Why Does My Cat Poop Smell Bad? Our Vet Shares What to Do

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  • Cat stool is known for its unpleasant odor. If that odor changes (almost always for the worse), you need to consider why.

    What is a normal cat stool like?

    Normal cat feces does have a particularly strong odour. Researchers found that cat feces contains a malodorous material known as MMB with the chemical structure 3-mercapto-3-methyl-1-butanol. This derivative of feline, a sulphur-containing amino acid present in cat urine is thought to play a role in marking.

    There will be an odour to the stool, but it should not be so overpowering, that you can smell it in the next room.

    Keeping an eye on your cat’s stools is important as they can sometimes reveal an underlying health condition.

    • Cats usually defecate (pass a stool) between one to two times a day
    • The stool should be well-formed, and soft, not watery or in dry and/or in pellets
    • The normal colour for a stool is chocolate brown

    Is it serious if my cat’s poop suddenly starts to smell bad?

    First, check if the stool really smells bad, or is your cat defecating outside the litterbox or not covering her stool in the litterbox. In both cases, the odor may seem much worse to you but is actually normal. Generally, a true worse odor is associated with actual changes in the poop. Let’s now look at causes of smelly poop.

    When to call the veterinarian

    If the especially malodorous fecal material has obvious blood in it (which can change the odor), you need to contact your vet. The same is true if the stool is darker than usual which could indicate digested blood from higher up in the gastrointestinal tract.

    Diarrhea, especially if combined with vomiting, is a cause for concern. Loose stools often have an unusual odor. Diarrhea that persists for more than a day or so, especially if your cat is also vomiting, means you need to contact your vet.

    Most common causes of smelly poop / smelly feces

    1. Litter tray issues

    Most cats are hardwired to bury their feces to avoid alerting predators to their presence. If you have a cat who is not burying his or her feces, there may be an issue with the litter tray. Possible causes include dirty litter trays, inter-cat bullying, the type of cat litter or litter tray and the location. Cats feel vulnerable when they are defecating, and if a cat is being harassed by another cat, he or she may deposit their feces, and then scoot from the area.

    Dirty litter trays can be offputting to cats. Solids should be removed at least twice a day, wet areas daily, and trays emptied, cleaned and refilled with fresh litter once a week. There should be one tray per cat, plus one extra. Instead of lining them up next to each other, place them in different locations.

    2. Low-quality food

    All commercial dry cat food contains some form of carbohydrate fillers which are necessary for the pellets to hold their shape. Cheap brands of cat food can contain higher levels of low-quality fillers to produce cost-effective food.

    Fillers (such as corn and other grain fillers) are not a part of the cat’s natural diet and are poorly digested, which can often lead to GI upset, along with flatulence and smelly feces. Corn is

    It is also worth noting that cheap products don’t necessarily save money because they are lower in nutritional value than premium brands; the cat needs to consume more to meet its dietary needs.

    By law, cat food packaging must label its ingredients in order of the highest level to the lowest level, so always look for brands which list meat/s (such as chicken, beef, lamb) in first, and preferably second and third too.

    Some cats do just fine on cheap cat food; in my experience, cheap brands did cause their feces to take on a much stronger smell. They have since been switched to a mid-range brand (along with raw chicken wings), and there is a noticeable improvement in their feces. All pet foods (even cheap brands) which have the words ‘complete and balanced‘ on their packaging must meet AAFCO standards.

    3. Bacterial infection

    Salmonella and Escherichia coli are bacteria that can live in the gastrointestinal tract of cats, causing inflammation and strong-smelling feces. The most common route of infection is via contaminated food or water and hunting (especially birds). Raw feeding exposes your cat to more bacteria but many cats adjust and handle this without problems. A true bacterial infection almost always presents with diarrhea.

    4. A sudden change in diet

    Some cats can be sensitive to changes in diet which can lead to mild stomach upset. Even if you haven’t changed brands, the pet food manufacturer may have changed an ingredient that can cause an upset.

    If you do want to swap the type or brand of food you feed your cat, do so gradually, over several days by adding a small amount of the new food to the current food, increasing the new food while decreasing the old food.

    5. Food intolerance

    Food intolerance is an adverse reaction to food, one of its ingredients or additives. It differs from a food allergy in that there is no immune system involvement. Food allergies typically cause nonseasonal itching, especially around the head and face, swollen and inflamed areas on the face and ears, hair loss due to itching, vomiting, strong-smelling feces, and diarrhea.

    A common food intolerance that many people have heard of is milk. This is because mammals stop the production of lactase, the enzyme necessary to digest lactose, which is the major sugar in milk. Food intolerance is often associated with loose stools and flatulence.

    Other causes of food allergies and intolerances in cats are fish, beef, eggs, wheat, and milk. Cats can become allergic and intolerant to foods they have eaten for a long period.

    6. Maldigestion and malabsorption

    Maldigestion and malabsorption are several disorders in which the small intestine can’t absorb enough of single or multiple nutrients. There are many steps involved in the process of digestion, and any defect can cause malabsorption.

    With any of these causes, you might notice loose stools and a difference in the color of your cat’s poop. People will often comment on how their cat’s stools are « oily » or very shiny. Color may range from yellow to orange. Weight loss is often associated with these problems.

    What should you do?

    • Any changes to your cat’s stool, including an abnormally strong odor should be evaluated by a veterinarian if it does not return to normal within 24-48 hours.
    • Bring along a stool sample which may provide a pointer as to the underlying cause.
    • In the meantime, switch the cat to a bland diet of boiled chicken and rice. This will help to rest the gastrointestinal tract and can help relieve the issue of smelly feces.
    • Any changes at home need to be done gradually. That includes changing litter type, moving a litter box to a new location, and any dietary adjustments. Depending on what signs your cat shows and her fecal analysis shows, your vet will give you things to try.

    Tip for multi-cat homes: It can be hard to identify whose feces belongs to which cat in multi-cat homes. If you suspect one cat is producing smelly feces, feed each cat separately and shave a small amount of non-toxic Crayola shavings to the food. Each cat has his or her unique color, make a note so you don’t forget. The shavings will safely pass out of the cat via the feces, which can help to identify the cat with the smelly stool.

    If your cats resist eating their “color coding” you can isolate each cat into a separate room with their own litterbox.


    The veterinarian will obtain a medical history from you, which may include:

    • How long have the feces been smelly?
    • What is the consistency of the feces?
    • What do the feces look like? Dry, pale, frothy, greasy, bloody?
    • Have you changed your cat’s diet or given her new treats?
    • What is the cat eating and drinking?
    • Is the cat on any medications or supplements?
    • Do you treat the cat for parasites?
    • Are there any accompanying signs?
    • Do the symptoms come and go?

    Diagnostic workup:

    Baseline tests: Complete blood count, biochemical profile and urinalysis to evaluate the overall health of the cat

    Fecal flotation: A small sample of stool is mixed in a tube with a liquid flotation solution, the solution is strained to remove solids and centrifuged for five minutes. A coverslip is placed over the tube and left for ten minutes. The coverslip is removed and placed liquid side down on a microscope slide and evaluated for worm eggs.

    Fecal smear: A thin smear of feces is examined under a microscope to identify Giardia trophozoites.

    Snap test: IDEXX Laboratories have a SNAP Giardia test kit which is available for in-house testing, the sensitivity of this test is 90%.

    Diagnostic imaging: Radiographs or ultrasound to evaluate the organs, look for cancer.


    This will depend on the underlying cause but may include:

    • Gradually change the cat over to a high-quality diet, start with 75% current diet and 25% new diet for 3 to 5 days. Then move to 50/50 for 3 to 5 days and follow that with 25% current and 75% new for 3 to 5 days. At that point, switch to all new diet.
    • Avoid milk or other food products which may be the cause of food intolerances.
    • Regularly treat your cat for intestinal worms.
    • Address the underlying cause of cats with pancreatitis as well as supportive care including pain relief, anti-nausea medication, fluids as well as nutritional support.
    • Lifelong administration of pancreatic enzyme extract, high protein low fibre diet and vitamin B12 for cats with pancreatic enzyme insufficiency.
    • Dietary modifications, corticosteroids or other drugs to suppress the immune system and in some cases, antibiotics to treat inflammatory bowel disease.
    • Consider adding a probiotic to your cat’s diet – use one designed and approved for cats – not a human one.