What Iditarod sled dogs tell us about intensive exercise:
The 2005 Oscar W. Schalm Lecture
And you thought you had a strenuous day.
Iditarod sled dogs race across two mountain ranges, a frozen sea and snow for 1,100 miles, run an average of eight miles per hour for more than a week, eat 12,000 calories a day and expend four times the energy that Lance Armstrong burns during the Tour de France bicycle competition.
Students and faculty of the School of Veterinary Medicine learned more about the health of these elite canine athletes May 16 when veterinarian Michael S. Davis presented "Racing Sled Dogs and the Physiology of Sustained Strenuous Exercise." An associate professor at the Oklahoma State University Center for Veterinary Health Sciences and director of its Equine Athletic Performance Laboratory, Davis gave the talk as the Oscar W. Schalm Lecturer for 2004-2005.*
In humans, sustained exertion can lead to a "cornucopia of maladies," according to Davis. Describing his research work as "following data and opportunity," Davis has observed Iditarod sled dogs as models for human health conditions since 2001. His work touches on the development of asthma associated with skiing, gastric ulcers and other conditions that affect both canine and human athletes.
Davis said that Iditarod race organizers provide more than twenty checkpoints where volunteer veterinarians conduct a variety of inspections on the more than 1,400 competitors. His research studies take place on selected animals in cooperation with mushers, the sled dogs' owners and trainers.
Davis' research takes place in the unique "laboratory" of the Iditarod race course. Using an especially outfitted and self-contained veterinary laboratory on wheels, Davis and a team of veterinary physiologists have gathered data with basic monitoring: blood tests and endoscopic examinations.
Among the team's findings, Davis reported that blood tests taken over the course of many days show signs of progressive anemia in the animals. The single most likely reason for the anemia in these dogs is the formation of multiple bleeding stomach ulcers in the dogs. The ulcers can be prevented with the daily administration of gastric antacids, which should prevent the dogs from becoming anemic in the future.
At a subclinical level, Davis' researchers found that up to 35% of dogs examined showed some evidence of gastric ulcers, a much higher incidence than in normal dogs. Davis credited Dr. Mike Willard (gastroenterologist at the Texas A&M University College of Veterinary Medicine), and his video endoscopy system for enabling researchers to examine 42 dogs in a single day during the 2005 Iditarod.
The team has also conducted a prevention study demonstrating that famotidine (the active ingredient in Pepcid), when mixed into the animals' food, eliminates gastric ulcers without affecting the dogs' appetites. Six of the 10 top finishers, including this year's winner, showed significant improvement with the famotidine acid suppression therapy. One key advantage to the drug, reported Davis, is that mushers don't need to remove their mittens to pill their dogs. This "convenience" becomes critical when temperatures hover at 35 degrees below zero.
Unexpectedly, not one animal sampled has had signs of hypoglycemia, or low blood sugar. More research is needed, Davis said, to verify that the animals use ketones rather than glycogen, a stored source of carbohydrates in the liver, to sustain themselves during racing. Also in contrast to findings in human endurance athletes, Davis stated that the canine immune system appears to be well maintained during sustained exercise.
Extremely low temperatures do appear to cause similar respiratory responses in the lungs in both dogs and humans, though sled dogs examined showed no outward signs of asthma.
Michael S. Davis, a diplomate of the American College of Veterinary Internal Medicine, conducts comparative veterinary research on the effects of sustained strenuous exercise on the body. He has a particular interest in studying the reactions of airways to strenuous exercise under cold conditions. His group studies horses and, more recently, sled dogs. Ongoing projects seek to explain the mechanisms of exercise-induced disease as a first step toward developing new treatments and prevention strategies.
Funding for Davis's asthma research comes from the National Institute of Health, and sled dog owners have supported the studies on gastric ulcers. The Defense Advanced Research Projects Agency (DARPA) has also funded comparative studies relevant to human endurance exercise.
*The Oscar W. Schalm Lectureship, established in 1988, honors the memory of Oscar W. Schalm, a founding faculty member known for his investigations of bovine mastitis and the exercise physiology of horses as well as his expertise in hematology. The Lectureship promotes a tradition of scholarship, service and commitment to veterinary medicine and recognizes the lecturer's distinguished contributions to the profession.