treat every sheep on the property,” the report said.
“However, any treatment failure may expose lice to low levels of pesticide which may increase resistance in surviving lice, so rotation of products is recommended where lice have not been eradicated. If lice are eradicated, then the use of a different product the next time a treatment is used will not increase the risk of resistance to multiple products, since this will be a new infestation.”
According to this research, rotation of lice control treatments was the most important change to sheep management practices in 2018. This followed concern expressed in a similar 2011 survey about resistance to specific products and a wish to preserve the efficacy of current products. For example, in the 2018 survey, there was a 15 per cent increase in respondents who suspected resistance on their farm to neonicotinoids.
However, only 8 per cent of respondents reported suspected resistance to lice control products in 2018, down from a peak of 26 per cent in 2003.
Boehringer Ingelheim Cattle and Sheep Technical Manager Dr Gareth Kelly said survey results show how far the industry has progressed when it comes to preventing lice resistance. However, there were obviously some farmers who were still concerned about resistance to some lice control actives – specifically the newer actives. He said this highlighted the need for continued lice control strategies such as rotating treatments and the adoption of combination products.
“Farmers have been spoilt over the past decade with multiple actives to choose from when it comes to treating lice,” he said. “It’s easy to forget that resistance was once a problem – like when this survey first started in 2003 – and the industry has already lost two unique actives to lice resistance,” Dr Kelly said.
Biosecurity – lice infections from stray or purchased sheep – was the number one cause of recurring lice infestations in 2018, according to the sheep producers interviewed for this research.
Dr Kelly said farmers had long been advised of the benefits of treatment rotation in preventing chemical resistance, but it wasn’t until recently that Australian sheep producers had access to a lice treatment with two active ingredients formulated into a single pour-on product.
Boehringer Ingelheim’s Fennec Pour-On for Sheep is Australia’s first lice treatment that includes the active ingredients imidacloprid and abamectin. Both active ingredients cause paralysis of lice but do it in different ways.
Dr Kelly said this was the key to avoiding resistance.
“History has shown that sheep lice are highly capable of developing resistance to single active lousicides,” he said.
Fennec® Pour-On for Sheep.
“The use of combination products can decrease the chance of resistance building up because the two actives do not have a common resistance pathway. This is important as it is less likely that lice will develop resistance to either active when used together than to one of them alone, which in turn can slow the onset of resistance on a farm.”
This article was written by Boehringer Ingelheim for Seasons magazine.
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