A mongrel, mutt or mixed-breed dog is a dog that does
not belong to one officially recognized breed and including those that
are the result of intentional breeding. Although the term mixed-breed
dog is sometimes preferred, many mongrels have no known purebred
ancestors. Crossbreed dogs, and designer dog, while
also a mix of breeds, differ from mongrels in being intentionally bred.
At other times, the word mongrel has been applied to informally
purpose-bred dogs such as curs, which were created at least in part from
mongrels, especially if the breed is not officially recognized.
Although mongrels are viewed as of less
commercial value than intentionally
bred dogs , they are thought to be less
susceptible to
genetic health problems associated with
inbreeding (based on the theory of heterosis), and have enthusiasts
and defenders who prefer them to intentionally bred dogs. Estimates
place the prevalence of mongrels at
150 million animals worldwide.