Are PEDIGREE dogs less healthy

By Carol Beuchat PhD

Data from -

• BellumoriTP, TR Famula, DL Bannasch, JM Belanger, & AM Oberbauer 2013 Prevalence of inherited disorders among mixed-breed and purebred dogs: 27,254 cases (1995-2010). J Am Vet Med Assoc 242: 1549-1555.(pdf)

Much ink has been spilled arguing about the health of mixed breed and purebred dogs. I haven't traced the history of this debate, but I imagine it has been fueled by two issues: first, the high burden of genetic disorders in purebred dogs, and second by the sentiment of some that people should adopt shelter dogs instead of purchasing a purebred. The argument from one side is that mixed breed dogs are healthier than purebreds, and this is rebutted by purebred breeders as a fallacy.What makes this complicated is that there are many purebred dogs that live long, happy lives, and others that do suffer from an inherited disorder, and of course the same can be said of the mutt of mixed heritage. To get beyond the anecdotes, what we need are data, and a recent study provides them.The study by Bellumori et al (2013) used medical records from the veterinary clinic at UC Davis for more than 27,000 dogs and compared the incidence of 24 genetic disorders in mixed versus purebred dogs. The abstract of the paper is included at the bottom of this page.Here is what they found:1) The incidence of 10 genetic disorders (42%) was significantly greater in purebred dogs.2) The incidence of 1 disorder (ruptured cranial cruciate ligament; 4%) was greater in mixed breed dogs.3) For the rest of the disorders examined, they found no difference in incidence between mixed and purebred dogs.

(Note that they indicate subclassifications of epilepsy but counted it as a single disorder in the list of 24.)The data in the study are presented as a mean odds ratio (OR) comparing purebred to mixed breed dogs. An equal risk for a disorder in purebred and mixed breed dogs would have an OR = 1. To make the data easier to visualize, I have computed (OR* = 1-OR), for which equal risk in purebred and mixed breeds dogs would have a value of 0, and higher odds for purebreds would have OR* > 0, and higher odds for mixed breeds would have OR* < 0. Therefore, in the graph below, positive values (above the horizontal line) indicate that the odds risk is greater for purebreds, and negative values indicate greater risk for mixed breeds.Asterisks (*) on bars indicate that in 50 comparisons of affected dogs with matched control sampling sets, there was a significant probability(p < 0.05; i.e., less than 5%)that pure and mixed breed dogs differed in expression of the condition. (SeeMethods and Materials: Statistical Analysisin Bellumori et al 2013 for details.)

Again, for 10 of the genetic disorders, risk was significantly higher in purebreds, and for one (cruciate ligament rupture) it was greater in mixed breed dogs.An interesting thing to note is that with the exception of one disorder, patent ductus arterioles, the odds ratios are higher for purebreds, but these failed to meet the criterion for statistical significance (hence no asterisk). This does not mean that the incidence in purebreds and mixed breeds was the same, only that they failed to find a statically significant difference in this study. This might be because they had inadequate data to detect a difference, or that in fact purebred and mixed breed dogs are the same and the differences in these data can simply be an artifact of sampling. (They incidentally found a significantly higher risk of being hit by a car in mixed breed dogs, which of course is not a health disorder and presumably not genetic.)

For the 10 genetic disorders which were significantly more prevalent in purebred dogs, I have created graphs that include the 5 breeds with the highest rates of affected dogs plus the value for mixed breeds.

This study concluded that purebred dogs have a higher risk of at least 10 of the 24 genetic disorders examined.

Nevertheless, the findings of this study in the lay press and among purebred fanciers were not so clearly expressed. Some examples:

• "It has been publicly discussed for years that hereditary disorders would be a direct consequenceof the strict selective breeding of pedigree dogs and that for this reason the purebreds would have a much greater risk of developing hereditary disorders than mixed breed dogs. According to the latest research by Bellumori and his group, this assumption does not seem to hold. Indeed many diseases seem to be as common in mixed breed as in pedigree dogs" (Moller, on the MyDogDNA website; pdf)

• "A new study on the prevalence of inherited disorders among American mixed breed and purebred dogs has negated the common assumption that a mixed breed dog is always healthier than a purebred dog" (Quickfall 2013).

• "A new study by researchers at the University of California, Davis, indicates that mixed breeds dont necessarily have an advantage when it comes to inherited canine disorders." UC Davis press release

Unless you examine the study, these statements would all leave you to believe that the study demonstrates that purebred dogs are "just as healthy" as mixed breed dogs. But there is some careful parsing of language in each of them - "A new study...has negated the common assumption that a mixed breed dog is ALWAYS healthier" (emphasis mine). Okay, fair enough. Mixed breed dogs have more ruptured cruciate ligaments.And another hedge: "mixed breeds don't necessarily(emphasis mine)have an advantage when it comes to inherited canine disorders." This would seem to be saying that the default argument is that mixed breeds are healthier, usually but not necessarily, whatever that means. So indeed, "this assumption does not seem to hold", but for nearly half the disorders examined here the mixed breeds came out on top.This study found that purebred dogs have a significantly greater risk of developing many of the hereditary disorders examined in this study.No, mixed breed dogs are not ALWAYS healthier than purebreds; and also, purebreds are not "as healthy" as mixed breed dogs.The results of this study will surprise nobody who understands the basics of Mendelian inheritance. Breeding related animals increases the expression of genetic disorders caused by recessive mutations, and it also increases the probability of producing offspring that will inherit the assortment of genes responsible for a polygenic disorder.The authors of this study tackled a very important question that is difficult to address because collecting the "perfect" data set is impossible. Using data on clinical occurrence of disease is fraught with difficulty because of many sources of potential complication - perhaps purebred dogs are more likely to receive veterinary treatment than mixed breeds, and comparisons among groups (e.g., afflicted vs not, purebred vs mixed) are confounded by unequal sample sizes or differences among groups in the age, sex, etc of animals. It's a statistician's nightmare. (In fact, a highly regarded statistician, Thomas Famula, was involved in the study.)In fact, the "perfect" comparison will never be done. But this study presents a large compilation of data and a thorough analysis that is the first (and might be the only) attempt to explore differences in predisposition to disease in purebred and mixed breed dogs.

• Moller F Mixed breed dogs are not protected from breed disease heritage. MyDogDNA website.(pdf)
• Quickfall L 2013 Kennel Club welcomes study looking at health of all dogs. Dog News, Vol 29(30): 134, July 26, 2013. http://issuu.com/dognews/docs/072613/134
• UC Davis press release (4/2/2014) Purebred dogs not always at higher risk for genetic disorders, study finds.(pdf)
• Wood R 2013 Prevalence of genetic disorders compared in purebred and mixed-breed dogs. CABI VetMed Resource. http://www.cabi.org/VetMedResource/news/23088

This is the abstract from the publication:

Pedigree Dog Health

Dogs come in all shapes and sizes. Sadly, some dogs are more likely to get ill or have problems, simply because of their breed. Pedigree dogs are most likely to have these problems as they are more closely bred than other dogs.

Wed always recommend thinking very carefully before you buy a pedigree dog. Its a good idea to read up about the breed youre thinking of getting and finding out about any health problems that could crop up later in their life.

If youre thinking about getting a pedigree dog, visit our dog breeds pages where weve put together information about each breed of dog.

What is a Pedigree dog?

If your puppys parents are the same breed of dog, your puppy is a pure breed, but not necessarily a pedigree. A pedigree dog will have parents who are the same breed but they will also be eligible for registration under a pedigree scheme. There are a few schemes but the Kennel Club registration scheme is the most well known.

If your dogs parents were two different breed they will be a cross breed. A mix of three of more breeds makes your dog a mixed breed (eg. if one parent is a cross breed and the other parent is a different breed). Mixed breed dogs are less likely to have serious, breed-related health problems than pedigree dogs.

The problem with pedigree

Over thousands of years, humans have bred dogs to look or behave in a certain way. For some dogs this means that their features have become exaggerated, like flat-face on a Pug or the wrinkly skin of a Shar Pei. Unfortunately, some of these changes to the way they look have caused serious health issues.

Exaggerated features that can cause serious health problems include:

• Long backs (e.g. Dachshund). These dogs are likely to suffer from painful disc problems affecting their spine.
• Short legs (e.g. Corgi). This is caused by a form of dwarfism which makes arthritis likely.
• Sloping backs (e.g. German Shepherd). This makes lower back, hip and knee problems more likely.
• Extreme size (e.g. Great Dane). These dogs are more likely to suffer from heart disease, bone and joint problems. Theyre likely to have a shorter lifespan.
• Very small size (e.g. Chihuahua) These dogs can have fragile bones and poor dental health, as well as hip and knee problems.
• Wrinkly or excessive skin (e.g. Shar Pei). Wrinkly faces mean that these dogs can struggle to communicate using normal facial expressions. The folds of skin are also prone to infections.
• Very small ears (e.g. Shar Pei) The inside of the ear is incredibly narrow meaning ear infections are more likely.
• Very large ears (e.g. Basset Hound). The inside of the ear can get very moist which makes ear infections more likely. These long ears can easily be accidentally trodden on which is very painful for the poor dog!
• Droopy eyelids (e.g. Bloodhounds). These make eye infections more likely and these dogs sometimes produce too many tears which can cause soreness around their eyes.
• Very large heads (e.g. Bulldogs) The puppys large heads make natural births very difficult and lots of litters have to be born by caesarean section.
• Small heads (e.g. Cavalier King Charles Spaniel). A smaller skull puts pressure on the brain causing severe pain and sensitivity in head and neck (called Syringomyelia). Flat faces (e.g. Pug, Bulldog, French Bulldog). These dogs have squashed noses which causes breathing difficulties. The shape of their skull means their eyes often bulge out of the eye sockets. They often struggle in hot weather and with exercise.
• Lack of fur (e.g. Chinese Crested). These dogs have difficulty controlling their body temperature and often have skin problems.
• Too much fur (e.g. Hungarian Puli). All that extra fur means these dogs are more likely to overheat, especially in centrally heated houses. Extra hair on their face can also make it difficult for them to see properly.
• Domed heads (e.g. Chihuahua). Theyre more likely to suffer from a brain condition called hydrocephalus.
• Very short tails. Short tails can lead to problems with the spine. It also stops the dog from communicating naturally with its tail.
• Cork Screw tails (e.g. Pug, Bulldog). These dogs can suffer from Spina Bifida (where the bones of the spine dont form properly) and other back problems. It also stops the dog from communicating naturally with its tail.

These issues can be very painful for your dog and can even put their life in danger. Treatment might mean your pet needs an operation which is difficult for both you and your dog. Managing these lifelong conditions can also be really expensive which can come as a shock to owners who werent expecting their pet to need treatment.

If youre thinking about buying one of these dogs, speak to your vet first to find out more about the conditions they might face.

Problem Breeds

Some breeds are so much more likely to suffer from health problems that theyve been classed as Category Three breeds by the Kennel Club. This means they face serious health problems that owners need to be aware of and prepared for. These breeds are:

Other dogs not on this list also have breed-related health problems, so its important to do your research before committing to getting a certain breed of dog.

Healthier pedigrees

If youre thinking of buying one of these breeds of dogs there are some steps you can take to make sure your dog is as healthy as possible.

First of all, choose a breeder who has health tested your puppys parents. This health test will show if the parents have any problems they might pass on to their puppies.

You can also look at the parents and the puppy for any signs of health problems. Check that:

• They can breathe normally and have no signs of breathing problems, like heavy panting or snorting.
• Muzzles of flat-faced dogs should be as long as possible.
• They are bright and responsive to you.
• They dont have lots of loose skin on their face, head or body.
• There is no evidence skin disease, such as rashes or sores. Check any skin folds, too.
• Their eyes are in a normal position, are a normal shape and they can blink properly.
• Eyelids shouldnt be too droopy and there shouldnt be lots of tear staining or wetness around the eyes.
• Their ears are not overly long.
• Their body and skin are high enough off the ground because they dont have tiny legs.
• They can walk normally and their joints look normal.
• Their teeth bite together correctly and their lips are in a normal position over their teeth.
• They do not have a nervous temperament.
• They are not overweight.

Help for pedigree pets

If youre worried your dog could be displaying any of these problems or youre thinking about getting a pedigree dog and want more information, speak to your vet. Theyll be able to give you more information about these potential health problems.

Find out if youre eligible for PDSA Vet Care.