Exercise Induced Collapse in Labrador Retrievers

Debra Folsom

Work recently published (2008) at the University of Minnesota has identified a gene mutation in Labrador Retrievers associated with Exercise Induced Collapse. The gene mutation is predominately found in field bred Labradors. Affected dogs may collapse after five to fifteen minutes of exercise usually involving hunting or retrieving where there is some level of excitement for the dog. Dogs show muscle weakness and will often drag their rear quarters as they attempt to continue activity. Not all episodes of collapse in Labradors is due to EIC. Overheating (hyperthermia) during exercise or episodes of low blood sugar (hypoglycemia) may cause similar symptoms resulting in collapse.

A genetic test for the mutant gene is now available through the University of Minnesota. EIC appears to be a genetically simple trait that is due to a mutation in just one of the approximately 20,000 genes present in a dog’s genome. Their research has identified a mutation in the canine dynamin 1 gene. The dynamin 1 protein encoded by the DNMI gene functions to maintain neural and neuromuscular transmission during high intensity stimulation. Thus, a DNM1 mutation that affects the function of the dynamin 1 protein could logically explain the physical and downstream clinical signs associated with EIC episodes. Dogs can be tested by sending a simple cheek swab of the dog’s saliva to the University Lab. Dog owners can collect the sample easily themselves without the help of a veterinarian and submit the sample by mail to the University. For complete information on EIC and how to test your dog, go to the University web site at: http://www.cvm.umn.edu/vdl/ourservices/canineneuromuscular/home.html. They prefer you use a sterile swab that you can obtain from your veterinarian or a pharmacy. You need to submit two samples for each dog.

Many owners and breeders of field Labrador Retrievers have been testing their dogs and it appears that a large number of dogs tested are carriers of the gene. Carriers have one copy of the mutated gene and one normal copy of the gene. They are unaffected by EIC but when bred have a 50% chance of passing on the normal copy or the mutated copy of the EIC gene to their offspring. Dogs that test “clear” of the EIC gene have two copies of the normal gene and cannot pass on the EIC gene to their offspring. EIC “effected” dogs have two copies of the mutant gene and will pass that gene on to 100% of their offspring. It is important to note that not all dogs with two copies of the EIC gene, or test “affected”, display EIC symptoms. Some dogs although they test “effected” never have collapsing episodes.

It appears to me after talking with other breeders, observing test results of dogs advertised on the internet and conducting tests in our own kennel, that as many as 60 -70% of our best Field Champion lines of Labrador Retrievers in the U.S. may be carriers of EIC (one copy of the EIC gene). Another 10 – 15 % may be affected (two copies of the EIC gene), with the remaining 15 – 20% testing clear. As reputable breeders, genuinely interested in the perpetuation of sound, working Labrador Retrievers, what do we do with this information? It is simply not practical to eliminate all EIC carriers from our breeding pool of

dogs since many of these dogs carry desirable traits that have taken several generations to produce. Since carriers or affected dogs can be bred to clear dogs without producing dogs with EIC symptoms, that is certainly a viable option. I believe the first line of defense is to test all breeding dogs so we at least know what we are doing and what the most likely outcome in the offspring will be. This malady did not get into our field Labrador gene pool overnight and will take time to effectively breed out of our dogs. At our kennel we replaced our studs with only dogs testing “clear” for EIC . These dogs can be bred to carriers or affected bitches without producing any affected offspring. As we gradually retire breeding bitches, we will replace them with EIC clear individuals, eliminating the mutant gene from our breeding stock completely.

Many breeders breed for pets or hunting dogs, where very few of the offspring will ever be bred. Puppies that go to individuals that may want to breed their dogs can be tested as puppies before they are sold. It is important to not over react if your dog tests as a carrier or even affected. These dogs can still be bred to clear dogs and produce puppies that will not have EIC but are simply carriers of the gene. Also remember that not all dogs that test as “effected” exhibit symptoms of EIC. It is important that two carriers, not be bred together or a carrier bred to an affected dog. These combinations will produce dogs with EIC. Thus testing of all breeding stock is essential if we are to breed our way out of this recessively inherited genetic abnormality. Information is key to making sound breeding decisions that will benefit future generations of Labradors.

It is important to note that EIC is not a death sentence for affected dogs. Symptoms may be managed or reduced in many dogs. The best treatment in most dogs consists of avoiding intensive exercise in conjunction with extreme excitement and ending exercise at the first sign of weakness/wobbliness. A few dogs have, however, responded to medical treatment to the degree that they can re-enter training and competition at a high level. There are now numerous reports of severely affected dogs improving when they were treated with Phenobarbital (2 mg/kg every 12 hours or every 24 hours). In some cases “sports drink” type electrolyte solutions formulated especially for dogs and administered before periods of exercise have been helpful in controlling episodes of collapse. Dogs often improve with age as their level of excitement and exercise is reduced.

We should not try to eliminate EIC from the Labrador gene pool quickly or all at once and “throw the baby out with the bathwater” so to speak. Eliminating all EIC carriers from the gene pool all at once will result in erasing many of the great, positive characteristics that have taken years to develop in our best dogs. Proceeding carefully and slowly from here armed with information through EIC testing will bring on the best breeding results in the future.

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