Almost all puppies are born with intestinal parasites, which are passed from mother to pup during pregnancy. Although kittens are not infected when they’re born, they can become infected through their mother’s milk. Puppies can also become infected while they’re nursing.

Puppies and kittens should both be dewormed every 2 weeks, starting at about 2 weeks of age for puppies and 3 weeks of age for kittens. After the biweekly series of dewormings is finished, monthly deworming should begin (at about 8 to 9 weeks of age for kittens and 12 weeks of age for puppies).