Abnormal Weight Loss in Dogs

By Courtney Barnes, BSc, DVM; Krista Williams, BSc, DVM; Ernest Ward, DVM

My dog is losing weight and I don't understand why?

Weight loss in dogs can be associated with many normal and abnormal conditions. This article refers to weight loss that is unintentional. If your dog is on a diet and you are concerned that they may be losing too much weight, please consult your veterinarian.

Weight loss is clinically significant when it exceeds 10% of the normal body weight and when it is not associated with fluid loss or dehydration. For example, a healthy golden retriever that weighs 70 pounds, typical for the breed, would have to lose more than 7 pounds before the weight loss would be considered clinically significant. Changes in diet (not including restricted-calorie foods), environment, or stress levels, including the addition of new pets, may lead to weight loss that is rarely permanent or significant. The more rapid the weight loss, the more potentially concerning it is.

What has caused my dog to lose weight?

Dogs lose weight when they take in fewer calories than their body requires. This imbalance may be caused by the following factors:

  • high energy demand associated with excessive physical activity or prolonged exposure to a cold environment
  • a hypermetabolic state, during which the body burns calories at a faster rate due to an underlying illness
  • inadequate or poor-quality diet
  • insufficient food intake due to lack of appetite (anorexia), swallowing disorders, or regurgitation
  • malabsorption and/or maldigestion disorders (a decreased ability to digest and/or absorb nutrients from food)
  • excessive loss of nutrients or fluid from vomiting, diarrhea, or excessive urination

What other signs should I look for?

Weight loss can be caused by disorders in many of the body's organ systems, and conversely can affect all organ systems. Questions that may provide insight into the cause of your dog's weight loss include:

  • Is your dog's appetite normal, increased, or decreased?
  • What kind and how much dog food are you feeding your dog?
  • How and where do you store your dog food?
  • Has there been changes in your dog’s activity level?
  • Does your dog have any trouble swallowing?
  • Have you observed any regurgitation or vomiting?
  • Has your dog been drinking and urinating more or less than normal?
  • What color and consistency are your dog's stools?
  • Is there a change in volume or frequency of stools?
  • Has your dog been spayed or neutered?
  • Does your dog have a fever or seem excessively tired?
  • Is your dog on regular heartworm prevention?
  • Is your dog tested and/or treated regularly for intestinal parasites?
  • Is your dog on any other medications or supplements?

How can the cause of my dog's weight loss be diagnosed?

Your veterinarian will obtain a thorough medical history and perform a nose to tail physical examination. Additional testing, including blood and urine laboratory tests, X-rays (radiographs), and possibly an abdominal ultrasound may also be recommended.

What are some of the common diseases that cause weight loss?

Many diseases can cause weight loss. In fact, most chronic diseases will result in weight loss at some point during the disease. However, some of the more common conditions associated with weight loss include the following:

  • Anorexia (lack of appetite) due to a behavioral condition or disease. Causes are widespread and can include cancer, infectious diseases, and diseases of the major organs (heart, liver, kidneys, gastrointestinal tract, central nervous system).
  • Decreased nutritional intake caused by loss of smell, inability to grasp or chew food, swallowing disorders, or regurgitation.
  • Prolonged vomiting or diarrhea.
  • Malabsorptive disorders that inhibit the body’s ability to absorb nutrients from the intestinal tract, such as infiltrative and inflammatory bowel disease, lymphangiectasia, or severe intestinal parasitism.
  • Maldigestion disorders such as exocrine pancreatic insufficiency, which interfere with the body's ability to break down food into usable nutrients.
  • Diseases that affect metabolism such as diabetes mellitus, hypoadrenocorticism (Addison's disease), hyperthyroidism (rare in dogs), and cancer.
  • Neuromuscular disease resulting in weakness or paralysis.
  • Increased caloric demand associated with excessive physical activity, prolonged exposure to cold, pregnancy or lactation, and fever.

What can be done to treat my dog's weight loss?

Treatment will be determined by the specific cause of your dog's weight loss. Once your veterinarian makes a specific diagnosis, they will initiate treatment to resolve the problem or improve your dog's quality of life. This may involve diet changes, medications, and other treatments geared toward your dog’s specific problems.

What is the prognosis for my dog's weight loss?

The prognosis ranges from good to poor, as it really depends on your dog's specific diagnosis. A thorough medical history, complete physical examination and appropriate diagnostic testing will assist your veterinarian in determining both the prognosis and the best course of treatment for your pet.

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