Hookworms can cause bloody stools, whipworms can cause pale nasty smelling soft stools. The ivermectin in Heartgard only affects certain types of worms, the others have developed resistance to it, same with some of the regular wormers. It is important that you actually know what you are deworming for so that you use the right product.
There are a few things that fecal floats are not good at detecting, so once a year I have a fecal sent to the lab for analysis. It costs around $20. I haven’t needed one of my dogs wormed in several years, except for new puppies with roundworms. However, one of my cats needs deworming regularly. She has feline herpes and so already has a challenged immune system.
