That is *not* correct, where did you read that? To de-worm correctly you need to know what worms you are treating and the best way to do this is to have *routine* fecals done.
Ivermectin is not an effective poultry de-wormer. It might treat large roundworms, and maybe cecal worms, but does not treat capillary worms, gape worms, or tape worms.
Fenbendazole (Safeguard & Panacur) treats large roundworms, cecal worms, capillary worms, gape worms, and possibly some species of tape worms, though praziquantel is the better choice for tapes. Capillary worms and gapeworms require 5 day treatment.
Albendazole (Valbazen) treats large roundworms, cecal worms, capillary worms, gape worms, and possibly some species of tape worms, though praziquantel is the better choice for tapes. Gape worms require 3 day treatment.