Weight loss isn’t a disease in itself rather it is a sign of an underlying problem. Weight loss can be quite subtle as the cat’s coat can make it difficult to see when this is occurring.
Your cat’s weight should be checked at least once a year, during his annual visit to the veterinarian. He will then have a baseline to go on. Unfortunately, many pet owners put weight loss in senior cats down to old age, but it is extremely common for cats to have underlying medical causes. Weight loss may include loss of fluids (usually due to vomiting and/or diarrhea), loss of fat, loss of muscle mass or a combination of all three, it can further be divided into the following:
Impaired intake – poor appetite, inadequate diet.
Malabsorption – An impairment of food absorption such as a lack of digestive enzymes.
Changed nutritional requirements – Organ dysfunction, hyperthyroidism or pregnancy.
The medical term for weight loss due to disease is cachexia.
How much should a cat weigh?
Cats come in all shapes and sizes, so it isn’t possible to give you a guideline on how much a cat should weigh. A small Siamese cat will weigh less than a large Maine Coon or British Shorthair. Not only are the latter cats larger, but they also have a different body type.
Every cat owner should regularly weigh their cat and assess their condition, as well as an annual veterinary examination. Obviously, not all cats will cooperate by standing on a scale, the easiest way to determine their weight is to stand on the scale yourself and note the figure, pick up your cat and stand on the scale a second time and note the figure. The difference is your cat’s weight.
Veterinary attention should always be sought if your cat is losing weight, so he can identify and treat the cause.
The cat above is a seriously underweight due to hyperthyroidism. It is easy to see that she is underweight, note the unkempt coat and the skinny looking hind leg.
I have lost two cats to diseases which caused weight loss (kidney disease and cancer), and both times it happened right before my eyes. Because of their coat, weight loss had been masked. This is obviously very unscientific, but both times I didn’t realise weight loss had occurred until I actually picked up the cats and noticed a huge difference to how they normally would weigh.
Physical signs your cat is underweight
The cat feels very bony. The ribs on an underweight cat will be easy to feel when you run your hands along the sides and the spine can easily be felt when running your hands along the back.
The hind legs appear bony when significant weight loss has occurred.
There is a significant pinching in behind the ribs. This should occur in all cats, but it is much more obvious in cats who are underweight.
There is an obvious loss of muscle mass. Even slender breeds of cat should have good muscle definition, particularly around the shoulders.
Take a look at the chart at the end of the article for further information on determining if your cat is a healthy weight.
There are many possible reasons which may be further split into acute (sudden) or chronic (slow and progressive), other may refer to a condition which may be acute or chronic depending on the underlying cause.
Acute causes of weight loss:
Acute kidney disease – Resulting in decreased function leading to toxins building up in the body.
Infection – Bacterial, protozoal and viral infections can lead to acute weight loss due to anorexia and/or vomiting and diarrhea.
Chronic causes of weight loss:
Chronickidney disease – Disease of the kidneys resulting in decreased function, which causes toxins to build up in the cat’s body.
Addison’s disease – An endocrine disorder caused by the adrenal glands not producing enough hormones.
Diabetes mellitus – A very common endocrine disorder caused by not enough insulin being produced by the pancreas, or insulin resistance, resulting in cells not taking in enough glucose.
Dietary – Insufficient calorie intake (malnutrition) which may be due to poor quality food, inadequate amount of food, fussy eater, dominant cat (or dog) who eats the majority of the food.
Feline infectious anemia (hemobartonellosis) – Caused by an unusual type of bacteria which attach themselves to the wall of red blood cells, destroying them in the process.
Feline leukemia virus – FeLV is a viral infection caused by reovirus, which is in the same family as the feline immunodeficiency virus. It is an oncovirus, meaning it can cause cancer. It also suppresses the immune system.
Gastric ulcer – Open sores develop in the lining of the stomach, due to increased production of stomach acid, certain medications, parasites, stress, Helicobacter pylori and systemic disease
Glomerulonephritis – A renal disease which is caused by the inflammation of the nephrons in the kidneys.
Heartworm – Parasitic worm infection of the heart and lungs.
Parasitic worms – Heavy infestation with hookworm, roundworm or tapeworm can lead to weight loss due to loss of nutrients.
Pregnancyand lactation both use up a lot of the female’s nutritional resources. If adjustments aren’t made to her diet to compensate for this, she will lose weight.
Stress or depression – Some possible causes include moving house, loss of a companion, new pet/person in the house, hospitalisation, being boarded).
This list is by no means complete, there are also many other possible causes of weight loss in cats.
Weight loss can be further split into polyphagic which means progressive decrease in body weight in the presence of an increased appetite. Hyperthyroidism is a common cause of polyphagic weight loss, particularly in cats over eight years of age. Or weight loss which is a result of decreased appetite, increased activity (which leads to more calories being burned), decreased access to food, quality of food, pregnancy, lactation etc.
Other signs related to weight loss may include the following:
Behavioural changes such as depression, withdrawal, sleeping more
Your veterinarian will perform a complete physical examination from you and obtain a medical history, including the cat’s age and other symptoms you may have noticed.
Hyperthyroidism and diabetes are common causes in older cats and may be tested for first. Tests your veterinarian will commonly perform include:
Biochemical profile, complete blood count, and urinalysis to evaluate the overall health of your cat and the organs, these tests may reveal infection, kidney function, liver function, anemia, calcium levels, magnesium levels which can all paint an overall picture of your cat’s health.
Bile acid test – To evaluate liver function.
Abdominal x-ray or ultrasound to evaluate the organs, look for tumours or blockages.
Blood tests to detect elevated levels of the hormones T3 and T4 are performed. Some cats with hyperthyroidism may show normal levels of these hormones in their blood test. If this is the case then a T3 suppression test may be performed. This involves taking a blood test to check the levels of T3 and T4, 7 oral doses of the thyroid hormone T3 and a blood test after the hormone was given. In a normal cat, the level of T4 will drop, in a cat with hyperthyroidism the T4 levels will stay the same or increase slightly.
Fecal studies to look for parasites.
Treatment should be aimed at addressing the underlying cause (if there is one) as well as supportive care and nutritional support which may include appetite stimulants or feeding tube in a cat with anorexia.
Full details on most of these medical conditions can be found in articles relating to the condition (linked above).
Kidney failure – Low protein diet, phosphorous binders, fluids to treat dehydration.
Addison’s disease – Lifelong replacement of missing adrenal hormones.
Hyperthyroidism – Radioactive iodine to destroy the tumour or surgery to remove it.
Hypertrophic cardiomyopathy – There is no cure for this condition, treatment is aimed at relieving symptoms including beta blockers to assist with contraction of the heart muscle, blood thinning drugs and restricting activity.
Diabetes – Switching to a low protein diet, insulin injections may be required if dietary management is unable to bring the condition under control.
Pancreatitis – Find and treat the underlying cause, if possible. Painkillers to relieve discomfort, anti-nausea medication, antibiotics if there is an infection and supportive care.
Exocrine pancreatic deficiency – Pancreatic enzyme extract, feeding a high protein diet. Antibiotics are sometimes prescribed to treat bacterial overgrowth in the small intestine.
Liver disease – Nutritional support, IV fluids, anti-nausea medication, corticosteroids may be useful in some cases.
Inflammatory bowel disease – Dietary management with a highly digestible diet, corticosteroids to reduce inflammation, immunosuppressive drugs, sometimes antibiotics will be prescribed.
Glomerulonephritis – Diuretics to remove fluid excess, low sodium/high protein diet, medications to treat high blood pressure, steroids to reduce inflammation.
Cancer – Treatment will depend on the type of cancer involved and if it has spread. If it is possible, surgical removal of the tumour. Chemotherapy or radiotherapy may also be given.
Infections and parasites
Infections – Antibiotics will be given to cats who have a bacterial infection. Protozoal infections can be difficult to treat with medications although in some cases antibiotics will be administered. Supportive care will also be necessary which may include fluids to treat dehydration as well as nutritional support.
FIV and FeLV – These conditions cannot be treated, supportive care is offered. This may include keeping your cat in a stress-free environment, antibiotics to treat infections that may occur, keeping your pet parasite free, feeding a high-quality diet. Regular checkups with your veterinarian.
Parasitic worms – Hookworms, roundworms, and tapeworms can be easily treated with anti-worming medications. Heartworms are more difficult to treat. Mild cases may require the use of an adulticide to kill the heartworms. This comes with risks and is generally only used in cats displaying symptoms of heartworm disease.
Pregnancy and lactating cats have higher nutritional needs than other adult cats and as such, need to be fed more.
Dietary – Ensure your cat is fed a good quality, well-balanced diet to meet his nutritional needs. Cats should be fed from separate bowls, in separate areas if necessary as some cats can hog the food bowl.
Stress – Finding the cause of stress and reducing it. Avoid changes in routine, spend time playing with your cat, ensure inter-cat conflict is managed, always give all cats a safe place to go on their own with different areas, perches, and beds.
How much should I feed my cat?
According to DVM, the best way to calculate your cat’s daily requirements is to use this simple formula. This calculates your cat’s RER (resting energy requirements) which is the amount of energy (in calories) expended in a day without any activity, it is similar to basal metabolic requirements.
Once you have calculated your cat’s RER, the formula then shows how to calculate your cat’s DER (daily energy requirements) which is a number of calories your cat should eat.
Calculate your cat’s resting energy requirements: 30 x your cat’s body weight in kilos (1 kg = 2.2 lbs) + 70.So, let’s look at some examples below.
Average cat who weighs 5 kg: 30 x 5 kg + 70 = 220 is your cat’s RER
Kitten who weighs 1 kg: 30 x 1 kg + 70 = 100 is your cat’s RER
Obese cat who weighs 6.5 kg: 30 x 6.5 kg + 70 = 265 is your cat’s RER
Underweight cat who weighs 3.5 kg: 30 x 3.5 + 70 = 175 is your cat’s RER
Now you have your RER (resting energy requirements), you need to calculate your cat’s DER (daily energy requirements). To do this, you take your cat’s resting energy requirements and then apply the following formula.
Calculate your cat’s daily energy requirements:
RER x 2.5
Normal desexed adult (maintenance)
RER x 1.2
RER x 1.4
RER x 1
RER x 0.8
RER x 1.8
Now to calculate the DER (daily energy requirements):
A 5 kg cat who is on a maintenance diet and doesn’t need to gain or lose weight. 220 RER x 1.2 = 264 calories per day.
A 1 kg kitten who is growing. 100 RER x 2.5 = 250 calories per day.
A 6.5 kg obese cat who needs to lose weight. 265 RER x .8 = 251 calories per day. Obviously, as your cat loses weight, his RER will drop and you should adjust this formula. The same goes for kittens, a kitten’s weight will gradually increase, and therefore you will need to recalculate his daily energy requirements weekly.
A pregnant and lactating female should be allowed to eat as much food as she likes to stay healthy. Pregnancy and lactation use a huge amount of the female’s resources and she should be fed to accommodate these extra needs.
Feed your cat a good quality, high-calorie diet to help with weight gain and check his weight once a week.