Street dogs in Greece.

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In one landmark study, the effect of breed on longevity in the pet dog was analyzed using mortality data from 23,535 pet dogs. The data were obtained from North American veterinary teaching hospitals. The median age at death was determined for pure and mixed breed dogs of different body weights. Within each body weight category, the median age at death was lower for pure breed dogs compared with mixed breed dogs. The median age at death was "8.5 years for all mixed breed dogs, and 6.7 years for all pure breed dogs" in the study.

In 2013, a study found that mixed breeds live on average 1.2 years longer than pure breeds, and that increasing body-weight was negatively correlated with longevity (i.e. the heavier the dog the less its lifespan).

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Mixed-breed dog.

A mixed-breed dog is a dog whose ancestry is generally unknown and that has characteristics of two or more types of breeds. A mixed-breed may be a crossbreed dog, a random-bred dog, or a descendant of feral or pariah dog populations. "Random-bred" is a genetic term meaning an animal, population, or breed that was bred or developed without planned intervention of humans and whose ancestry and genetic makeup is generally not known.

When the term mixed-breed is used for populations of dogs with no purebred ancestors, it is technically a misnomer. The implication that such dogs must be a mix of defined breeds may stem from an inverted understanding of the origins of dog breeds. Pure breeds have been, for the most part, artificially created from random-bred populations by human selective breeding with the purpose of enhancing desired physical or temperamental characteristics. Dogs that are not purebred are not necessarily a mix of such defined breeds. The term crossbreed refers to dogs produced by a breeding of two different purebred dog breeds.

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From Wikipedia, the free encyclopedia.

Mongrels in Athens.

Athens map.