Why not just test the stools and treat when the test shows parasites?
Testing stool samples for parasite eggs should be done routinely, every couple of months when your pet is young, and at least annually when they are an adult.
However, on some days the worms produce few eggs, or in many cases the worms are too young to produce eggs. In these situations, we may not find evidence of infection microscopically. Stool samples, therefore, do not demonstrate the presence of parasites 100% of the time.
We do not always depend on a negative stool sample. We include many factors before making a conclusion.