"You can lead a horse to water, but you can't make him drink." You can put a pan of water in front of a dog, but that doesn't mean he's been "watered." It doesn't matter how much water we set in front of our animals. What matters is how much water we get INSIDE of our animals.
Sled dogs need water, and lots of it. Over the course of 10 to 15 days, the Alaskan sled dogs and huskies racing the Yukon Quest will require roughly 6 liters (or quarts) every day. That's 1.5 gallons of water for a 50-pound dog. A 150-pound human would have to drink 4.5 gallons, or 72 glasses, of water every day to keep up.
A musher simply can't pour a quart of water in front of every sled dog on their team every four hours. Not at 40 below! If their dog doesn't drink it right away, the water will freeze. And, most huskies won't drink plain water in the winter, anyway. The ones that do have to be conditioned by the musher to it over time. And, even those who are conditioned won't drink a quart all at once.
So, how do sled dogs get their water? After all, water is the most important substance on Earth for supporting life. That's why astronomers are always looking for planets with evidence of water. And, that's why veterinarians continually monitor racing huskies for their hydration status before anything else. A sled dog's body is 70% water. No water, no dog.
Dogs and people consume their daily water in three different ways: Free-choice, pre-formed, and metabolically.
Free-choice water is the stuff that comes out of the tap and into the drinking glass. It's one of the most important ways humans consume water year round. Dogs also get most of their water free-choice in the summer, when they take that long cool drink out of their water dish or a clear mountain stream. However, in the winter, free-choice water is hard to find. The streams are frozen and most dogs won't drink water cold, anyway. (I must be part husky because I won't drink cold water in the winter, either.) Free-choice water in the winter is a cold pill to swallow.
However, the second important source of water for a racing sled dog, and a human, is pre-formed water. This is the water that is part of the food itself. For instance, if you take a crisp vegetable dinner salad and dehydrate it, most of the pre-formed water will evaporate and you'll be left with a dusty pile. The same goes for meat, fish, fruit, and dairy products, etc. And, if you read the label on that can of dog food, you'll see it's also mostly water.
Sled dogs eat their meals as a soupy gruel of various meats, fowl, and/or fish. Even the dry kibble mixed in has a small percentage of moisture content, plus the broth water it soaks up in the cooking process. Treats along the trail, such as chunks of moist frozen meat or fish, also are full of water. The closest thing to free-choice water is the warm broth, often made with the leftovers of a meal, slurried with more water. In the winter, over 80% of a sled dog's water intake will come in a pre-formed manner. The dogs don't drink water so much as they eat it.
The remaining water supply, up to 20%, comes in the form of metabolic water. When fats in the diet are broken down for energy, oxygen is combined with the carbons and hydrogens of the fatty acids to make carbon dioxide, which is exhaled, and water, some of which is retained by the body. In other words, a portion of the water the dog "drinks" is actually the result of a chemical reaction in the dog's body as it burns up food for energy.
Humans don't derive much water metabolically because we don't (or at least shouldn't!) eat a lot of fat. But sled dogs are equipped with a much more efficient method of converting fat to energy. Racing marathon dogs can consume up to 60% of their dietary calories as fat. That's between 8,000 and 12,000 kilocalories per day. (A kilocalorie is a thousand little calories.) The equivalent amount for a 150-pound human would be approximately 50 Big Macs per day.
Of course, dogs don't have opposable thumbs and they can't operate the TV remote control. So, sled dogs running 100 winter miles per day can thrive on such a lard-laden diet where human couch potatoes never could -- although more and more of us are trying.
What about snow? There's certainly enough of it up here in the North. There are three reasons why most sled dogs are not allowed to eat snow--we call it "dipping," "grabbing," or "scooping." First, unless the husky is a Fred Astaire on paws, it runs the risk of stumbling and hurting itself as it tries to grab a mouthful of fresh snow on the run. And, it throws off the rhythm of the teammates. This is especially important as the speed of the team increases.
Second, snow is mostly air. While nearly-melted snow will be 100% water, freshly fallen mountain snow can be 5% water with air trapped among the crystals. That is, if you melt 20 inches of fresh snow you'll get as little as one inch of water. So, if a racing marathon sled dog needs to consume six quarts of water per day, it would have to eat 120 quarts, or 30 gallons, of freshly fallen snow every day to get enough liquid water.
Third, water has a high energy requirement for melting. It takes 80 little calories to melt a single gram of ice to water without raising its temperature at all. Yet, it only takes one calorie to raise that gram of water one degree from freezing point to one degree Celsius. Thus, it takes 80 times as much energy to melt snow as it takes to warm it one degree. Now, a dog's body temperature is 39 degrees Celsius. So it takes 39 calories to raise one tiny gram of water from melting to body temperature, yet it takes over twice that much just to melt the snow to water without heating it at all! And remember, the dogs already need roughly 10,000 kilocalories per day just to run the race. Mushers can't afford to waste food calories melting snow in a dog's body.
Snow is a very wasteful way to water a dog. A dish of cold water is not much better. Warm soup and fat are far superior.
Every time a dog team enters the checkpoint the veterinarians are surveying the dogs, looking at the brightness of their eyes, the wetness of their gums, the speed that the pink color returns to the gums when pressed, the color of the urine, the stickiness of the skin over the shoulders, and the heart rate--all ways of determining the proper hydration of the dogs.
In addition, the veterinarians question the mushers about the dogs' appetites on the trail, and the dogs are observed as they eat, to insure that whatever water the dogs need ends up inside the dog and not frozen in the pan or spilled on the ground.
The most successful sled dogs carry their water on the INSIDE.
Dr. Jerry Vanek has been a musher or sled dog race veterinarian for the past 30 years, including five Yukon Quests. He is a former officer of the ISDVMA and he continues to write and speak widely on the subject of sled dog medicine.