The disadvantages of a mixed breed outweigh the advantages for many families. The sire of the litter often hits and runs, and the owners of the dam know little or nothing about his size, type, breed, health, or temperament. Indeed, a mixed breed dog that is not protected during her fertile period can be bred by several dogs, producing a litter with two or more sires. Thus puppy purchasers know almost nothing about the pup except that he’s cute and loving.
Some mixed breeds, especially the small ones, exhibit the worst characteristics of both parents. Poodle mixes can be high-strung, even neurotic and terrier mixes can be destructive, stubborn, difficult to housetrain, and frantic. Mixes of medium or large breeds such as Chow Chows, Akitas, German Shepherds, Rottweilers, Doberman Pinschers, or any of the guard dogs can be dominant-aggressive, which can be especially difficult in families with small children or with an adult man or woman who has neither a commanding voice nor a confidant manner.
Another disadvantage of mixed breed dogs is the inability to predict the size, coat-type, or temperament of the adult dog from seeing a litter of puppies from an unknown sire or worse, from an unknown dam and sire. Animal shelter personnel can guess at the breed of an abandoned litter of pups, but they cannot really tell much by looking at a roly poly bundle of fur with the little round face and short legs. And even if the litter parents are known, if they are two widely divergent breeds or mixes in size, coat, or temperament, it will be difficult to determine which pups will take after Mom, which ones will resemble Dad, which ones will look and act like a little bit of both, and which ones will look and act like neither parent.
Mixed breed dogs are sometimes considered to be the “natural” dog, the epitome of dogdom if the purebred breeders had left domesticated canines alone instead of breeding for particular abilities and physical attributes. But some folks go a bit too far, claiming that mixed breeds suffer from few of the genetic health and temperament problems inherent in purebreds. It is true, that, left alone to reproduce naturally, purebred dogs would probably become homogenized into a prototypical pariah dog – about 45 pounds in weight, 18-20 inches tall, yellow or sable colored, with upright ears and a long, slightly curled tail – similar to the Dingo of Australia, Canaan Dog of Israel or Carolina Dogs of the Southeastern US. It is also true that if dogs ran free, the unhealthy ones would not have the stamina to compete, and so the gene pool would of necessity be healthy.
However, such a return to the wild is not going to happen, and in spite of assertions that they are healthier than purebreds, crossbred and mixed breed dogs are subject to the same diseases, structural problems, joint dysplasias, allergies, and genetic abnormalities as their blue-blooded cousins. Furthermore, it is more difficult to track diseases in crossbreeds and mixed breeds because these dogs are unlikely to be x-rayed for dysplasia, checked for abnormal thyroid or eye diseases, examined for heart problems, or tested for various autoimmune problems. For example, Golden Retriever-Collie crossbred puppies are susceptible to the diseases that affect the two breeds: hip dysplasia, heart abnormalities, eye problems, etc. The inheritance of structural problems such as hip dysplasia is complex and can multiply through the generations; thus mixed breed puppies in litters from crossbred or mixed breed parents are also potential victims.