depends on if your feeding them after freezing or feeding fresh, if from frozen just stick to your usual worming routine,although nobody has explained to me where the idea of the 3 week time scale to kill worms came from, i don't leave them that long and never had any bother. from fresh you'll need to worm more often but for the price of a couple of drontal tabs, i've no problem with feeding whole carcess fresh rabbit myself, though most will disagree.