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Genetic Health Testing

Genetic Testing

Many of the inheritable diseases require that both parents pass on a copy of the gene responsible for disease to a puppy.  To avoid breeding dogs that could pass on these genes and have affected puppies, one or both parents are genetically tested.  The following are some of the most common diseases that Labrador Retrievers can and should be tested for prior to breeding: 

Exercise Induced Collapse - EIC was first identified in the 1990s, but since then, it’s been seen increasingly in Labrador Retrievers. Because litter mates and other related dogs were found to be similarly affected, veterinarians came to understand the hereditary nature of the condition. It’s since become clear that the exact source of the genetic problem involves a mutation in a gene involved in the communication between nerves of the central nervous system. In EIC, dogs will collapse after 5 to 10 minutes of high-drive, trigger activities, such as chasing a ball or hunting. Though a large majority of these cases recover completely within a short timeframe (less than 30 minutes), some dogs have been known to die of the condition.

Canine Degenerative Myelopathy (DM) - "DM has a typical age of onset in affected dogs from 7 to 10 years of age. The first clinical signs of DM often noticed by owners are related to non-painful weakness in the hind limbs. Affected dogs will have difficulty getting up after laying down and have a general loss of balance and neurological function in the hind limbs resulting in an abnormal gait and dragging of the hind feet. After the onset of clinical signs, the weakness witnessed in the hind limbs gradually expands to incorporate the front limbs. In late stages, dogs can lose bladder and bowel control and will eventually be unable to walk. The progression from the first clinical signs to end stage disease typically occurs over a 6 month to 2 year period. There is no cure for DM and treatments are palliative at best." Paw Print Genetics

Labrador Centronuclear Myopathy (CNM) - "Unlike the late-onset of DM, the onset of the muscular disease known as centronuclear myopathy (CNM) typically occurs in young Labradors between 6 weeks and 7 months of age. Similar to DM, CNM is a disease that will greatly affect a dog’s ability to work or perform physical tasks. Affected dogs typically display an intolerance to exercise, a hopping gait, decreased reflexes, generalized skeletal muscle weakness and atrophy, and an increased likelihood of collapse when in cold temperatures. Many affected dogs also develop a loss of muscle contraction in the esophagus (megaesophagus) resulting in difficulties swallowing. Problems with swallowing can allow food particles and other material to enter the lungs, thus, leading to severe pulmonary infections known as aspiration pneumonia. CNM tends to progress in severity until stabilizing at around 1 year of age. However, affected dogs do not improve and will continue to have problems often requiring medical intervention throughout their life, especially in relation to respiratory disease. Dogs obtaining medical interventions when necessary can have a normal lifespan despite their abnormal physical status. However, there is currently no cure or effective treatment for CNM." Paw Print Genetics

Progressive Rod-Cone Degeneration (PRA-PRCD) - Progressive retinal atrophy (PRA) is a category of different progressive conditions related to ­retinal atrophy that can eventually lead to blindness.  Progressive rod-cone degeneration (PRA-PRCD) is one specific type of PRA that affects many dog breeds.  It is an inherited eye disease with late onset of symptoms that are due to degeneration of both rod and cone cells of the retina.  These cells are important for vision in dim and bright light.  Most dogs begin to show symptoms of the disease at approximately 3-5 years of age that manifests as difficulty seeing at night (night blindness) and loss of peripheral vision.  Although rate of onset and disease progression can vary by breed, PRA-PRCD typically results in eventual loss of sight and complete blindness in affected dogs.  

After Genetic Testing

A dog carrying one copy of a defective gene is not taken out of the breeding stock if he/she is clear of all other defective genes and conforms to the Breed Standard.  While "clear by parentage" is the ultimate goal of genetic testing breeding stock, there are always other considerations (for example, limiting the gene pool by too selective breeding which can lead to new diseases that are inheritable). 

A carrier of any of the above named diseases can be bred to a non-carrier; none of the puppies will be affected by the disease as it takes two copies of the defective gene for the disease to manifest.  Some of the puppies will be carriers but not be affected by the disease.  Puppies born to a dam and sire who are both clear of any defective gene for any of the diseases named will be deemed "clear by parentage".   

What about the things for which there is no genetic test available?

While all responsible breeders test for the genetic diseases relevant to their breed and/or required by their Breed Club or the AKC; not every disease or disorder has an available test. Just like with human beings, sometimes something can go wrong and while there is a potential of that "something" being genetic or inherited, there just simply isn't a test for it yet or even enough evidence to suspect that it is "genetic". 

The following diseases appear to be inherited but only a repeated appearance/pattern of affected puppies born to a breeding dog/pair can alert Breeders to an issue. Pedigree study is limited to what documentation is provided.  

  • Cancer
  • Epilepsy
  • Patella Luxation (Research ongoing)
  • Congenital Heart Anomalies
  • Tricuspid valve malformation
  • Canine hypothyroidism
  • Atopic/Allergic Skin Disease

Congenital Defects: Just like in humans, sometimes something can go wrong during gestation that affects one or more puppies.  Exposure to some form of a toxin can cause birth defects; positioning in the uterine horn in a large litter can affect the development of a limb or the tail, an excess or deficiency in, for example, Vitamin A during gestation can cause developmental issues (i.e. an undeveloped leg or a crooked tail) in one puppy but not in the entire litter. 

Puppies can be born showing a recessive trait like a shorter tail or a longer tail than we are used to seeing and some puppies are born with mis-markings - a white spot or line on their chest, a white foot, and so on because Labradors, like all pure bred dog breeds, originated from the mating of different breeds to produce a new breed.  

When should a dog be removed from a Breeding Program?:

When there is no genetic test available, a dog or a bitch will be removed from a breeding program if a pattern emerges among the off-spring of that dog or bitch. A pattern meaning that multiple offspring suffer from one particular issue indicating a possible genetic component and not random accidents of nature.   Responsible breeders welcome information from their puppy owners about illnesses puppies from their breeding program may present.  The information allows them to keep notes on each litter and each Dam and Sire used in those breedings to determine if there may be an issue.  For example, if a breeder uses two unrelated bitches in their program and the same Sire for repeat litters in which there emerges a pattern, it is a simple matter to determine that it is the Sire and not the Bitches who may be passing on an undesirable trait or predisposition.  On the other hand, if one Bitch bred to different Sires has a pattern in her offspring, then the issue is with the Bitch. 

Responsible breeders do not breed a dog with either a history of any major illness itself or who was born with a congenital (present from birth) issue.  For example, a Bitch or Dog diagnosed with allergies or immune issues (Chronic Demodectic Mange) should never be bred nor should a puppy born with a crooked tail be bred. While these issues may be inherited, that has yet to be proven, but good breeders take no chances.  

Many times, a young puppy is diagnosed with some sort of immune issue and their owner will be told by their Vet or by others on the internet that they should tell the Breeder to remove one or both parents from the breeding program.  Demodectic Mange is one example (there are two forms of Demodectic Mange - localized and chronic), yet, there is no real evidence that this is genetic/inherited in any breed other than Boxer or Argentinean Mastiff and mixed breed dogs.   While a gene may eventually be discovered that can be used to test breeding stock, there is, at this time, ample evidence that this is an issue stemming from an immature and overstressed immune system in individual puppies.  

Localized Demodectic Mange (also called Juvenile Demodectic Mange)  manifests typically AFTER the second or final round of vaccinations indicating that it is caused by an overstressed and immature immune system.  All dogs have mites but typically, the maturing immune system deals with the issue keeping the mite population at a managable level.  Every now and then something goes awry. Eighty-five percent of localized Demodectic Mange is diagnosed in young puppies!  The last born in a litter and the less aggressive nursers during the first 12 - 24 hours after birth and the runts of any litter appear more likely to be diagnosed with it  because these puppies have less of their Dam's immunity passed to them in the all important first 12 - 24 hours after birth. 

This is a good time to discuss the rush to use steroids in treating puppies.  NEVER allow your Vet to prescribe steroids to your puppy without first doing diagnostic testing (like cultures) to determine the issue and ONLY after non-steroidal treatments have failed to eliminate the issue - Get a second opinion if your Vet rushes to steroid use without first doing cultures or other treatment.  Steroids depress or stop the immune system which can lead to secondary issues developing (bacterial infections for example) which can lead to the need for even higher doses of steroids; steroids must then be slowly discontinued in the hopes that the immune system "restarts/resets".