Posted tagged ‘dogs’

How much do you really know about genetics and genetic health?

October 13, 2008

 

As an experienced dog breeder, dog judge and teacher, I am going to try and explain the significance and importance of genetic health because it is clear that many people, including those who made the television programme, Pedigree Dogs Exposed, do not have a clear idea of how genetics affects the development of species in general and pedigree dogs in particular. I am afraid it might be boring – but it is important. You can find a video of this talk on my web log at http://uk.youtube.com/user/davidcavill

We all live with genetic defects. I am short sighted and suffer from a number of allergies. My mother is short sighted and suffers from number of allergies too. I have a friend who is epileptic – as was her mother. Another is diabetic and I have just heard that someone close to me has developed breast cancer. All these conditions have a high ‘hereditability’: that is, their genetic component is significant. If you are the direct descendent of someone who has any of these conditions you will not necessarily get them yourself – but the likelihood of them occurring is much higher that it would otherwise have been. Scientists have identified around 3,000 genetic defects in humans and about 300 hundred in dogs.

This is not the place for long explanations but there are some words which have been used wrongly in the recent furore surrounding the Pedigree Dogs Exposed programme and in the programme itself. They have emotional overtones that add to misunderstanding and bias so it might be helpful to go through some definitions.

Firstly a ‘genetic condition’ refers to a physical or mental disorder caused by an absent or defective gene or by a chromosomal aberration. The make up of the genetic material of the sperm and egg is such that the DNA of the resulting embryo is damaged and the development of some characteristics is distorted. Most damaged embryos are detected and are aborted but many are not, so the embryo survives and is born. At this stage the condition may mean the baby will not survive. In some cases the child is severely disabled but in most cases and more commonly the child become an adult and learns to live with the condition, often with the help of medication.

This is not the same as a ‘congenital condition’. This is where the original embryo was fine but suffers damage between fertilisation and birth. The mother smoking, drinking or taking recreational or prescription drugs may cause congenital conditions. The best-known example is the conditions directly caused by the drug thalidomide being prescribed to women who were pregnant.

A mutation is quite different. In genetics, a mutation is a permanent, transmissible change in genetic material as a result of a miscopying of a section of DNA. This can be caused by environmental factors (radiation, for instance) or by the age of the mother or the father because eggs and sperm deteriorate over the years. It is mutation which has produced us! It is the whole basis of evolution and without it we would not exist. But the important point is that is it entirely random. Most mutations have little effect but occasionally one turns up which improves the organism’s chances of survival. To describe any living creature with genetic disability as a ‘mutant’ shows deplorable ignorance from a scientist or anyone who has even a basic knowledge of genetics.

As humans have developed companion animals to be more and more useful there has been a conscious desire to ‘fix’ certain characteristics. At the simplest level it was breeding dogs which were faster to help with hunting and bringing down animals which humans could not catch on their own and later, as nomads become farmers, cows were bred to give more milk for longer periods, sheep for more coat to provide fleeces which would give more wool, chickens to lay more eggs and all them as well as pigs, goats and geese to give more meat. This process, called ‘selective breeding’ is common throughout agriculture

However, ‘fixing’ one characteristic which was desirable could also fix others which were less so. Random liaisons between animals tend to keep their DNA healthy (this is called ‘hybrid vigour’) although, as we have seen in humans, it cannot do so altogether. It is for this reason that most societies forbid marriage between those directly related to each other although many societies are comfortable with a cousin marrying a cousin and if both are fit and healthy there is not normally a problem. And there are plenty of examples where cousin-to-cousin marriages have been contracted down several generations without any difficulties. The reason is that what is called the inbreeding coefficient (the measure of how close two people are genetically related to each another) of a cousin to cousin relationship is just 6.25% and for most couples in this position there is little likelihood of serious genetic defects arising although, of course, there is always a risk. However, most relationships have an inbreeding coefficient of much less that 6.25% – but because of the complexity of human DNA many children are still born with genetic defects. Most are minor although there is always the chance of something very serious – but this can happen between people who are not at all related. Genetic defects are in our genes and will sometimes occur. This is very simplistic, of course and there is an array of mechanisms which result in specific conditions such as haemophilia (which is caused by a sex-linked recessive gene) and others where the recessive is expressed on both sides of the DNA.

Most pedigree dogs are ‘line-bred’; that is they are mated to members of the same family although seldom very closely. In fact, the average breeding co-efficient on the Kennel Club registry is between 5 and 10%. Inbreeding where fathers are mated to daughters or vice versa or mothers are mated to sons or vice versa) is not common: less than 1% of puppies on the KC register are the result of inbreeding which is defined as being anything mating with a breeding coefficient of over 25%. A common rule of thumb for dog breeders is ‘line-breed two generations and then outcross’. Basically this means that in each two-generation ‘layer’ of a pedigree you will find the sire and the dam of the puppies more than once but in every third ‘layer’ you would find a dog which was not repeated anywhere.

In dog breeding, responsible breeders will try to select dogs and bitches which are good examples of their breed and, these days, most will ensure that their stock is not carrying serious defects. This is not true of everyone, of course – and I am afraid that those who breed large numbers of puppies without the expertise and care the dogs deserve, often have little regard for their health and welfare.

However, what was not made clear in Pedigree Dogs Exposed was that there are two quite separate issues here. They are ‘genetic conditions’ and ‘conformation’. Although they are connected it helps if we look at them separately.

As we have seen with other companion animals, is relatively easy to change the conformation and performance of an animal by selective breeding. Frisian cows are bred primarily to give milk – their flesh is not very suitable for meat and most meat from Fresian cows ends up in meat derivative products such as pies, sausages and dog food because it would look very unappetising on a butchers counter. At the other end of the scale, Aberdeen Angus give exceptional meat but their cows give little milk.

When countrymen wanted dogs which would go to ground and flush out vermin they were able to produce dogs with the right conformation by selective breeding very quickly. In fact, it has been shown in experiments at the turn of the last century that, given a group of mongrels, a breeder can produce a creditable example of any breed within five generations. You like the idea of a hairy dog with a flat face? Just collect some small, hairy mongrels and mate them. Select those puppies with the shortest muzzles and mate them. Continue the process and you very soon have a Pekingese! The Dobermann and the Leonberger and our British Gundog and Terrier breeds were all ‘created’ in just this way. It is simple and it works. However, it is possible to take a specific characteristic too far as has happened with some breeds and this will inevitable lead to problems of conformation. This is not the same as deleterious, damaging genetic conditions. Bear with me.

As you change the conformation of the dog by selectively breeding them for shorter legs, longer bodies, more skin or deeper, wider and rounder chests, the rest of the dog’s anatomy is stretched or compressed to fit. Up to a point this does not matter. As I explained in my previous talk, so long as the dog can eat, breath, walk and run, mate and whelp normally then its conformation and head shape is unimportant. But once its conformation affects those natural behaviours then however attractive the breeders and potential owners find the look of the breed, their conformation should be modified. It is easy – you just reverse the process. You do not have to start again. Four or five generation is all it takes.

However, in getting a desired conformation there is a tendency to use the same small group of dogs and if they have a deleterious genetic condition, a disease, then this will become endemic within that breed. This is what has happened with dogs which should be perfectly sound from the point of view of their conformation. It is usually because breeders have relied on too narrow a gene pool – and in some of the smaller breeds this gene pool is very small. These conditions are more difficult to breed but it can be done by introducing dogs from outside the breed into the breeding programme.

This can and has been done (with Kennel Club approval, I must add) and I am sure that in the next few years it will be done much more often. But I must emphasise that although some of these genetic diseases conditions are serious and, of course, very distressing for the owner, the majority, like short-sightedness in humans, are a minor inconvenience which can be treated or managed. So the incidence of a genetic condition in a breed does not mean all the dogs are ill or damaged. Some will be, I am afraid but for many or most their dysplasia or patella luxation is nothing more than a minor inconvenience. Few dogs die of genetic disease. If is serious they do not survive beyond the womb in any case

And it is also important to note that for many or even most breeds, deleterious genetic conditions have a very low incidence. They are there, just as they are in humans and in other animals but, in general, they are as fit and healthy as any mongrel you might take home from a dog rescue centre.

Go to a dog show and see for yourself

Pedigree dogs exposed programme Exposed

October 12, 2008

This talk appears on You Tube at http://uk.youtube.com/user/davidcavill

My name is David Cavill. I have bred pedigree dogs for over thirty years and I judge many breeds both in Britain and all over the world. I have also worked extensively with rescue dogs too.

In my lectures on breeding and judging dogs there is a major section at the beginning of my talk about how dogs came to be as they are and it might help those who have assumed that everything in the recent television programme Pedigree Dogs Exposed was ‘gospel’ that there is another side to the claims which it made: another side which shows that many of the statements made were seriously distorted and designed just to grab headlines. ‘Headlines’, of course create a bandwagon and many individuals and organisation have jumped on board. In this the producers were extraordinarily successful.

Firstly a few facts: a groomer friend of mind sees dozens of Cavalier Charles Spaniels every month and has never seen a dog with the symptoms described in Pedigree Dogs Exposed – which is not surprising as the incidence is estimated to be about 2%. The programme stated that the incidence was ‘up to 30%’. This is not, in itself, untrue but implies a proportion which is it approximately fifteen times the correct figure!

Several people have called for the Boxer shown in the programme to be put to sleep and even for the owners to be prosecuted for cruelty in that they are keeping an epileptic dog alive. The truth is that the dog is under successful medication and fits ‘about once a month’.

The statement by the RSPCA Vet has been criticised by senior members of his own profession. It is inaccurate and untrue and the RSPCA has since had to withdraw support for it.

The incident of dogs with an inbreeding coefficient of 50% (that is mother to son or vice versa or father to daughter or vice versa) is less than one percent. The average inbreeding coefficient of pedigree dogs on the Kennel Club registry is less than 5%. To put this in perspective, if someone marries their cousin (a very common occurrence in many human societies) the inbreeding coefficient is just 6.25%

There are many other examples of the way in which statements have been taken out of context to ‘prove’ the allegations made in the programme. Beverly Cuddy is a past master of the technique. She is a friend of mine, incidentally but with a long history of prejudice against pedigree dogs for personal and political reasons despite the fact that she is, herself a championship show judge of Bearded Collies. She says in the programme ‘ pedigree dogs are falling apart’. I suspect that this quote was taken out of context for it is demonstrably not true as anyone who goes to a dog show can see for themselves and I delighted to say that she, like the RSPCA and Dogs Trust, has found it necessary to publicly modify their stance.

This is not to say that there are no serious problems within the world of pedigree dog breeding: there are and they must be addresses. But the truth is very different to the message which Pedigree Dogs Exposed tried to deliver which was that all dogs were damaged or crippled. Firstly, though let us see if we can understand the way in which ‘the normal’ translates to ‘the exaggerated’ and, finally to the ‘deformed’ in the breeding of animals.

In my lectures I begin with a picture of a mongrel, which I describe as an unexaggerated dog. It is about 14 inches high at the shoulder, a little longer than it is high, neither heavy or thin and with a medium length single coat similar to that which might find on a working Irish Setter. When I was one of the senior managers at Battersea this was typical of hundreds of dogs we were asked to re-home (times have changed but that is anther and longer story). Whether it is typical of the dogs that hung around human encampments in the days when most of us were nomadic travellers I do not know. I suspect that semi wild dogs then were leaner and ‘racier’ but what I am sure of is that if you left a thousand of our 21st Century pedigree dog and bitches together in and enormous enclosed game park and let them loose, a large proportion of dogs similar to the one I have described would be the result after four or five generations of breeding,

Why should this be? Firstly some of the breeds would not survive into the second generation because they would not be fast enough to catch game or get to ‘kills’ in time so would not be able to hunt and feed themselves while others would not be able to mate or whelp naturally so there would be no puppies from these breeds. Of the rest some would be more adept at foraging for food than others and, if the space were varied enough, it would not be long before the dogs most adapted to specific environments would migrate to those areas where they would have the best chance of survival. So you would have some variety in size, weight and conformation (and temperament, too, of course) but a sizeable number would be like my Battersea mongrel: perfectly adapted for the widest type of terrain. Of the more specialist types you would see some leaner, with longer legs and deeper chests, others, probably fewer, would be thicker set and be heavy enough to bring down slower but bigger animals: our mongrel would do well from the scraps left by those other groups as well as being fast enough to catch small (and often elderly or ill) game.

Now bring in a human dimension, To begin with ‘man’ refines and improves what he has, but essentially, dogs that can be helpful survive and those that cannot are rejected and either are killed or become household pets and children’s’ playthings. Remember the same process was also going on with other domestic animals – cows were being bred that would give more milk for longer, sheep for thicker coats to give more wool, pigs for more piglets in a litter which would grow to maturity with more lean meat and less fat – the process was not confined to dogs.

As far as dogs are concerned a few types were developed for more specialist uses over the millennia. Dogs for herding, dogs for war and dogs for hunting (for fun rather than for food) but eventually people began to use the extraordinarily flexible chromosomes of the canine genome to produce animals radically different to ‘the norm’ in just the same way as breeders of cats, horses, budgerigars, pigeons  and roses for that matter have done for centuries.

Dogs became longer, shorter, taller, thicker set, shorter muzzled and lower to ground in terms of conformation, and hairier, smoother or slacker skinned, wrinkled, double coated, fancy tailed, fancy eared and multi-coloured in terms of their individual characteristics.

I emphasise that I have no problem with any of this but there is a point when the changes introduced militate against the best interests of the dog in terms of its health and welfare. My talk asks the deceptively simple question ‘Where is that point?

I hope I have shown that it is not unreasonable to breed specialist dogs for our own pleasure and/or for the pet owning public so long as they are well cared for and remain fit and healthy.

A breeder may feel, aesthetically, that they would prefer their dog’s ears to be a little more upright, longer or better set; they might want the eyes darker or the coat longer; they might want more or less of a stop or a broader or narrower width of skull – all of these characteristics are ones which are peripheral and acceptable. Coats can be washed and groomed easily so they are not an issue whatever you think of Poodle cuts of the length of the coat on a Yorkshire Terrier, but under normal circumstances, skulls cannot be enlarged, bones cannot be lengthened or shortened, livers and lungs, hearts and throats and eyes and noses cannot be replaced so these are the physical characteristics where ‘the question’ becomes important.

I offer you this definition: as soon as an animal is finds it difficult to eat or chew ‘normal’ food, has difficulty in breathing under all normal circumstance, finds it difficult to keep up with its owner at a brisk walk, cannot under normal circumstances mate or whelp naturally or they die well below the average age one expects a dog to die, then it is important that breeders take a long, hard look at what they are doing.

This has already happened in many breeds and the Kennel Club has put pressure on many others to take action. The Chow Chow is an excellent example: from being a dog with real problems with its conformation, eyes and muzzle it is now, in the UK at least, a pleasure to judge. And in terms of temperament, the Kennel Club brought in a regulation almost fifteen years ago that if any dog bit within a dog show the dog would be banned permanently from showing and all its progeny banned permanently too. The effect was immediate and the incidence of dogs biting people or other dogs at a show is now very rare.

Pedigree Dogs Exposed has forced the hand of the Kennel Club and I know the Chairman and others, including Kennel Club staff, are actually pleased to be given this lever to force through further improvements.

But it must be made clear that the proportion of dogs affected in these ways is relatively small. The vast majority of pedigree dogs live long healthy lives and, in fact, there is no statistical difference in the life span of pedigree dogs and mongrels. If you go to any veterinary surgery the number of pedigree dogs and mongrels you will see are equally balance – about 50/50 – the same as the proportions as in the population as a whole!

Go to a dog show: see for yourself.