Disadvantages of Mixed-Breed Dogs
While mixed-breed dogs have many advantages, they also have some disadvantages. Mixed breeds, especially puppies, can be less predictable than their purebred cousins, and it's possible, although much less likely, for them to experience some of the same health problems that purebred dogs experience. Dog owners shouldn't assume that adopting a mixed breed dog provides a health guarantee.
Mixed Breed Dogs are Less Predictable. The specific traits of mixed-breed dogs tend to be less predictable than purebred dogs. When you get a purebred puppy, you have a reasonable expectation within a narrow range of how large that puppy will grow to be as an adult. You can also expect certain behavioral characteristics if the parents are typical for their breed. While the specifics vary from breed to breed, getting a purebred puppy gives you a better idea of what specific traits to expect from the adult dog.
Mixed breed puppies provide no such expectations. Although most mixed breed dogs display 'average' dog traits because they are not bred to display specific any physical or behavioral characteristics, it is possible, although unlikely, a mixed-breed puppy could grow up to be a 10-pound dog, or it could grow up to be a 150-pound dog.
Additionally, the uncertainty isn't confined to physical characteristics. When you get a mixed-breed puppy, you have very little idea of how it might behave. Although you can hope for an average activity level, you don't know if the puppy is going to grow up to be a content, modestly active house dog, or a highly-active dog that requires hours of exercise every day. You also have no basis for determining whether your dog has inherited behaviors such as herding or guarding.
Getting an adult mixed breed dog (which allows you to see the adult and therefore more accurately determine the animal's temperament and behavior) negates some but not all of these disadvantages.