Any canine disease that causes vomiting, appetite loss or diarrhea can also cause weight loss. The relationship between these three things and weight loss is obvious: the fewer calories being retained within the dog’s system, the more likely the dog will lose weight. However, it is also possible for other, more serious, diseases to also cause weight loss in dogs. Due to the seriousness of these diseases, it is important to consult a veterinarian as soon as possible any time a dog experiences unexplained weight loss.
Hypoadrenocorticism, more commonly referred to as canine Addison’s disease, is an uncommon disease that occurs when the adrenal glands produce insufficient quantities of corticosteroids and mineralcorticoids. One potential cause of this disease is an autoimmune response in the dog’s body, causing its immune system to attack its own adrenal glands. It may also be caused by other illnesses or the effects of toxins. Addison’s disease most often affects young to middle-aged female dogs. Dogs of some breeds, including standard poodles, Rottweilers and Portuguese water dogs, may have a genetic predisposition to Addison’s disease. In addition to weight loss, Addison’s symptoms include muscle weakness, unexplained collapse and lethargy.
Canine Copper Hepatotoxicosis (Copper Storage Disease)
Canine copper hepatotoxicosis, or CCH, occurs when copper builds up in a dog’s liver due to specific proteins in the liver or abnormal secretion of copper in the bile produced by the liver. As many as 66 percent of all Bedlington terriers living in the United States have a predisposition to an inherited metabolic defect, which causes the liver to retain copper instead of permitting it to be eliminated. Doberman pinschers experience greater copper toxicity than other breeds because of a lower disease threshold -- they need to retain less copper than other breeds to experience the same symptoms. In addition to weight loss, the dog will show symptoms including anemia, jaundice and the presence of hemoglobin in the urine, or hemoglobinuria. Other breeds affected by CCH include the Skye terrier and the West Highland white terrier.
Cancer and Tumors
Middle-aged and older dogs frequently develop lymphoma, a common form of canine cancer. Dogs with suppressed immune systems may also be prone to developing lymphoma. This kind of cancer has a variety of symptoms; weight loss is commonly seen. Lymphoma is often treated successfully with chemotherapy. Adenocarcinoma of the gastrointestinal system -- tumors in the stomach, intestine or rectum -- of the dog may also cause weight loss accompanied by vomiting blood and black-colored stool. Although Belgian shepherds may have a genetic predisposition to adenocarcinomas, no single breed is more commonly affected than others. This kind of cancer is more often found in male dogs 6 years of age or older than it is found in younger or female dogs.
Dogs with diabetes mellitus either have a shortage of insulin or a resistance to insulin, both of which reduce the dog’s ability to convert glucose to energy. Instead of being utilized by the body, the glucose is excreted in the dog’s urine. This inability to convert glucose causes the dog to experience excessive thirst and weight loss, even if the dog retains a normal appetite and continues to eat normally. As diabetes grows progressively worse, the dog may experience an enlarged liver or impaired liver function that results in ketoacidosis, the body breaking down fat to fuel the body instead of using glucose. Eventually, dogs with diabetes mellitus may become obese. Obese dogs are at risk for diabetes mellitus, no matter their age. Female dogs are also more prone to being affected by diabetes mellitus. Diabetes mellitus may have a genetic component, as it appears to run in families. In addition, various breeds, including miniature pinschers, poodles, dachshunds and beagles, may be genetically predisposed to diabetes mellitus.