Breeding Leonbergers
 

"A dog is an incredibly complex organism made up of millions of cells too small to see with the naked eye. Each cell (the basic structural and functional unit of life) cooperates with all the other cells to sustain the life of the organism. Attempting to produce a show-quality Leonberger out of this complexity involves a basic understanding of the principles of genetics. Though scientists are beginning to understand the complexities of genetics, much remains a mystery. Still, some basic principles apply to the breeding of all living organisms, including dogs.

 

A dog begins as a single cell (fertilized egg) that contains all the genetic information necessary for guiding that cell's growth and development into a puppy, as well as for the later maintenance of the dog throughout its life. During embryonic development, the original single cell divides into two; these two divide to form four cells; and the number of cells continues to grow with each cell division cycle until a puppy is produced. Besides cell division, the cells become structurally different from one another; the variety of cell types becomes capable of different functions. Genes (the basic units of inheritance) guide these processes of cell division and cell differentiation, eventually producing a puppy composed of millions of different kinds of cells. If something goes wrong during the complex processes of embryonic development a puppy may have a congenital structural defect (cleft lip/palate, for example). Congenital (present at birth) is not the same as genetic (which means inherited). A congenital birth defect (or disease) may have a genetic cause, or is linked to environmental factors, or it may even result from a random developmental "accident.”  Also, a dog may be born with genes that cause a certain disease, but the disease itself  (for example, certain types of cataracts), may not develop or become apparent until later in the dog's life.

 

Each of the millions of cells that comprise an organism will consist of cytoplasm (a watery soup of chemical substances with different kinds of small structures dispersed throughout it), and a nucleus (a membrane-enclosed region that contains the cell's genetic material). The nucleus is the cell's control center giving the cell its directions. Genetic material (long molecules of a chemical called DNA) is contained in microscopic structures called chromosomes. The chromosomes occur in matched pairs called homologous chromosomes (homo meaning alike, logos meaning structure). Except for the pair of homologous chromosomes that determine the individual's sex (which are of unequal sizes in a male), the two members of each pair are the same size and are made up of the same genetic subunits called genes. Envision each chromosome as a string of pearls that are strung together in a row, with each pearl different from all the others. Each pearl represents a gene.

 

Each species has its own characteristic number of chromosomes: a dog has 78 chromosomes (or 39 pairs of homologous chromosomes). By comparison, a horse has 64, a cat has 38, and a human being has 46. In each species of mammal, one pair of chromosomes (called the sex chromosome pair) determines the sex of the individual. The female has two sex chromosomes similar in size and carry the same kinds of genes-- these are called X chromosomes. The male has one X chromosome that is paired with a smaller sex chromosome made up of fewer and somewhat different genes--this smaller sex chromosome is called the Y chromosome. Some genes located on the X chromosome (sex-linked or X-linked genes) control traits that have nothing to do with sex. These traits are inherited differently in males than in females, since a male may have only a single copy of a sex-linked gene instead of two. The male determines the sex of the offspring, since a sperm carrying an X or a Y sex chromosome fertilizes the egg.

 

Each parent, through its egg or sperm, gives each of its offspring a half-set of 39 chromosomes (or one chromosome from each of the 39 homologous pairs). When a mother's egg containing 39 dissimilar (non-homologous) chromosomes becomes fertilized by a father's sperm containing another set of 39 non-homologous chromosomes, the mother's and father's half-sets of chromosomes pair up to reconstitute the double number of 78. These chromosomes carry the genes that will control all of the newly developing puppy's physical characteristics or traits (and to some extent, its behavior). Some genes work alone, while others work in association with different genes (sometimes on different chromosomes) in controlling the development and ultimately, how the new individual functions. Not all genes within a cell are functional at all times. Some may function in one type of cell and not another; some may become active at a later phase of a dog's life, but not at the beginning. The ways in which the inherited genes are translated into physical traits in the puppy and dog are complex. The development of a genetic linkage map of the dog genome will answer questions of inheritance in dogs. The comprehensive canine genetic map will identify genetic markers linked to inherited diseases, and use these linked markers to develop genetic screening tests. The tests will be used to eradicate diseases by selectively breeding from healthy dogs. Work on the canine genetic linkage map has been in progress as part of an international collaboration of 46 laboratories in 20 different countries. (Visit the NIH website to see the progress on mapping the canine genome.)

 

Except for the sex chromosomes, each chromosome consists of genes similar to those on the other member of that chromosome's homologous pair, and located at the same site on the chromosome. A pair of genes, one each on each of the two members of a chromosome pair, is called allelic genes (or alleles). Alleles are different forms of a gene that control a given trait, so the two alleles of a pair can be either identical to or different from one another. Each allele in a pair contributes to the development of whatever trait that gene controls, such as the long-coat trait or the coat color trait. If a puppy inherits a different gene allele from each parent, and two alleles for this gene or trait are not alike, it is called heterozygous. If a puppy receives identical alleles of a given gene or trait from each parent, and the two members of the allelic pair are the same, it is called homozygous.

 

A gene or the trait it “controls” may be called dominant, recessive, or incompletely dominant. A dominant gene is one that is expressed in the offspring regardless of whether the matching gene on the homologous chromosome is identical to it (i.e., it is homozygous for the dominant gene), or is a different allele (i.e., it is heterozygous for this trait). A recessive gene is expressed only if both copies of the gene are identical (i.e., the individual is homozygous for the recessive gene). If a heterozygous individual has a different appearance (phenotype) than either of the two types of homozygous individuals, and if all three possible combinations of alleles is expressed differently, that trait is said to show incomplete dominance.

 

This issue is complicated, since more than two different types of alleles may exist for a given type of gene (though a single individual can only have two of them). Such a series of alternative gene forms (called multiple alleles) control some aspects of coat color in dogs. Some traits are controlled not just by a single gene, but by several genes located on the same or on different chromosome pairs. Such polygenic traits include body size and many types of inheritable diseases or defects.

 

The genotype is the genetic composition of an individual, and refers to whether it is homozygous dominant, heterozygous, or homozygous recessive for a given gene. The phenotype is the physical expression of the individual's genes; it includes both visible obvious physical characteristics, (such as size, coat color, shape of ear), and also physiological/chemical traits (such as blood type, presence or absence of certain enzymes, and a tendency to develop certain tumors).

 

If a genetic disease is caused by a dominant allele, any dog or puppy that has even one copy of the dominant allele will show the disorder. This type of disorder is easy to eradicate, since every individual carrying the gene shows the disorder. These dogs can be eliminated from a breeding program. But if an inheritable disorder is caused by a recessive gene (which is more often the case), the disorder will only be expressed in a homozygous puppy whose parents both carry the abnormal recessive allele and who both transmit it to that pup via egg and sperm. If the puppy receives one normal allele from one parent and one abnormal gene from the other, the puppy will be heterozygous and the dominant normal allele covers up the presence of the recessive gene. The puppy will not be affected, but will be a carrier for the genetic disorder, passing the abnormal recessive gene on to about half of its offspring.

 

Because heterozygous carriers of a recessive gene do not show the trait in their phenotype but pass it on to about half of their offspring, recessive phenotypic traits may appear to skip one or more generations, reappearing when least expected. When a carrier mates to another carrier, each passes on a copy of the recessive gene to produce a homozygous-recessive offspring. To control the spread of a harmful recessive gene in Leonbergers, it is necessary to identify the carriers, since culling just the affected puppies displaying the undesirable trait does not get rid of the gene or its unaffected carriers it only eliminates the homozygous-recessive puppies.

 

Genetic changes (mutations) may occur naturally or be triggered by environmental factors such as exposure to drugs, chemicals, pollutants, and X-rays. Mutations include tiny changes in the structure of a single gene (which can cause major and oftentimes harmful changes in the phenotype). They also include major alterations in the structure of a chromosome, visible with a microscope. A chromosome may be lost (so that one member of a pair is missing) or an extra chromosome may be present (so there are three or more of a given type of chromosome instead of a pair), or a chromosome is missing a piece of itself (or a piece that is present in duplicate). Fortunately for breeders, most large chromosomal defects are fatal early in development (thus not a major problem).

 

When one considers that an Leonberger is a vast complex of structures within structures, a unique individual dog unlike any other, it becomes clear that serious breeding is more than just mating a male with a female. DNA makes up the genes, genes make up the chromosomes, chromosomes make up the nuclei of the cells, and the millions of cells that make up the whole dog are the science of dog breeding responsible for the design of an Leonberger. Further reading is recommended for those who take seriously the science of dog breeding.

 

GENOTYPE AND PHENOTYPE

 

A dog's phenotype appearance does not always tell you what makes up its genotype, since all dogs carry many recessive genes that are not expressed (because these genes are paired with dominant alleles). Recessive genes produce normal and desirable traits as well as some harmful ones  (just like dominant genes). Emphasis should be placed on a dog's genotype because you must know what genes a breeding pair carries to help ensure that you breed quality Leonbergers free from faults and inherited disease. Look closely at the parents, grandparents, brothers, and sisters--even the great great grandparents--to help predict what you will be producing. Study the pedigrees of the dogs you plan to breed, and become familiar with the names of their ancestors and close relatives. If your dog's ancestors are still living, try to personally see as many of them as possible. If this is not possible, contact their breeders or owners for photographs of the related dogs and ask about any health problems they may have had. Take the time to discuss your breeding plans with the breeders of these lines; their experience can be invaluable.

 

Best results are likely to occur when a phenotypically ideal dog is a product of a genotypically ideal breeding, and subsequent breedings have proven the dog is prepotent to pass on its desirable attributes. One disappointing lesson many breeders have learned, however, is that their ideal Leonberger does not always reproduce itself. That is because it passes on only one of each pair of genes to each puppy, and some of those genes may not be the best members of the pair.  Additionally, a puppy can be ruined by a careless owner who either over feeds, does not feed an adequate food, does not provide exercise or forces a puppy into too much physical activity—the injurious combinations are endless.

 

LINEBRED, INBRED AND OUTCROSS BREEDING

 

You should also be familiar with the terms linebreeding, inbreeding and outcrossing. Linebreeding is the mating of dogs with common ancestors in the second and third generation (grandmother to grandson, grandfather to granddaughter). This is the most common type of breeding used by serious breeders. Linebreeding offers a large gene pool of related animals to choose from, fixing and reinforcing type. It also helps expose the presence of harmful recessive genes in carrier parents by allowing them to produce homozygous recessive puppies that show the undesirable trait. Faulted dogs can then be eliminated from a breeding program by spaying or neutering. The superior dogs are then carefully linebred to help guarantee type and predictability in the line.

 

Inbreeding is the mating of closely related dogs (brother to sister, father to daughter and mother to son). Inbreeding emphasizes and strengthens both positive and negative traits. It is the most expeditious way to determine which recessive traits are dormant in your line. One problem in "fixing" a genetic trait in inbred Leonbergers is that if the trait is undesirable, it will be extremely difficult to breed out of your line. Actually, the number one reason why dogs are destroyed is due to personality disorders, and most of those can be traced to the fact they were inbred, according to Dr. Kurt Matushek of the American Veterinary Medical Association.

Inbreeding produces animals that acquire the same allele from both parents as a result of their common ancestry, meaning it increases the number of genes that are homozygous. Inbreeding holds many potential problems--it does not discriminate between good alleles and bad, therefore continuous inbreeding is just as likely to assemble genes homozygous for bad alleles as for good ones, warns Dr. John B. Armstrong.  

Deleterious genes become widespread and the breed loses vigor. For example, inbreeding to fix a desirable trait makes it more likely individuals will also inherit the same set of genes for the immune system from both parents, and be born with less vigorous immune systems. Nature goes to great lengths to discourage inbreeding. In nature, related animals rarely mate, preventing genes for diseases and defects from coming together with frequency. Wild canids have a variety of behaviors designed by nature to eliminate or severely restrict inbreeding.

 

Outcrossing is the mating of unrelated dogs based on phenotype. For example, if your bitch lacks good bone and needs improvement in head type, breeding to a male with good bone and a good head type might improve on her faults, if the male is prepotent for these traits. Clearly, outcrossing is more of a gamble than linebreeding or inbreeding.

 

Selective outcrossing can result in improvements in the progeny of linebred or inbred dogs when these dogs do not have the desired trait within their genetic composition. Understanding the prepotency of the dogs to which you outcross is the only sensible way to decide if  it will improve your line or breeding program. Outcrossing is the least predictable way to breed but, occasionally, a breeding pair will produce a litter of Champions. After you repeat the breeding you may find you have another litter of Champions. The outcross sire and dam will consistently produce good quality, Champion Leonbergers, this is called a nick.

 

The formation of a breeding program usually begins with linebreeding or outcrossing dogs. The objective is to discover where improvement is needed. You may find, for example, that your Leonbergers lack strong rears or straight fronts. The logical step would be to introduce into your breeding program linebred dogs that are proven prepotent in these areas. Once you have attained some measure of consistency for one or two generations, you can then outcross.

 

A responsible breeding program takes study, time, and most importantly, patience. When the puppies have matured a breeder can fully evaluate the results of a breeding program (and one litter does not make a breeding program). Soundness of puppies and absence of inheritable health problems should be a major consideration.

 

Keep accurate records of each breeding, including size of litter, number of stillborn pups or puppies that die young, and the reasons for the deaths. Keep a file folder for each litter and take photos of each puppy at varying stages of growth. Include in the folder photos of the sire and dam, pedigrees, and placement information. Also, keep in touch with puppy buyers so you can keep records of any inheritable health problems that may develop later in the dog's life.

 

Kennel blindness is the biggest reason for lack of breeding success. Be honest with yourself; you must be able to critique your dogs with total objectivity. If you refuse to see the faults in your stock, you cannot possibly correct them. Do not get hung up on one facet of a dog (such as head type or ear size) at the expense of other important physical and temperamental qualities. Plan your breeding program to produce superior temperament and good health, then structural soundness, balance and good movement."

Excerpted and adapted from: "Akita-Treasure of Japan, Vol. II (c)

 

After considering the complexities and problems of breeding healthy show quality Leonbergers with correct temperaments, it is easy to admire those breeders who experienced successful results when correctly mixing genotype and phenotype. In my experience, these breeders are always honest and forthright about their ideas and methods, making them wonderful mentors for the novice breeder.

The links on the right take you to websites that tell you about the genetic screenings each breeding pair should undergo.  The LCA requires all breeding Leonbergers to undergo these screenings before they are bred.  No other organized group or individual requires these screenings, which is why you should educate yourself then request proof of certifications before you purchase the puppy.

 

Keep in mind that not all Leonbergers need to be bred.  The most responsible and respected breeders within the dog world are those who do not breed unless they have a list of potential puppy buyers waiting for a puppy.  To have 4,5, 6 or more six-month old Leonbergers waiting for someone to purchase at least one of these dogs is my idea of a nightmare! The most important, formative stages of puppy training cannot be accomplished with that many unsold puppies.  That’s not breeding—that is self-destruction!

(c) Copyright 2000 Barbara Bouyet

 

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Last updated 02/01/2010 .

© 2004 All Rights Reserved.

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