Dog owners know that a Chihuahua feels the sting of cold more acutely than a Siberian husky. The decision to add a coat depends on a few factors including the length of fur. The temperature at which your dog needs an extra layer can depend on breed, aggravating weather conditions including wind or precipitation, your dog's size and her individual sensitivity to the cold.
The temperature that should really gauge when your dog needs an extra layer is her internal thermometer. A dog's normal body temperature is between 100.5 and 102 degrees Fahrenheit. She can die if ambient conditions cause her temperature to drop below 95 degrees. A jacket should help a dog regulate her body temperature. When gauging your dog's ability to handle the elements, consider outdoor temperature, wind chill, higher humidity and if your dog is outside her natural element. Saint Bernards are built to withstand the elements, but Chihuahuas and greyhounds just aren't built for the cold. And it's not just the length of a dog's fur but the density that matters in sensitivity to chill. As dog jacket materials vary from polar fleece to windbreakers or puffers, you can find just the right weight to suit the weather conditions and your dog's needs.
If your pooch is a baby, is older or is suffering from a condition that can be affected by the weather, such as arthritis or heart disease, you may add an extra layer of warmth. Try a step-in version that acts as a harness and a warm coat, and zips up the back, if you find it difficult to comfortably get an achy dog's legs through armholes. Or try a barn coat, placed on your pup's back and strapped under the belly and chin. Bear in mind that small dogs who are low to the ground -- and any snow -- will want a coat with some belly protection.
Listen to Your Dog
Dogs can't open the coat closet and pick out a down puffer before heading out to do their business, but you may see doggie language that tells you it's time to bundle her up. Shaking and shivering or whimpering at the wind chill are obvious signs that your dog is too cold. You may notice behaviors that change from the more temperate times of year, such as hesitating to go outside or wanting to come inside sooner than usual.
Depending on how low the temperature gets and your dog's tolerance for the chill, consider winter layers in addition to a jacket. A sweater or thermal shirt can add warmth under a coat and can stay on for household wear. A dog scarf can add extra coziness and style around the neck; be sure to get one sized for your dog -- one not so long that she might trip on it. Dog-wear designers make cold-weather hats for pups that include ear holes and drawstrings to secure under the chin. Boots protect sensitive paws from snow and from irritating ice melt that may be spread across sidewalks on your walking route. Be sure to look for lightweight footwear that doesn't drag down your dog.