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Sequential treatments more successful against resistant sea lice


February 4, 2015
By John Nickum

MSD Animal Health (known as Merck Animal Health in the USA and Canada) recently presented results from a research study assessing the benefits of treating salmon with emamectin benzoate (SLICE®) followed by hydrogen peroxide.

The presentation, at the 10th International Sea Lice Conference in Portland Maine August 31 – September 5, 2014, described the study and results that found sequential treatment provided clearance of existing sea lice infections and reduced re-settlement of an emamectin benzoate-resistant sea lice strain more effectively than treatment with hydrogen peroxide alone.

The study included 28 treatment tanks of Atlantic salmon randomly assigned to 14 treatment groups with 10 groups receiving SLICE from day 0 to day 6.  Nine of these groups were also treated with hydrogen peroxide at concentrations 600, 1000 and 1400ppm administered at either 3, 7 or 12 days after the end of the SLICE treatment.  The presentation highlighted the greater effect against sea lice infection when hydrogen peroxide was administered 7 or 12 days after SLICE in a concentration of 1000 or 1400ppm. Hydrogen peroxide treatment 7 days after SLICE had 86.1% efficacy at 1000ppm and 81.8% at 1400ppm. Treatment 12 days after SLICE had 83% and 91.2% efficacy at 1000 and 14000ppm.

“Sequential treatment with SLICE and hydrogen peroxide has been adopted by a number of veterinarians and producers to improve sea lice control, particularly in populations that have shown resistance to the treatments,” said Dafydd Morris, MSD Animal Health.  “We are pleased to present this important research to help producers optimize their sequential treatment approach…”


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