10. Weight loss
When a dog suddenly looses weight there are often two common causes, the first and more common cause is a parasite or more specifically some sort of tapeworm in the stomach or intestines. The second most common cause of weight loss is cancer though. The cancer cells eat use the glucose from the food eaten by the dog as an energy source allowing the cancer to grow. This in turn will malnourish the dog, because the dog won’t receive proper nutrition even if it’s eating a properly balanced diet.