While the idea of dropping a few pounds may appeal to many of us, unexplained weight loss in pets can be a cause for concern. Cachexia is the term given to unintentional loss of 10% or more of an animal’s body weight in a short span of time.

Unfortunately, such a dramatic weight loss can have an effect on your pet’s entire body, including her respiratory, cardiovascular, and central nervous systems. Some of these effects can be dangerous for your pet’s health, so it is important to get to the cause of her weight loss as quickly as possible. In many cases, treating the cause will enable your pet to put weight back on and return to better health.

What causes weight loss in pets?

There are many different things that can cause your pet to experience unexplained weight loss, some more serious than others. Some of the most common include:

Not eating enough

While many animals have healthy appetites, there may come a point where your pet seems to lack interest in food and may start eating considerably less. If this happens for more than a few days and your pet continues to live a fairly active lifestyle, she may lose weight quite quickly. Similarly, if you are an inexperienced pet parent and aren’t confident in the amounts you should be feeding your animal, you may find that you aren’t giving her quite enough to sustain her weight.

Parasite infestation

Internal parasites are easy to prevent, but they are still a very common problem affecting many pets. Living inside your pet’s body and depleting her of essential nutrients, the greater the infestation, the greater the effect will be on the health of your animal. There are many side effects to living with a parasite infestation, including weight loss.


Diabetes is becoming increasingly common, due to the growing obesity problem among pets in the United States. There are a range of complications associated with diabetes, including weight loss. This is because the body is unable to effectively use the food it takes in as energy. Therefore, your pet may be eating more but still losing weight.

Dental pain/problems

Your pet relies on her teeth to bite and chew her food. However, if she is in pain or discomfort due to problems with her teeth or gums, this may affect both her appetite and her ability to eat. Periodontal disease (infection of the gum tissue) is evident in most cats and dogs by the time they reach their third birthday and can only be prevented with a robust oral hygiene routine and regular visits to your vet.

Cancer in pets

Understandably, the term cancer is a frightening one to hear as a pet owner. Unfortunately, unexplained weight loss is a key characteristic of many types of cancer including gastrointestinal tumors. If your pet starts to lose weight rapidly and has any unusual lumps or bumps, you should seek an appointment with our vet immediately.

Other potential causes of weight loss in pets

  • Poor quality food
  • Inflammatory bowel disease
  • Bowel infection
  • Blockages in the stomach/intestines
  • Pancreatic disease
  • Liver or gall bladder disease
  • Problems with her heart, kidneys or liver
  • Hyperthyroidism
  • Addison’s disease
  • Central nervous system disorder
  • Sudden increase in physical activity
  • Prolonged exposure to the cold
  • Bacterial infections
  • Viral infections
  • Fungal infections


If your pet suddenly experiences unexplained weight loss, we strongly advise that you make an appointment with our knowledgeable and compassionate veterinary team as soon as possible. Our experienced vets can run a range of diagnostic tests to determine the underlying cause of your pet’s weight loss including blood panels, fecal studies, urinalysis and x-rays. Once we establish why your pet is losing weight, we can seek to rectify the problem through immediate treatment.

If your pet is experiencing unexplainable weight loss, please call our office today at 317-434-1900.

Your pets deserve the best veterinary care possible