Old Dog Disease
Diseases get more common with age. Tartar and loss of teeth, arthritis, heart disease, liver and kidney complications and almost any kind of cancer are typical problems in an old dog's life. You could say that a dog that is more than 10 years old will probably visit the vet for more than vaccination. It is possible now to find a solution for all of these problems, even cancer. But eventually a tie arrives when medicine and science can do nothing to help a dog, and the most sensible choice is to end the dog's life so it does not suffer anymore. The dog will not feel anything and will fall asleep. Giving your dog a peaceful painless death is a debt you have with your pet after many years of loyalty and friendship. You must be with your dog when this moment arrives.
Planning offspring and motivating crossbreeding.
The owner of a cross or mixed breed dog is not a classic breeder: they are not trying to get typical representations of what a dog "should be".
But, as much as you wish your dog to immortalize itself in little pups, you must consider the probability of finding homes for several puppies which won't have economical value whatsoever. A bitch usually gives birth to 6 pups, and you must make sure they don't end up in a shelter.