how old do puppies need to be before testing for worms
Dogs that are already on heartworm preventive medication should also be tested periodically. The âprepatent periodâ for heartworm disease (the amount of time it takes for microfilariae to be produced) is approximately 6 months in a dog. During this time, heartworm tests will be negative even if a dog is actually infected. Therefore, puppies younger than 7 months old are generally not tested for heartworms. Instead, puppies should be started on heartworm preventive medication (usually during their puppy checkup visits) and tested when they are older than 7 months.