Loading the Dice for Defect, Deformity and Disease

Amy P. sent me a note about something she hoped I would address. She writes that she often hears people say:

"With an unknown mixed breed dog, who knows what kinds of problems are lurking there, and how many? At least with a purebred dog you know what problems you will be getting."

Ah, the old "better the devil you know than the devil you don't" case for Kennel Club dog ownership.

Too bad it's complete nonsense as far as canine health is concerned.

Just imagine someone telling you "Our family has hypertension, so we don't have to worry about cancer."

Eh?

Cancer and hypertension have nothing to do with each other!

If your family has a history of hypertension, you probably have the same chance of getting cancer as everyone else. And that chance is NOT zero!

Ditto for dogs.

If you own a breed with a seriously elevated chance of cancer, or a high incidence of epilepsy, that does NOT mean your dog will be free of heart disease, skin disease, liver disease, cataracts, or hip dysplasia.

Sorry, it does not work like that.

If you own a breed of dog with a particularly increased incidence of disease or defect, that negative health outcome is almost certainly ADDITIVE to the base of pathology which all dogs commonly face. One disease is not a "get out of jail card" for others diseases and congenital defects.

This is not to say that some genes are not linked.

A few are.

For example, we know that dogs with merle and spotted coats are more likely to be deaf than dogs with solid or big blocks of color on them.

That said, most diseases do not appear to be associated with linked genes. Those that are, are the exception rather than the rule.

In addition, when we do see linked genes, that link almost always points to an elevated incidence of something negative rather than something positive.

The reason for this is pretty simple: obvious disease, defect and deformity is much easier to tease out of the data pile than a reduction in an already rare pathology. One event is akin to a statistical loud noise; the other is simply a slightly longer continuation of the silence all around.

Of course no dog is born with a 100 percent guarantee of good health.

The health of dogs, like the health of all animals, is a roll of the dice.

Which is not to say that all dogs get the same set of dice.

To carry forward with the dice analogy, heavily outcrossed working dogs may be playing with a regular six-sided dice in which the chance of coming up with a pair of "snake eyes" (two ones) for a particular genetic defect is 1 in 36, or less than 2.8 percent.

A heavily inbred Kennel Club dog, however, may be playing with a six-sided dice that has the number ONE printed on three sides and the number TWO printed on the other three sides.

For that dog, the chance of coming up "snakes eyes" due to a "doubling down of genes" is one in four, or 25 percent.

In fact, many breeds have much higher rates of pathology than 25 percent.

Look at cancer for example. As I note in Making and Breaking Dogs in the Show Ring, more than 54% of Flat-coated Retrievers die of cancer, as well as more than 45 percent of Scotties, and 45% of Bernese Mountain dogs. Airedales have a cancer rate of 39 percent, Irish Wolfhounds 33 percent, English Setters 33 percent, Gordon Setters 29 percent, Irish Setters 27 percent, and Dobermans 26 percent.

All of these breeds have other problems too, of course.

There is a roll of the dice for every major body system: skeletal, circulatory, endocrine, and neurological, for example. A dog with a high incidence of cancer is not immune to other problems such as hip dysplasia, cruciate ligament injuries, heart problems, or epilepsy.

Today, scores and scores of Kennel Club breeds have serious health problems in which the probability of single-system defect is well over 25 percent.

Sometime this is is due to positive selection for pathology, as it is with dogs that have over-large heads which cause whelping issues, or dogs that have too flat a face (causing breathing and palate issues), or dogs that have achondroplasia (dwarfism) which is linked to both skeletal and heart issues.

Other times, however, it is simply a function of a small initial gene pool that happened to contain a regressive gene for one type of defect or another.

So long as the gene pool was large and otherwise diverse, the chance of that gene coming up in two rolls of the dice (one dice from the sire and one from the dam) was pretty low.

With a small population at the start, however, and progressive tightening of the pool through dominant sire selection and intentional inbreeding of the dogs to "improve" visible features such as coat color, coat length, and head size, defective genes are now much more likely to find each other.

The result is that defect and disease have reared up at startling rates in a huge number of Kennel Club breeds.

If you are looking to get a dog as a pet, do not swallow the blarney of a Kennel Club dog dealer who suggests that though his breed has a higher-than-average incidence of cancer or heart disease or cataracts, "you at least know what you are getting" in terms of problems.

In fact, all that Kennel Club dog dealer can REALLY promise you with his problem-riddled breed is that you are almost certainly buying into a higher-than-average chance of getting a dog with a serious, painful and expensive health care condition.

When buying dogs, caveat emptor is the watch word.

Do your research.

If a dog dealer tells you his "line" of dogs is free of all defect, assume you are being lied to, because you probably are.

When you read words like "cancer," "cataracts," epilepsy, heart defect, hip dysplasia, deafness, and skin disease, do not bounce too quickly to the next paragraph.

What is being promised here is that a lot of money will be hoovered out of your wallet, and a lot of time will be spent in veterinary offices.

Yes, a bad roll of the dice may occur with any dog, but remember that not all dogs are playing with the same set of dice. With many Kennel Club dogs, the dice are loaded for defect, deformity and disease.

• Other Links That May Be of of Interest
  ** Genetic Dog Diseases by Breed
  ** Individual Breed Health Survey Results (UK Kennel Club)
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