Viper contains thiacloprid which has a unique mode of action that provides rapid knockdown control of lice.² Viper continues to kill adult lice and emerging nymphs for 4 weeks after treatment when applied within 24 hours of shearing. Viper can be applied up to 7 days after shearing or to unshorn lambs from two weeks to two months of age. Elanco offer a 6 month off shears lice free guarantee. Key Product Benefits: Highly potent, second generation neonicotinoid chemistry 1,2,3 4 weeks? protection when applied within 24 hours of shearing Flexible off-shears application ? up to 7 days 6 months off shears lice free guarantee