If you cohabit with a feline flatmate like I do, you'll observe them spending a lot of time grooming.
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This is normal behaviour for cats, whose barbed tongue makes a particularly effective hairbrush.
Instead of removing their fur from the "brush" afterwards, it is swallowed, to be passed through the gastrointestinal tract and expelled, uneventfully, as faeces.
If a cat has a condition that prevents grooming - such as a sore mouth due to severe dental disease - it is amazing how quickly their coat will deteriorate, forming knots and dreadlocks, accumulating dandruff and scurf, and looking generally rough and dirty.
With the exception of breeds like the hairless Sphynx or guard-hair lacking Rex breeds, most cats shed copious amounts of fur.
Which means their ordinary fur-clearance mechanism can become overwhelmed, leading to masses of fur accumulating in the stomach and small intestines.
When this occurs, the result is known as a fur ball. Fur balls, or trichobezoars as they are referred to in the scientific literature, are distinctive, solid masses that form in the gastrointestinal tract (usually stomach or small intestine) of cats and other species that groom or consume a lot of hair.
"Tricho" refers to hair, while "bezoar" describes a solid mass composed of indigestible material.
As an aside, it is notable that not all "bezoars" are made of fur: phytobezoars are masses composed of vegetable or plant material, pharmacobezoars are masses composed of medications, and lactobezoars are masses of congealed milk and mucus, occasionally found in the stomachs of human infants.
But when they form, trichobezoars are usually expelled by vomiting.
The solid fur ball is usually easily identified in the vomitus for those who can bear to look closely. Occasionally they are misidentified as a small rodent.
Sometimes fur balls cannot be eliminated in this way.
They may become lodged in situ, causing an intestinal blockage. Alternatively, they can become lodged as cats try to expel them, leading to obstruction of the oesophagus or even the back of the nasal passages.
These obstructions may need to relieved either via endoscopy (a flexible endoscope is used to grab the fur ball in an anaesthetised cat) or surgically.
Fur ball obstructions may just be the result of bad luck, or they may occur due to an underlying intestinal disorder.
Because fur balls are associated with vomiting, many owners dismiss vomiting in cats as simply a case of regular fur balls, and don't seek veterinary attention.
Regular vomiting - which may or may not be accompanied by fur balls - can be a sign of serious illness and should be checked by your vet.
The occurrence of fur balls can be minimised by helping your cat remove as much excess fur as possible through regular brushing, if your cat tolerates it.
Alternatively, cats can have a lion clip under sedation or anaesthesia. This removes the bulk of their fur, though it does grow back eventually.
Commercial anti-fur ball diets are available, but these tend to be higher in fat and are not suitable for all cats, so check with your veterinarian first.
Paraffin-based laxatives given orally may help fur balls move along the gastrointestinal tract, so they can emerge in faeces, a lot nicer than being expelled during a potentially projectile, and usually inconveniently aimed, vomiting episode.
My long-haired cat Hero allows me to groom him using a combination of the Furminator and a fine-toothed plastic comb, although he maintains certain no-go zones (particularly his belly). He happily takes a paraffin-based laxative if it is administered in combination with a seafood flavoured treat.
We still experience the odd fur ball - usually delivered on a rug or important paperwork at 3am, but their frequency is much reduced.
Dr Anne Quain BVSc (Hons), MANZCVS (Animal Welfare), Dip ECAWBM (AWSEL) is a lecturer at the Sydney School of Veterinary Science and a practising veterinarian.