Has your apparently healthy Labrador retriever seemed uncoordinated or suddenly collapsed following five to 15 minutes of strenuous exercise? If your dog suddenly appears wobbly in the real limbs and appears unable to get up, then you could be dealing with a syndrome described as “exercise-induced collapse (EIC) in Labrador retrievers.”

Since it was first described in 1993, the syndrome has been blamed on heat intolerance, low blood sugar, cardiac arrhythmias or even the possibility of a metabolic myopathy. Researchers have recently detected a gene mutation, “dynamin 1”, involved in the development of exercise-induced collapse. Dynamin 1 is an important gene involving synaptic transmission. A defect in this gene results in a lack of communication between nerves and the muscles of the body. The mode of inheritance appears to be autosomal recessive with most dogs being symptomatic for the mutation found to be homozygous (having two identical codes) for the gene. Two breeds closely related to the Labrador retriever; the Chesapeake Bay and curly-coated retriever, have also been found to harbor the gene mutation.

EIC causes affected Labrador retrievers to lose control of their hind limbs following intense hunting or other intensive physical activities the breed is routinely trained to perform. The dynamin gene 1 plays an important function during synaptic transmission. The mutation results in the diminished communication between nerves thereby resulting in synaptic interruption during intense exercise. The muscles go limp because they are not receiving adequate information concerning when to contract.

Affected dogs may be any color (black, yellow, or chocolate), and most are from field-trial bloodlines. These animals tend to be extremely fit and muscular with an excitable temperament and lots of retrieving drive. Most dogs will appear to be normal mentally while still others will appear dazed or confused during an attack. Individual dogs do not appear to be in pain but are rather anxious to continue the activity they were originally involved with. Although considered unusual, dogs have died during a collapse episode. Most dogs with Exercise Induced Collapse recover without showing any laboratory abnormalities and typically recover completely within 5 to 25 minutes.

Complicating environmental factors include excessive heat and humidity.

Dogs affected by EIC may continue their lives as normal pets but characteristically are unable to handle the stress involved with intensive exercise and training necessary for field trials.

Treatment with Phenobarbital or other sedative drugs may decrease the dog’s level of excitement or stress necessary to induce an episode of collapse. Other affected dogs appear to get better with age or after being neutered.

Up to 30% of all Labrador retrievers are believed to carry the dynamin 1 mutated gene, while 3 to 5% of the Labrador population is believed to by symptomatic of EIC. The University of Minnesota’s College of Veterinary Medicine (UMCVM) is able to offer genetic testing and counseling from blood sample testing.

References:

Hoskins, Johnny. “Exercise-induced Collapse in Labrador Retrievers.” DVM. October 2008. Pp. 8S-11S.

Veterinary Practice News. Vol. 20, No. 11. November 2008. P. 4.