A report has found that lice on cattle are developing resistance to pour-ons and other forms of insecticide used by farmers.
Some 17 beef farms with collectively over 600 cattle were used as part of the study for the report, with lice detected on 94% of the herds.
Two species of lice were identified, the chewing louse Bovicola bovis and the sucking louse Linognathus vituli.
The report said: “88% of infected animals were infested only with B. bovis and 5% only with L. vituli.
"Mixed infestations of both B. bovis and L. vituli were found in 7% of animals.”
Farmers are aware of the stress intense lice infestations can cause animals and usually blanket-treat animals at certain times of the year.
The report was entitled A pilot study on the prevalence of lice in Irish beef cattle and the first Irish report of deltamethrin tolerance in Bovicola bovis.
It looked at the use of deltamethrin based pour-ons. Deltamethrin is included in pour-ons such as Spot On, Animec and Butox.
Four farms were found to have lice that were resistant to the product.
“On day 20 post-treatment with a deltamethrin-based pour-on, 88% of animals were positive for lice and on day 27 post-treatment, 91% of animals were positive.
"On this date (day 27), the farm manager treated all animals a second time using the same deltamethrin-based product as used previously on day 0.
"On day 21 (21 days after the second louse treatment), lice were present on 62% of animals,” the report said.
Other types of products were also trialled that included acetone, deltamethrin and tea tree oil.
It was noted that there was a difficulty in applying pour-on uniformly to animals’ coats and this could impact the efficacy of the insecticide, but, overall, the report pointed to a global trend where lice are becoming resistant to some forms of insecticide.
It also pointed out that more work needed to be done on looking at non-chemical remedies and ensuring that cattle were not overcrowded during winter housing.