Normally dogs take ten to thirty breaths per minute. This varies with temperature, activity, and size of the dog. In hot weather, a normal dog may pant up to 200 times per minute. A dog that is breathing faster than normal may be taking shallow breaths that aren't as efficient at moving oxygen into the lungs. If your dog seems to be working to breathe, not just breathing naturally, something is wrong.
Difficulty in breathing can have a number of causes that may or may not be related to the respiratory tract. A dog in pain often has quick, shallow breathing. Any abdominal problem that puts pressure on the diaphragm can cause respiratory difficulty as well. A dog that has been hit by a car or had other trauma might have broken ribs or what is called a pneumothorax (free air in the chest, putting pressure on the lungs). Pneumothorax is a serious, potentially life-threatening problem that requires immediate veterinary care.
There are many respiratory causes of difficulty in breathing, starting at the nose and working down to the lungs. A dog with a respiratory infection may have purulent (pus-filled) discharge from the nose that blocks his airways. Any obstruction in the nose — blood clots from banging the nose on something hard, inhaled foreign objects, or tumors — can reduce the amount of air going into the lungs.
The same holds true for all the airways down to the lungs. Dogs can also inhale foreign objects into the trachea. Certain dogs, such as many toy and brachycephalic breeds, may have a collapsing trachea, which decreases the open airway of the trachea or windpipe. These dogs may cough, gag, or struggle to breathe deeply.
Pneumonia and Other Lung Problems
Once air gets down to the lungs, other problems can arise. Pneumonia is an infection of the lungs by either viruses or bacteria. It can be quite serious, especially in puppies or dogs with poor immune systems. Dogs with pneumonia may cough, gag, retch, or just have painful breathing. These dogs usually show other signs of illness such as a fever or poor appetite, and they may cough up greenish mucus.
Pneumonia can also be caused by parasite migrations, such as with roundworms, or if the dog aspirates, or inhales, bits of food into the lungs. If your dog has pneumonia, your veterinarian may perform a process known as a tracheal aspirate. This involves injecting sterile fluid into the trachea, then sucking it back out into a syringe so it can be cultured and examined. X rays are also very important in diagnosing pneumonia.
It is common for cancer to spread or metastasize to the lungs. The cancer cells block or overwhelm healthy lung tissue, making it harder for your dog to get enough oxygen. Radiographs or ultrasound examinations of the chest are very important for all canine cancer patients.