A breeder generally becomes aware of a genetic disease when one or more of the offspring they produce develops a defect. Many breeders choose to erroneously accuse the stud or bitch owner, or dogs in their background as the only culprits. The fact of the matter is genetic diseases are common in purebred dogs, this means dogs from BYB to well known respected breeders. A great majority if not all dogs carry 4 to 5 defective genes. Yet armed with these figures, breeders are still afraid to claim they have defects, this is why genetic diseases are so common in purebred dogs. There are registries such as the Orthopedic Foundation for Animals (OFA) and the Canine Eye Registration Foundation (CERF) which assign numbers to "normal" animals. Very few breeders are willing to register an animal they know have/had defects, thus giving the illusion to the public that the majority of dogs are normal, and few have defects. The reality is that there are a lot of dogs with genetic diseases, we just don't hear about them, and breeders tend to not talk about them. Out of the 42,000+ Danes registered in a 5 year period (1998-2003) with the AKC, only 2,000 have had results of any OFA hip testing done, with only 8 breeders registering animals showing results of hip dysplasia (as of 2003). I do not believe there are many breeders that intentionally set out to whelp defective dogs, but I do believe breeders are using animals they know would not pass a standard test. The first step towards helping eradicate diseases is honesty from the breeder to themselves, and other breeders. They MUST know the defects in their lines and offspring produced. Also keep track of animals sold with breeding right. Document defects in their litters, after all, 50% of the offsprings genes came from you. Breadth of pedigree is much more important than depth of pedigree in tracking diseases. The second step is to develop a genetic pedigree of these defects. We will include one of our genetic pedigrees to explain how they are made. The third step is to prioritize your defects. Classify them as major or minor. Major being defects that will affect the health, and eventually cause premature death in the dog. The fourth step is to first if possible, establish the mode of inheritance. Many diseases have no known mode of inheritance. If the mode is known, breedings can be planned accordingly, once again, you MUST know the genetic background of what you want to breed to in order for this to be effective.
AUTOSOMAL RECESSIVE INHERITANCE: Carriers of recessive genes cannot usually be detected except by producing affected offspring. Puppies get one gene from each parent, making both Sire and Dam proven carriers. Parents will appear normal without the defect.
AUTOSOMAL DOMINANT INHERITANCE: Both parents do not have to have a gene for the disorder to cause the trait to occur, but one parent must show the trait in order for it to occur in their offspring.
SEX-LINKED TRAITS: They are nearly always on the X-chromosome. The distinctions between recessive and dominant traits also apply to sex-linked traits.
POLYGENIC TRAITS: More than one gene is needed to produce the defect. Both the Sire and Dam contribute one or more genes to cause the defect in the offspring.
This is one of our 4th generational pedigrees. At the top you start with generation 0. Squares depict dogs, circles depict bitches. A line from dog to bitch indicated a breeding, with offspring placed below. You can make any key you like to denote which circles and squares apply to which animal. We have used numbers 1 through 5 for dogs and 1 through 4 for bitches. The number next to each breeding line is when the litter was whelped.
You want to make copies of this pedigree as you will use it in the future to add on any defects. Many breeders work on one trait at a time with genetic pedigrees as they can get confusing when adding multiple defects. We have always used the multiple defect pedigree as it gives a total picture of what has occured. You may want to start a new pedigree for outcross breedings as you will want to assess that dogs background also.
Below is the pedigree after filling in all the defects. Remember, you must fill in ALL defect including the minor non-life threatening ones, to get a clear picture of what is going on in your breedings. You may refer back to our genetics page to determine diseases found in Great Danes.
You may use any key to denote defects, we have used a combination of letters and numbers below each dog displaying a defect. The 2 letters above each affected animal lets us know what body system was affected. Affected animals are shaded in totally, carriers (if known) are half filled in. Crosses below animals indicate death before 10 days of life, a line through a animal indicates they are deceased. An arrow under an affected animal means that this is the first known case of the disease. Do not be overwhelmed once you do this. Remember, both major and minor defects are studied. Keys are necessary for anyone else to be able to read your genetic pedigree.
We will demonstrate how it works now. Look for the litter born on 2000, out of bitch #4 and dog #4. The first puppy is a square, his defect was A1 which on our key means deaf. The HB above refers to "hearing/balance", the line through him indicates he is deceased. Puppy #6 is a dog, his defect is A2, which means wobblers syndrome, the SK indicates "skeletal", since wobblers mode of inheritance is polygenic, both Sire #4 and Dam #4 are carriers for the defect, they are half shaded in. This is where a breeder can decide who to breed together, and who not. Just because a defect has been noted does not mean you cannot breed the parents. If you look at dog #3, he was bred to bitch #3, and #4 and produced the defect L, C1, and C8, all are occular defects. They are ectropion of the lower eyelids and protrusion of the 3rd eyelid. He is also the Sire of dogs #5 and bitch #4, who in turn have produced the same defect in their offspring. In our outcross line, this defect is also being repeated with Sire #3 use, and some of his offsprings use. This is not a life threatening condition and is cosmetics. This is our main defect we are seeing now. It appears to be a recessive gene. With any defect, you want to monitor frequency. If a defect appears only once and both the Sire and Dam have not produced it again, it is not something to be too alarmed about. These defects do occur, document them, monitor for them, but concentrate on defects that are replicating. Remember to place value on defects between minor and major, working on any major ones first.
Here is a completed 4th generation genetic pedigree with all outcross litters added in.
Genetic pedigrees are wonderful tools to get a total picture of what defects are being produced. If breeders were able to exchange them, breedings could be planned accordingly. Carriers would not be bred together, and other defects could be examined for frequency between animals. The goal of every breeder should be to produce healthy dogs first, then all else can fall into place.
If you would like assistance in producing a genetic pedigree, please do not hesitate to e-mail me.