Disease prevention, vaccinations, routine healthcare is probably where most of the income is generated. Surgery can be a source of income. The sale of healthcare products: flea products, heartworm preventions, even prescription dog foods is another source of income. Probably the thing that you get least for your time is in diagnostic and treating sick animals, as far as your percentage of time you spend with an animal, compared to what you do with the routine things: the vaccinations and healthcare¦But, those are your areas where you make money.