By Ermine Moreau-Sipiere


Today there is increasing public awareness of the significance of genetic diversity. Greater genetic diversity is considered advantageous in wild animals and plants, in order, for example, to decrease their sensitivity to environmental change. Genetic diversity is also considered advantageous in the total pool of domesticated animals and plants in order to provide source material for improved varieties.


Each individual variety of domesticated plant or animal does not, however, have great genetic diversity. The varieties have been produced by tailoring their genetic makeup to produce a single variety with specific, desired characteristics. The traditional tools to produce individual varieties are crossing and/or breeding in plants and animals.


This form of genetic manipulation has been practiced for thousands of years. The total gene pool (genetic diversity) for dogs is large. This is apparent when one considers all of the various breeds. Each individual breed has been produced, however, by selective breeding which restricts the breed’s gene pool to those genetic elements which produce only that breed. We do not want genes for long snaut in American bulldogs nor do we want genes for short legs in a Greyhound. We also do not want genes producing or allowing disease in a breed. The breeding methods used to produce and maintain a breed are the same as those which have been traditionally used to produce and maintain other domestic animals.


A dog’s phenotype is what we ‘see’ (including structure, function, and behavior), and its genotype is the genetic information the dog carries in its cells and will transmit to offspring. Perhaps, someday, genetic testing will be complete enough to determine genotypes for breeding purposes, but, until then, phenotype will remain our main method of judging dog’s genetic input. To achieve desired genetic results, all successful breeders, today and in the past, use and have used the systems of linebreeding and inbreeding. The results can be both good and bad. A breeder carrying out a serious program is trying, over generations, to keep desired qualities and characteristics of a breed and ameliorate or eliminate undesirable traits.


LINEBREEDING is ‘mating bulldogs who are closely related to the same ancestor but are little if at all, related to each other through any other ancestors’ (L.C. Brackett).


INBREEDING is a much closer cross between the ‘mating pair’ of bulldogs than is linebreeding: son to mother, father to daughter, brother to sister, half-brother to half-sister, brother to sister, and so on.


Some breeders would consider it inbreeding, others linebreeding, when crossing a dog to one of its half-brothers or half-sisters – offspring of one of the parents. Technically, there is a continuum from inbreeding to linebreeding just as there is a continuum in degree of relationship between dogs. As a result, it is sometimes very difficult to give the perfect definition. The definitions given above are the basis of the following discussion.


The purpose of both linebreeding and inbreeding is to bring improvement more rapidly and narrow the pedigree to a few closely related lines of descent. ‘This purifies the pedigree rapidly and enables a breeder to control, to some degrees, all characteristics’ (L.C. Brackett). Both linebreeding and inbreeding reduce genetic variability, often with the aim of eliminating genes for undesirable recessive characteristics.


It is easier to predict the results of breeding by linebreeding than to expect results from a breeding program that has no genetic basis. If the selection of the ancestors has been good, very few or no surprises should be expected.


Judicious linebreedings have long yielded, in all dog breeds and other domestic animals, important and real improvements. The quickest and most certain way to produce superior American bulldogs is by careful linebreeding, especially with a breed,which has little or no genetic disease.


However, there is a great danger in this system of breeding if the breeder considers only the pedigrees, without considering the physical, functional, and behavioural characteristics of the American bulldogs being bred and of their ancestors. Inevitably, the results are offspring with notable faults. A pedigree is a guarantee only of bloodlines and not of the qualities within those bloodlines. Unfortunately many beginners will consider only pedigrees, especially if they contain winners. They will breed without considering also the respective faults and qualities of the American bulldogs they want to mate. Consanguinity will concentrate not only the desirable qualities, but also the faults. Fortunately, truly serious breeders will study very carefully the properties the pedigrees represent. That is, they will study the family of the American bulldogs they want to mate (the qualities, the faults, the temperament, also the results in show, weight pulling, etc.) before linebreeding, to fix a type in their breeding program. That type will be the closest possible to the American bulldog breed standard, with robust health and desirable temperament.


Line breeding provides for early recognition of undesirable characteristics. A fault which is not apparent in the dogs in the pedigree can come out in a first or second generation because of the enhanced probability of the occurrence of two recessive genes for the same trait. Without the consanguinity of line breeding, the fault will probably appear much later and so, will take much more time to be eliminated. We are fortunate that dogs are born in litters of non-identical ‘twins’ so that probability of the fault appearing in one, but not all, puppies is enhanced.


Inbreeding is linebreeding at its extremes. The advantages and disadvantages of linebreeding reach their highest degree with inbreeding. This system of breeding aims to maximize the probability that all the qualities of the sire, in an example where the sire breeds his daughter, are retained in the offspring. If inbreeding is practiced, it is absolutely essential to study perfectly the ancestors of the sire in order to know their qualities and faults. Those faults must not appear in the daughter or in her pedigree because of the enhanced probability that the father-daughter offspring will inherit the undesirable genes of the sire. It is imperative to choose a sire who has qualities absolutely opposite to the daughter’s faults, and the daughter should have none of the faults of her sire who, in this example, is the sire of her puppies.


Not only the conformation, but also the temperament of the two dogs being mated by linebreeding or inbreeding must be taken into very serious consideration with the objective of securing and preserving only the desirable qualities.


When superior American bulldogs are used, inbreeding is the most powerful way to perpetuate their qualities and to influence the future of a breeding program. ‘Inbreeding is not so much a matter of originating excellence as of holding and making the greatest use of it when it appears’ (L.C Brackett). Inbreeding can be a disaster if practiced by an American bulldog breeder beginning with the wrong stock, or who doesn’t know the breed perfectly, or doesn’t know what is a very good individual. In this case, anyway, he or she should not be a breeder.


Good breeders linebreed or inbreed only superior individuals. A properly linebred or inbred dog is much more capable of reproducing its type than a dog which has outcross breeding.


‘It is known universally that any characteristics can be bred up or down, strengthened or weakened by inbreeding.’ Severe selection is the key to successful linebreeding or inbreeding; the good trait in one parent should be stronger than the opposite undesirable trait in the other parent.


When a breeder regularly produces litters with puppies with too much variance in type, he needs to consider linebreeding. He has the possibility of seeing the traits (dominant and recessive) in his dog. It is a risk, of course, but it is the only way for him to progress and try to produce homogeneous litters.


Linebreeding and inbreeding are not ways to bring new characteristics, but are proven ways to consolidate the best traits.


OUTCROSSING is a non blood-related connection, that is, the sire and dam are not related. After some generations of linebreeding and inbreeding, it is time to outcross. This also represents a danger for a breeder without experience.


L.C. Brackett writes, ‘after an outcross has been made, a breeder should then breed right back into the original strain. This is the only safe procedure after the purpose of the outcross has been achieved’. He explains, ‘a strain is a variety within a variety of animals’, obtained after successful linebreedings and inbreedings in a long and serious breeding program.


It is almost impossible to explain when it is time to outcross. After too many generations of linebreeding, there is a risk of producing smaller puppies and also puppies with a non-desirable temperament (too timid or too strong). Not all breeders agree that these risks occur, but many have experienced problems which they attribute to linebreeding.


When a breeder outcrosses, he can lose the type he has long worked to produce. He needs to introduce new genetic material only if the dog used can bring something necessary into his program and if he has linebred and/or inbred already several times. The breeder needs to know the ancestors of this ‘external’ dog perfectly, and what those ancestors can add to the line he has produced. In many cases, the level of danger inherent in inbreeding, linebreeding, and outcrossing can be equal when these breeding methods are practiced by a careless or inexperienced breeder.


The breeder must go back, after an outcross, into his established line, to perpetuate the ‘good’ brought into that line by the outcross. Of course it is also time to use an outcross when a breeder has not produced what he has wished or when he can have access to a superior dog or a very rare and proven pedigree which is not yet in his program. This system can bring qualities he needs, or correct a fault he has not been able to eliminate. Some people say that outcrossing can bring vigor, but linebreeding, when very carefully planned, should have the same result because vigor is a desirable trait which a breeder should linebreed for. The outcross can also bring undesirable traits. The breeder will have to hold the desirable qualities he has obtained with the outcross by returning to linebreeding with the progeny and should do the same to eliminate the bad traits brought by the outcross.


The general public believes that inbreeding produces bad temperament, lack of vigor, and poor fertility, and forgets that the same problems can arise with all other systems of breeding. It is the breeder’s responsibility, in any breeding program, to select for desirable characteristics and strenuously guard against undesirable ones. Of course, consanguinity is full of dangers, but it is a great tool when used by a careful breeder who knows the qualities and the faults of his dogs and their ancestors. He must be able to recognize sound conformation and temperament and needs to be knowledgeable in the area of genetics.


New breeders should not hesitate to ask the advice of very experienced and seriousbreeders.