Any human food is not ideal dog food. Specialised dog foods are the best way to cater for your canine's idea nutritional needs. However, if your dog accidentally eats a small amount of ketchup it shouldn't do him or her any harm unless it were to trigger an allergic reaction (which is unlikely, but possible). Like many human foods, ketchup is very high in sugar which is definitely not a good addition to any dog's diet particularly because it is so difficult to keep a dog's teeth clean even when they're eating a good, healthy diet of only dog food and dog treats.
