It's a mistake to think your dog's fur coat will protect him from harsh winter weather.

When the mercury hits freezing, indoor dogs should be taken out for five or 10 minutes only, says Dr. Richard Thoma, a veterinarian in Cheektowaga, N.Y. Don't force your pet to stay out longer than he wants to."If your dog whimpers or heads toward the house, you know it's time to go back in," he advises in the current issue of American Health.

On warmer days, in the upper 30s, healthy adult dogs can be walked for 20 minutes or so. But puppies and older dogs can't stay out as long, says Thoma, because their internal thermal regulators don't work as well.

Doggie sweaters help small dogs and indoor pets retain body heat, allowing them to brave the cold longer. "Even a large, short-haired dog such as a Great Dane will be happier in a sweater. They prevent snow from freezing in clumps between the animal's toes (particularly a problem among long-haired dogs), which can cause frostbite. What's more, paw protectors guard against irritation from chemical ice melters such as rock salt. If your dog doesn't take to paw-wear, just be sure to rinse and dry his feet after an outing.

Here are some other cold-weather tips for dog owners:

- Don't let your dog walk through puddles. Hidden shards of ice or glass can cut the animal's delicate paw pads.

- After a bath, be sure your dog is thoroughly dried before you take him outdoors.

- Don't leave your dog alone in a car on cold days for more than half an hour, and definitely not overnight. Hypothermia, a condition in which body temperature drops below normal, can set in; if it lasts more than two or three hours, the animal may freeze to death.

- A doghouse is a must for outdoor canines. Just make sure the shelter doesn't face north, says Thoma. Put straw on the floor and a heavy blanket over the door to keep in warmth created by the dog's body heat. Thoma even suggests you line the doghouse with building insulation.