VCA Animal Hospitals

Unexplained Weight Loss in Cats and Dogs

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When a pet loses a dramatic amount of weight for no apparent reason, you need to go to your vet as it can be a sign of disease. There may be an underlying condition that needs treatment.


In today’s world in which more than 50 percent of dogs and cats are considered overweight or obese, weight loss is often a desirable outcome for our sedentary, overfed pets. But when pets lose weight despite little effort on their owners’ parts to effect this change, it’s often an unwelcome symptom of disease. This is especially true in cases where weight loss is rapid or pronounced (more than 10 percent of body weight).


Pets can occasionally lose weight for a variety of relatively benign reasons:

  • A change in diet can sometimes cause weight loss either because the pet finds the food less appealing or because it has fewer calories.
  • A move to a new home, a change in schedule, or greater access to the outdoors can lead to weight loss if a pet becomes more active as a result.
  • Geriatric pets can sometimes lose small amounts of weight as part of the normal aging process.

Persistent, rapid, or dramatic weight loss (greater than 10 percent of a pet’s body weight), however, can be the sign of a serious condition, such as:

  • Liver disease in dogs and cats
  • Periodontal disease in dogs and cats
  • Thyroid disease in cats
  • Kidney failure in cats and dogs
  • Cancer
  • Chronic gastrointestinal obstruction (as when foreign bodies are ingested)
  • Diabetes in dogs and cats
  • FeLV or FIV in cats
  • Orthopedic or neuromuscular disease that leads to loss of muscle mass

What To Do at Home

If you notice weight loss in your pet, ask yourself a few simple questions:

  1. Is the pet otherwise feeling well or is she suffering from lethargy, poor appetite, vomiting, diarrhea, or any other obvious symptoms?
  2. Has the pet’s home life or schedule changed?
  3. Has the pet’s diet changed?
  4. Has the pet’s appetite or activity level obviously declined?

If changes in diet or activity level don’t seem sufficient explanation for the degree of weight loss (particularly if the pet’s weight loss is greater than 10 percent of her body weight), a veterinary visit is absolutely in order.

What Your Veterinarian Will Do

There are several steps a veterinarian may undertake to discern the origin of the weight loss.

  1. Get a history. When did you first notice the weight loss? How has it changed? How has your pet been otherwise? How is her appetite?
  2. Do a physical examination. What a pet looks and feels like can tell your veterinarian a lot about weight loss. What do her teeth look like? Does she look otherwise healthy? Checking out the entire pet helps establish what’s going on and is therefore considered an essential step.
  3. Do some basic lab work. A CBC (complete blood count), blood chemistry panel, thyroid hormone test, heartworm test, urinalysis, and fecal examination are considered basic. For cats, FIV (feline AIDS) and FeLV (feline leukemia) tests may also be recommended. For dogs, tick titers (blood tests to help diagnose Lyme disease or other diseases carried by ticks) might be in order.
  4. Take X-rays (radiography). This common imaging study can show if internal organs (like the liver, kidneys, and heart) are enlarged or otherwise abnormal in size or position. Some internal tumors can also be detected by taking X-rays.
  5. Do an ultrasound. Similar to X-rays, this test uses sound waves to help get a more three-dimensional picture of internal organs and to show whether abnormal structures or abnormal organs are present.
  6. Conduct a barium study. This common X-ray study requires that a patient receive a stomach-filling volume of a dense liquid material that shows up as a bright white image on an X-ray. It’s usually undertaken as a series of images, so that the barium’s progress through the gastrointestinal tract can be evaluated. As the barium fills the esophagus, stomach, and intestines, much can be discerned about the structure and function of the GI tract. This test is especially useful when gastrointestinal obstructions or gastrointestinal cancers are suspected.


Definitive treatment depends on the underlying cause of the weight loss.

This article has been reviewed by a Veterinarian.


General Practice

We have over 540 animal hospitals in 41 states that are staffed by more than 2,000 fully qualified, dedicated and compassionate veterinarians, with more than 200 being board-certified specialists. The nationwide VCA family of general practice hospitals give your pet the very best in medical care, providing a full range of general medical and surgical services as well as specialized treatments*: Wellness, Spay/neuter, Advanced diagnostic services (MRI/CT Scan), Internal medicine, Oncology, Ophthalmology, Dermatology, Cardiology, Neurology, Boarding, Grooming

*services may vary by location.

Our family of pet hospitals stands out by delivering the greatest resources in order provide the highest quality care available for your pets. By maintaining the highest standards of pet health care available anywhere, we emphasize prevention as well as healing. We provide continuing education programs to our doctors and staff and promote the open exchange of professional knowledge and expertise. And finally, we have established a consistent program of procedures and techniques, proven to be the most effective in keeping pets healthy.

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Specialty Care

Sometimes sick or injured pets need the care of a veterinary medical specialist. When that happens, VCA specialty hospitals work closely with the general practitioner veterinarians who refer cases to us in order to provide seamless veterinary care to your pet. When your pet is facing any kind of serious illness or injury, our specialty referral hospitals will provide the compassionate and expert care your beloved pet needs.

Our goal is to make sure that when you and your pet are in need that you have access to board certified specialists who are up to date on the very latest developments in their field. In our state of the art hospitals, our specialists also have access to the most sophisticated diagnostic and treatment tools and techniques from ultrasonography and endoscopy to CAT scans and even MRI.

We have twenty-eight specialty hospitals across the US so there may be one near you. Our specialized services include: cardiology, critical care, dentistry, dermatology, internal medicine, neurology, oncology, ophthalmology, radiology and surgery.

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Emergency Care

In case of emergency, please call us immediately. If it is after hours, check with a local animal hospital emergency clinic.