The case for intervarietal matings between Groenendael and Tervueren dogs and how this might operate.
It is generally assumed that present day dog breeds are based on a relatively small number of founder dogs and that the early stages of breed development involved high levels of inbreeding and very intense genetic selection in order to quickly fix the desired breed type and characteristics. The consequence is that essentially the only genetic diversity in the breed stems from that provided by those initial founder dogs and retained in the small number of progeny that were selected to expand the breed. Early in this process a unique breed register will have been adopted, imposing a breeding restriction to registration such that litters were only registered in the breed if both parents were registered members of the breed, which, of course, exists to the present day.
As the breed numbers expanded over the years breeders have adopted particular breeding strategies in their attempts to improve the breed and there is no doubt that for the most part present day dog breeds are the better for these efforts. For most of today’s breeds the efforts of the breeders over the last few centuries have led to generally improved conformation and health. For some breeds, these improvements have included past, sanctioned interbreeding programmes to effect positive change. However, these breeding strategies have had other consequences and have led to populations of purebred dogs with limited genetic variation.
About five years ago now the Kennel Club entered a collaboration with a group of scientists at Imperial College, London in an attempt to better understand breed genetic structure and the impact that breeding practices have had on it. This initial investigation focused on 10 different breeds, varying from those that were numerically small up to the Labrador, which represents the numerically strongest of today’s KC-recognised breeds, and involved analysing data from the Kennel Club’s electronic breed database. This analysis has been continued for other breeds via a new collaboration with Dr Sarah Blott and her colleagues at the Animal Health Trust, a collaboration which has been cemented by the creation of the Kennel Club Genetics Centre at the Animal Health Trust. This will enable continued investigation into breed genetic diversity and the outcome of this will allow breeders in the future to not only improve breeds and their health issues but also to do so in a way that will not have too serious an impact on genetic diversity. It will hopefully also allow experienced breeders to exercise the choice and judgement which they have been able to use in the past, but with an added scientific dimension to assist them.
One of the consequences of pure-breeding is that over time the average inbreeding coefficient of the population will rise. In all of the breeds studied there has been a constant increase in the breed’s average inbreeding coefficient throughout the period covered, amounting to between a 1 and 2% increase per generation, depending on the breed. The rate at which the inbreeding coefficient goes up depends on the effective size of the population. The smaller the effective population size the faster inbreeding accumulates. The effective population size has a rather complex definition in population genetics, but it might help to think of it as the number of individuals in a population who contribute offspring to the next generation.Of the 10 breeds initially studied in the Imperial College collaboration, the Labrador had the highest effective population size at just over 100; three others had effective population sizes between 65 and 75 and the remaining 6 breeds had effective population sizes less than 50. To put this into context, conservation biologists become concerned if the effective population size drops below 50.
It is known from other species that increased genetic risk comes with increases in average inbreeding coefficients of more than 1% per generation, often expressed as a loss of either reproductive or immunological viability. So, in future, managing these risks will become paramount for purebred dog breeds. Future breeding strategies will have to be devised to slow down these effects. There is a great deal of work still to be done in order to understand the best ways of managing risk, but there are some pointers even now. For example, we can reduce the reliance on popular sires and try to encourage more bitches to be bred from but in doing so we must of course take care not to create other problems for the breeds concerned. We can also encourage the mixing of populations of the same breed that have been geographically separate for some time through the importation of dogs or semen and the use of artificial insemination.
The breeds that are essentially based on allele differences of just one gene, rough versus smooth, smooth versus long versus wire haired and those based on a simple coat colour allele, are fortunate and offer another way of managing potential genetic risk due to reduced breed genetic diversity. These breeds are essentially varieties that have been kept artificially separate through the creation of a breed register and so intervarietal matings could contribute positively to managing future genetic risk by allowing the mixing of the two separate gene pools. Furthermore, the outcome of such matings, in phenotypic terms, is essentially predictable. Against this background the General Committee of the Kennel Club last year discussed the possibility intervarietal matings, as a matter of fundamental policy, and accepted a general proposal to consider encouraging intervarietal matings in the relevant breeds and the registration of any subsequent progeny on the breed register defined by their phenotype. It was decided that proposals, submitted ahead of a proposed mating by either a breed club/council or an individual, were to be evaluated on a case-by-case basis. The first such proposal was received in Belgian Shepherds and this was approved; the second a proposal to mate Miniature Smooth Haired and Miniature Wire Haired Dachshunds.
So, how might this approach work for Groenendael and Tervueren? Well, it is relatively easy to see how the general approach already approved by the General Committee could be used to the benefit of both breeds. The important principle is that any intervarietal matings should be approved ahead of time and that sufficient information is recorded to allow the matings and subsequent descendants to be tracked. With this in mind, each proposal for intervarietal matings between Tervueren and Groenendael should be considered on a case-by- case basis and resolved on its merits.
The starting point, of course, will be a mating between a Tervueren and a Groenendael, to produce what is called an F1 litter. The prediction is that all of these F1 puppies will be black, because the black colouration is dominant, and so the proposal would be that F1 puppies will be registered on the Groenendael register and their registrations be annotated with three asterisks. These puppies are black because they have inherited an allele of just one gene that determines coat colour, but generally, all of these puppies will have 50% ‘Groenendael DNA’ and 50% ‘Tervueren DNA’; the asterisk system, as I hope will become apparent later, reflects the relative proportions of this DNA and the single coat colour gene will determine the breed for registration purposes. Of course, it is possible that the Groenendael used for the initial intervarietal mating is a Groenendael that is carrying the recessive Tervueren coat colour allele. In this case, the F1 litter will be a mixture of puppies, some of which will be black and others will have the Tervueren colouration, roughly in equal proportions. If this was to happen, the black puppies will be registered on the Groenendael register and the Tervueren-coloured puppies on the Tervueren breed register, with all of the puppies being registered with three asterisks.
These F1 puppies can then be used to the benefit of both breeds by subsequent matings that will help the mixing of the two breed DNA pools. There are three general proposals that can be developed following this initial cross:
- Black F1 puppies, registered as Groenendael and annotated with three asterisks could be mated to dogs from the Groenendael breed register to produce an F2 litter. These puppies will be black and will be registered as Groenendael with two asterisks. Why has the asterisk number dropped? Well, the initial F1 dog had 50% Groenendael DNA and 50% Tervueren DNA. This will change in these F2 puppies which will now have 25% Tervueren DNA and 75% Groenendael DNA, so the asterisk drops to two to reflect this change. F2 puppies can than be mated to other Groenendael to produce a F3 litter which will be registered as Groenendael with one asterisk. So, by the F4 litter the descendents of the initial cross will be fully integrated onto the Groenendael register and Tervueren DNA from the initial cross will be incorporated into the Groenendael DNA pool.
- If there are F1 puppies with Tervueren colouration, these can be back crossed to dogs from the Tervueren breed register with progeny being registered as Tervueren with two asterisks in the F2 litter and one asterisk for the F3 puppies and no asterisks in the F4 and later litters.
- How might the Tervueren breed benefit from intervarietal matings if all of the F1 progeny are black and registered as Groenendael? A second general proposal would involve mating one of the black F1 puppies to a dog from the Tervueren breed register. This will provide a F2 litter that will be approximately 50% Tervueren-colour and 50% black. However, irrespective of their coat colour all of these F2 puppies will have 75% Tervueren DNA and 25% Groenendael DNA. The Tervueren F2 puppies will be registered on the Tervueren breed register with two asterisks. One of these can then be mated to another dog from the Tervueren register to produce a F3 litter of dogs that will all have Tervueren colouration, which will be registered on the Tervueren breed register with one asterisk, and so on.
- What about the black puppies in the F2 litter produced by crossing an F1 puppy with a Tervueren? These clearly have one black allele of the coat colour gene and because this is dominant these puppies are black, but they actually are made up of 75% Tervueren DNA and 25% Groenendael DNA. I would propose that these puppies are registered as Groenendael, but retain their three asterisk annotation. These could then be mated successively to other dogs from the Groenendael breed register and their progeny registered as Groenendael, because all of them will be black, with the loss of an asterisk at each new generation, until all of the asterisks have been lost.
Since some of these proposed intervarietal matings will re-introduce the recessive Tervueren coat colour allele into the Groenendael breed gene pool, it is imperative that cross registration continues in order to accommodate the consequences that might ensue.
Some concerns have been raised by members of the clubs that acceptance of intervarietal matings, as outlined above, might inevitably lead to the re-integration of the four existing breeds into a single breed by the Kennel Club, as happened in the past. The following statement from Mr Ronnie Irving, Chairman of the Kennel Club, should allay such concerns:
"I confirm that the Kennel Club wishes to encourage the use of intervarietal matings because of the benefit that they can have to breed population structures. I also confirm that in so doing, the KC has no intention of insisting that breeds which take advantage of such a facility be brought together as a single breed for the purposes of CC allocations, stud book and other classifications etc.”