I was told every 3 months by CP when we rehomed our large tabby. Pets at Home told me every month if he's an outdoor cat that hunts and eats his kills regularly.
Anyone else heard this? He definitely eats birds, shrews, mice, moles, rabbits, pigeons etc on a regular basis. I don't want to leave him open to worms but I don't want to overdose him either!
(New rescue cat meanwhile has brought me nothing, nothing I tell you. Just hunts toys, leaves and small sticks but doesn't share them. A blessed relief)