Introduction

After the BBC programme “Pedigree Dogs Exposed” the canine world will never be the same again. The media and governments will continuously put demands on pedigree dog breeders and Clubs.
The best thing that breeders can do is to take their own fate in hands and come out with positive proposals which will improve the health of the dogs and take care of the future of the breeding population.
The “Cavaliers for Life” project is a good example of such an initiative started by breeders from different countries.

Hereditary diseases

Paul Mandigers and Laura Roest

The Cavalier King Charles Spaniel has been the subject of over 100 scientific studies performed within the last five decades. Thanks to the scientists investigating the diseases we know more about the CKCS and its (hereditary) diseases than several other breeds. Sadly enough this made the CKCS an easy target for the media which had a devastating influence on the way people look at the CKCS. But it also placed the CKCS and its breeders in a unique position to deal with the several issues supported by officials, politicians, veterinarians and other breeders.

Two diseases with clear clinical consequences and a high prevalence exist within this breed. Both diseases occur within several other breeds but exact knowledge on prevalence in these other breeds is lacking.

MMVD

The first disease that has been studied is myxomatous mitral valve degeneration (MMVD). It is also known as mitral (valve) regurgitation or mitral valve disease. The mitral valves are the functional closure between left atrium and left ventricle. Oxygenised blood coming from the lungs flows towards the left atrium. From the left atrium it flows towards the left ventricle. As the left ventricle contracts the blood is ejected into the aorta towards the body. If MMVD arises the mitral valves cannot fully close with as a consequence regurgitation of blood back into the left atrium. In early cases it will have no clinical consequence at all. But in some cases it can in the course of years introduce severe left atrial dilatation and failure of the left ventricle. At the beginning of the disease the dogs will show no clinical signs and it can only be detected by cardiac auscultation revealing a soft murmur. Early clinical signs are a mild increase in heart frequency, coughing (it can be both soft and loud) and in time it may progress to reduced exercise tolerance, weight loss and pulmonary effusion. MMVD is a disease affecting both man and dog. It affects all breeds but the problem with MMVD in the CKCS is its presentation at young age (so called juvenile MMVD). Based on earlier research the prevalence of juvenile MMVD (at the age of 6) is 50%, and MMVD at older ages approximately > 90%.

CM/SM

The second disease is CM/SM. CM stand for Chiari-like malformation and SM for syringomyelia. Chiari-like malformation is a disorder in which the cerebellum (the small brains) herniates through the foramen magnum (great hole) pushing on the latter part of the brainstem.

Most likely this causes in the CKCS an abnormal flow around the spinal cord causing a dilatation of the central canal and syrinxes (fluid filled cavities) in the spinal cord (see figure). Many CKCS may show no signs at all. However, early cases may show signs such as phantom scratching towards the neck, sudden outbursts of pain, head rubbing and facial pain. More severely affected CKCS can even show neurological deficits such as ataxia (uncoordinated locomotion) and continual pain attacks. Based on earlier research the frequency of CM within the CKCS is approximately 95%, of SM more than 50%. The prevalence of clinical cases is around 8 to 10%. The frequencies of both diseases (MMVD and CM/SM) may differ in the various countries as the populations can be different.

Working plan for the CKCS breeders in the Netherlands

CKCS breeders are faced with two well-spread diseases.
In order to deal with them the Dutch Kennel Club, The Cavalier Club of the Netherlands, Breeders and veterinarians and scientists of the Universities of Utrecht (The Netherlands) agreed to breed according to the following guidelines (as of November 2011) to obtain as much data for the breeding programme “Cavaliers for Life”:

CM/SM

• All possible breeding dogs will be scanned before they are allowed mating. Scan results are categorised using three age groups.
• All the scan are made at certified MRI centres all using the same method.
• All MRI scans will be judged by a European board of certified radiologists and neurologists.

MMVD

• The first cardiac examination of a possible breeding dog consists of a proper cardiac examination (this includes, among others, auscultation) and an ultrasound of the heart before the dog is mated.
• Each year a cardiac examination. No murmur suggestive for MMVD is allowed before the age of five.
• Follow up will be performed until they reach at least the age of ten years.
• All ultrasounds will be made using the same protocol by certified centres. All auscultations will be performed by board certified specialists in cardiology or internal medicine.

DNA

Of all CKCS selected for breeding at the time of the MRI scan a sample for the isolation of DNA will be taken and stored.

Breeding programme “Cavaliers for Life”

Arnold Jacques, Pauline Jordens

We all know that the measurements and performance of an individual dog are insufficient to predict accurately the genetic predisposition of a dog. A breeding strategy based only on results of individual dogs is not efficient and can be dangerous for the future of a breed.

Two years ago we started a private initiative with the purpose of developing a breeding advice programme based on Estimated Breeding Values (EBV’s) for the Cavalier population.

We have developed a computer program especially for this purpose. The first two countries to join the programme were The Netherlands and Belgium. The pedigrees of all the Cavaliers born since 1995 in these two countries were entered in the database.

The University of Leuven (Belgium) under the guidance of Dr Steven Janssens has made a complete report on the genetic diversity and the inbreeding coefficient of the Cavaliers born since the last 15 years in these two countries.

The report concludes with the following statement: Any breeding strategy will be decided by not only the occurrence of one or more genetic disorders, but also by the size of the genetic diversity of the breed. From a scientific point of view, the best solution for the Cavaliers population is the use of Estimated Breeding Values (EBV) in combination with inbreeding limitation ("Optimal genetic contributions").

What are EBV’s and how do we calculate them?

A breeding value is a mathematical method in which the genetic predisposition of an animal for a particular trait can be estimated. It estimates how well the animal as a parent for the next generation will be. In other words: it estimates the value of the animal for breeding: this is called the ESTIMATING BREEDING VALUE.

First of all we gather as much information as possible about the dogs (pedigrees, health screenings, assessments, etc.). This information is entered into a specially designed computer program in a standardised manner.

The data is processed into breeding values based on the animal model. The calculations are done by the BLUP system (BLUP = Best Linear Unbiased Prediction).

How does this work in practice?

A breeding value is a number per dog and per trait. For each trait the figure 100 is always the average of the breed. The higher the number, the better the dog passes the trait to his descendants, the lower the figure the less the dog passes the trait to his descendants.
When we deal with negative traits (hereditary disease) a dog with a lower figure passes on the disease less than a dog with a higher figure.

It is recommended to do better in each generation, we must therefore ensure that the EBV of a litter is lower or equal to 100. The EBV of a litter is the average of the EBV of both parents.

EBV’s in the time

EBV’s are based on the animal model, they are not fix in the time. EBV’s of a dog can even change without entering new data of the dog, due to new data from related dogs.

Breeding advice (mating list)

When introducing EBV’s in a breed, there is always the risk that breeders will only use the dogs with the best EBV’s (= Champion culture). This will lead to exclusion of valuable dogs and finally result in narrowing the breeding pool with the famous bottleneck as a result.

© B. Kutsch

Therefore, it is recommended in the beginning not to publish the individual EBV’s of each dog. Instead the computer will calculate for each bitch an individual list with all the appropriate males (based on the EBV’s of the combinations).
The breeder will receive this list with all the appropriate males (based on EBV’s) in alphabetic order. By choosing either of these dogs, the breeder will produce a litter with EBV’s better than the average of the breed. In this way, the population will improve by each generation.

In the future, when a breeder chooses a combination according to the breeding advice, a note should be printed on the pedigree of the puppies, certifying that this puppy is originated from a scientific responsible combination.

“Cavaliers for Life” project

The project can be considered as a pilot project. It is a private initiative set up by breeders from several countries working close together with Universities, genetic people, vets, judges etc.

Many volunteers are working very hard together to make this project a success. The funds are managed by a non-profit organisation.

Many breeders have contributed financially. We are very grateful to the Dutch Kennel Club (Raad van Beheer) and the Scientific commission of the Belgian Kennel Club (St. Hubertus) for helping us to fund this pilot project.

At present we have over 24,000 pedigrees of Cavaliers in our database. We have started to collect data from MVD screenings, CM/SM scans, eye reports, DNA tests (Episodic falling syndrome and Dry Eye/Curly coat).

More information can be found at www.cavalierpopulation.com