Many people who own small dogs, or who have been around them for any length of time, will have noticed that these dogs often shake. I am not talking about the shaking that a dog does when it is wet and trying to dry itself, but an entire body tremble as if it were shivering.
There are several reasons why small dogs shake and tremble more than most larger dogs.
Small dogs have a harder time keeping warm and as such some do shake simply because they are cold. This helps their blood to circulate to help them to stay warm. Some extremely small dogs (often marketed as teacups) have heart deformities resulting in poor circulation, as such they are even more likely to feel cold than any other small dog.
Many small dogs need to wear sweaters, even indoors, especially if the house is cold.
Some small dogs are not raised correctly, they suffer from a behavioral condition known as small dog syndrome in which they are often fearful. In some cases the owners actually, unintentionally, encourage their small dogs to show fear. If the dog is on a leash, and even shows the slightest sign of fear, some owners pick up and hold their dog, thus rewarding it for being fearful. As such this is sometimes a learned condition.
It is always good to take young dogs to obedience lessons for proper socialization, and for owners to realize that dogs need to be dogs, not fashion accessories. There is no good reason to reward fear in a dog, all it does is create a more fearful dog, but sadly some owners enjoy feeling like they are comforting and protecting their dog, thus encouraging it to be more fearful and needy.
Many small dogs have problems with low blood sugar. This is why many small dog owners, and particularly those with pups, runts, or otherwise stunted “teacup” dogs, need to feed them 4, or more, small meals per day in an effort to keep the blood sugar levels stable. For people whom would find feeding the dog so many times during the day to be too much of an effort, leaving some dry food out all day long is okay, but not the ideal. Canned food should never be left out, as it will rot.
Disease and Infections
Other conditions, such as Addison's disease, illness, or pain, can cause a dog to shake, however these conditions are not specific to small dogs.