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Causes of Weight Loss in Cats

Updated: March 8, 2021 by Kristen Chapple

There are a huge number of different things that can cause weight loss in cats and it can often take some investigative work to find out exactly what is going on. There is no question that weight loss in cats of any age or breed is a significant finding. Except in specific cases, such as when an owner has been trying to intentionally make their cat lose weight by feeding less calories or increasing their exercise, weight loss is a sign that there is something going on.

Some owners may notice that their cat (particularly if they are outdoor cats that like to hunt) can sometimes lose a small amount of weight in the summer and gain it back in the winter. As long as the weight loss is not substantial and the animal still has a normal body condition score, this may be acceptable. Vets will typically have records which can tell them what cats have weighed in previous years and as long as there is a regular pattern, this slight weight loss may be their ‘normal’. It is likely due to the fact that they are more sedentary in winter and spend much more time indoors, lazing about. As a general rule of thumb, a weight loss of 10% or more is a concern.

When we are trying to determine the cause of weight loss, it’s important to look for any other clues that may help us determine what is going on. Owners should pay close attention to their cat; its eating habits, its litter tray habits and its general activity. They should make a record of any vomiting or coughing and let the vet know about them. If a cat normally does its ‘business’ outside, it may be worthwhile bringing them in for a few days to ensure they are urinating as normal and do not have diarrhoea or constipation. Similarly, owners should watch their cat eating: are they leaving hard biscuits behind or having trouble swallowing?

kittens looking at cat food

Owners are encouraged to take a closer look at their cat’s diet and routine. Have they changed food brand or has another member of the family started feeding the cat? Did an over-friendly neighbour who used to spoil the kitty with food recently move away? Did they forget to buy in those yummy treats last month? It can be a good idea to record a cat’s calorie intake over a few days to ensure they are receiving an adequate amount of food. Any treats or human food that they eat should be included. Their calorie requirement will depend on factors such as their age, size and breed and is something that a vet can help determine.

One of the more obvious causes of weight loss in cats, particularly in young adults and active hunters, would be parasites. Cats with worms (such as tapeworm and roundworm) may continue to eat well but will lose weight as the worms are consuming all of the nutrition from the food. Owners may also notice that the cat has a bloated belly, poor coat quality and raised third eyelids. While it is possible to see worms in a cat’s poo or on the fur around their bum, this is not always the case. The general recommendation is that all cats should be de-wormed every 3-6 months with a good quality product. Those that hunt or eat raw food may need to be treated more regularly than this.

Having a heavy external parasite burden, such as lots of lice or fleas, can also lead to weight loss as, not only do they transmit worm infections, they can also lead to excessive scratching and over-grooming which burns a lot of calories. It’s important to rule out these itchy critters by using effective, all-round parasite control.

Another frequent cause for weight loss is oral disease. In a younger cat, they may be experiencing gingivitis while older cats are prone to oral abscesses and rotten teeth. Cats are not generally big fans of having someone look in their mouth, but if an owner manages to, they may notice red gums, a build-up of brown calculus and a foul smell. There is a misconception that cats will stop eating when they have a sore tooth but this is just not the case. In the wild, if a cat were to stop eating they would not be brought to the vet, they would simply die. As cats continue to eat, many owners will overlook the dental disease, assuming all is okay. Clued-in owners, however, may notice that a cat either eats slowly or quickly bolts their food (to prevent any pain when chewing). They may also favour wet food to dry food and may be eating less than they normally would. Veterinarians can swiftly diagnose if there is an issue with the mouth and often a dental cleaning is all that is needed to solve the problem.

When a vet is presented with a cat that is losing weight, they will always perform a thorough physical exam. This examination can help determine where the issue is. They will look for tell-tale signs of an underlying condition such as pale gums, a goitre (thyroid swelling), rapid heartbeat, enlarged or shrunken organs, thickened intestines or a fever. Using their experience, they may be able to make a good guess at what the issue is but will typically run some basic blood and urine tests to accurately diagnose the issue.

cat at the vet on a check up

Many (though not all) causes of weight loss in a cat can be picked up on straight-forward, in-house tests that are relatively inexpensive. Lots of clinics will be able to provide same-day results. Chronic conditions such as kidney disease, diabetes, liver failure, viral infections (such as FIV or FELV) and hyperthyroidism are easily detected from just a few mls of blood.

If a cat is losing weight and their blood and urine tests come back normal, this does not rule out an underlying problem and just means we need to dig deeper. Some causes of weight loss, including Inflammatory Bowel Disease or Intestinal Lymphoma, may not be picked up from urine and blood work. For animals whose disease is not diagnosed from basic testing, they will require some more investigative work. Many will have further, more specific blood work done, which can assess organs such as the pancreas and determine how well the gut is absorbing nutrients. A faecal test may also be ordered to rule out any strange or rare parasites or infections within the gut. Similarly, imaging studies such as thoracic radiographs and abdominal scans are often recommended to search for things such as cancers.

Frustratingly, some conditions are hard to distinguish and it can sometimes be difficult to tell from an abdominal scan if a cat has Inflammatory Bowel Disease or an Intestinal Cancer. Due to this, it may be suggested that biopsies are taken from the gut so that a diagnosis may be reached and a treatment can be started.

It’s important to mention that a rapid weight loss, especially in overweight cats, can lead to a dangerous condition called ‘fatty liver’, or hepatic lipidosis. If untreated, this fat infiltration in the liver can cause liver failure and even death. Owners may notice that their kitty has suddenly developed a yellow tinge to their skin and eyes (jaundice), is vomiting, drooling and hiding away. When offered food, they are unlikely to take it. Thankfully, cats that are treated promptly and effectively have an excellent prognosis and tend to go on to make full recoveries. Time is of the essence and the sooner the cat is admitted to the hospital, the sooner they can recover. Treatment consists of supportive care, nutritional support, intravenous fluids and management of the underlying condition that has led to the lack of eating and weight loss in the first place.

While a vet may initially treat your cat symptomatically, perhaps given them some appetite stimulants, fluid therapy and a high calorie diet, the important thing is to find out why a cat is losing weight so that appropriate course of action can begin. Not every diagnosis will be something that can be cured, and some cats may require lifelong therapy. Many cats will require frequent check-ups and weight checks going forward to ensure that their condition is being well managed.

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