Seresto flea and tick collar for large dogs works through contact, so fleas and ticks do not have to bite your dog to die. It is convenient, odorless non-greasy collar; No need for messy monthly treatments. Starts to repel and kill fleas within 24 hours of initial application. Flumethrin 4.5% Imidacloprid 10.0% Other ingredients 85.5% Trans Z-1/trans Z-2 Ratio: max 66% trans Z-1 and min 34% trans Z-2.
