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A National Census of Mixed Breed Dogs

Data on the number and ancestry of mutts in America.

Although there is a lot of data about the number and distribution of purebred dogs in North America such data has not been available for mixed breed dogs. This is despite the fact that so-called "mutts" make up 53% of all of the dogs in the United States. There are reasons why we lack information about the makeup of mixed breeds with one of the most important being that it is often difficult to judge which breeds have gone into a particular dog based on the way that that animal looks alone. For example, if you had a cross between a poodle and a beagle, some of the offspring might appear to be beagles, others poodles, and some a strange mixture of the two. Furthermore, the owner's knowledge about the ancestry of his lovable mutt is often limited, and even if known it could be difficult to sort out if one or more of his parents were also mixed breed dogs.

dog canine mixed breed mongrel mut pet

A combination of scientific developments has now made it possible to get the data about the parentage of mixed breed dogs. First, the canine genome (the map of the DNA of dogs), including specific markers that identify particular breeds, has been worked out. Second, low cost kits which allow people to get a DNA sample of their dog at home and send it off for analysis are now available. This allows researchers to investigate the genetic background of our population of mixed breed dogs.

The data have now been analyzed from a national survey taken in 2010. The research team was headed by Dr. Angela Hughes, Veterinary Genetics Research Manager at Mars Veterinary (a company that produces kits for home sampling of a dog's DNA). They conducted the "National Mutt Census" for which they distributed more than 36,000 kits to owners of mixed breed dogs. These samples underwent genetic analysis by the Mars Veterinary team to determine the breed history of each dog. This genetic data was combined with more than 16,000 responses to a Web survey from mixed breed owners.

The first surprise in their results was that the mixed breed dogs which are pets tend to be small to medium size. Only 11% of the mixed breed dogs were 80 pounds or heavier.

The simplest guess as to the distribution of breeds which make up the genetic basis of the continent's mutts would be that the dog breeds that are most popular would likely be most likely to parent mixed breed offspring. This is a simple statistical assumption since the most commonly found dogs in a population are most likely the ones engaged in sexual trysts with other available dogs. There is some evidence for this in the data. For instance, the German Shepherd is the most common breed whose genes are found in mixed breeds, and in terms of its popularity, the American Kennel Club (AKC) ranks them as number 2. While German Shepherds prove popular as both a pure breed and as a component of mixed-breeds, the most common breeds registered by the AKC are not necessarily the most common breeds found in mixed breed dogs. The list of the top 10 most common breeds found in our mutts, along with their AKC ranking is shown below.

1. German Shepherd (No. 2 most popular AKC registered breed)

2. Labrador Retriever No.1 most popular AKC registered breed)

3. Chow Chow (No. 63 most popular AKC registered breed)

4. Boxer (No. 6 most popular AKC registered breed)

5. Rottweiler (No.13 most popular AKC registered breed)

6. Poodle (No.9 most popular AKC registered breed)

7. American Staffordshire Terrier (No. 70 most popular AKC registered breed)

8. Golden Retriever (No. 4 most popular AKC registered breed)

9. Cocker Spaniel (No. 23 most popular AKC registered breed)

10. Siberian Husky (No. 22 most popular AKC registered breed)

While one might be surprised that the Chow Chow ranks third in this group, despite the fact that it ranks 63rd in the AKC registrations, this really is understandable. It represents the past popularity of the breed since in the 1980s Chow Chows were extremely common and thus their DNA is commonly found as the grandparent or great-grandparent level in tested mixed-breed dogs. The case of the American Staffordshire Terrier is also quite interesting, since, their popularity seems to be rising despite the fact that their registrations with the kennel club appear to be dropping. This may well have to do with the fact that American Staffordshire Terriers are considered to be pit bulls, which as a group have a negative media image. Although they are not as popular with the dog fanciers who go to dog shows as they used to be, many people consider them to be good guard dogs. As a result unregistered American Staffordshire Terriers, or other mixed breeds that already have their genes in them, are being bred by average people as some form of protective measure for their homes (or their drug stash).

Although this data goes a long way toward determining the number and makeup of mixed breeds in North America it does not solve the ongoing debate about the relative merits of pedigreed versus mixed breed dogs. However there are a number of people who feel that the purebred strains have been weakened by too much inbreeding. Perhaps the rising preference for some of the "designer dogs", such as labradoodles, golden doodles and cockapoos is a reflection of this. The physician and genetic scientist, Michael Swift agrees saying "I prefer mutts. The artificial construction of the gene pool is bad for the species as a whole. In a restricted gene pool, the defects pile up. The truly superior specimen is the outbred, not the inbred."

Stanley Coren is the author of many books including: Born to Bark, The Modern Dog, Why Do Dogs Have Wet Noses? The Pawprints of History, How Dogs Think, How To Speak Dog, Why We Love the Dogs We Do, What Do Dogs Know? The Intelligence of Dogs, Why Does My Dog Act That Way? Understanding Dogs for Dummies, Sleep Thieves, The Left-hander Syndrome

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