I have never dewormed my rabbits. I know some places do once or twice a year. There is a paste called Panacur, but it is made for horses and has to be adjusted in dose for rabbits. I am not comfortable giving such medicine to my rabbits. There are also different kinds of worms, so you could treat for one type and they could have the other. I would keep on eye on the rabbit feces and if something looks strange take a sample to a vet.