Domestic cats leave behind a long-lasting chemical calling card in their urine, and scientists from Japan, Germany, and Spain have identified it. The calling card is made up of 13 unusual fatty acids, and this discovery could help explain how felines recognize one another long after a scent mark is left behind.
Professor Masao Miyazaki of Iwate University led the study, whose results appeared in Current Biology. The team discovered that branched-chain fatty acids, or BFAs, produce individual urine profiles that remain relatively stable over time. Cats can recognize these differences, and the research indicates the kidney itself might serve as a storage container for the compounds.
The Scent Puzzle
Felines depend greatly on scent to gather information about other cats, and they regularly collect such data from urine and other odor marks that linger in their environment. These chemical traces can keep communicating for a long time once the animal that left them has gone.
That creates a puzzle: since many odor molecules evaporate, break down, or change with time, how can another animal still determine which animal originally left a scent trail if it is constantly evolving?
Japanese, German, and Spanish researchers have pointed to domestic cats as a possible source of an answer, suggesting that a group of uncommon fatty acids could work as a lasting chemical marker in cat urine.
The 13 Unusual Acids
The researchers singled out 13 branched-chain fatty acids, or BFAs, in their study. Each cat carried its own distinct combination and ratio of these compounds, though the proportions tended to stay roughly the same within the same animal.
Researchers were able to show through behavioral tests that cats can sense differences between BFA profiles, even when the other lipids in the urine are kept the same.
The findings suggest that BFAs could function as a durable chemical “calling card” that helps preserve information about individual identity.
Cats Remember Individual Scents
Before turning to the identification of the chemicals involved, the investigators first had to show that cats could tell urine from different individuals apart.
Cats spent less time investigating the same urine sample after repeated encounters with it. However, when they were presented with urine from a different cat, their interest rebounded, and they devoted more time to sniffing.
Remarkably, cats kept showing weakened responses to previously met urine odors even after months had passed between exposures. That finding points to cats possibly keeping long-term memories of particular urine scents.
Scientists also looked at the flehmen response, that telltale open-mouthed expression cats make when investigating certain smells, and found that cats used it more often when smelling foreign urine than when smelling their own.
Presenting the same urine repeatedly caused the flehmen response to grow less frequent, yet when a fresh urine sample from a different cat was added, the response rose again.
Professor Masao Miyazaki of Iwate University led the research project. He said “After confirming that cats can distinguish individual urine odors, we used the flehmen response as a clue to identify urinary molecules that may contribute to individual scent recognition,”.
The Flehmen Response and Its Clue
The team then put the cats to the test to see if they could actually tell the difference between these BFA patterns. They kept the other lipid parts of the urine samples steady and altered only the donor-derived fraction that contained BFA.
Once cats had gotten used to the original sample, they started sniffing more when the BFA fraction was changed, and that change in behavior gave evidence that cats can tell the difference between individual BFA compositions.
This outcome reinforces the notion that these fatty acids might transmit significant information about individual identity instead of merely serving as unusual chemical byproducts.
The Century-Old Kidney Mystery
Researchers caught a surprise clue involving the kidneys: they found BFAs in that organ but not in any of the other tissues they examined.
Neutral lipids with BFAs were found among those stored inside droplets within the renal cortex. These kidney lipid droplets have confounded scientists for more than a century.
The droplets in question have long been a subject of uncertainty, with their biological purpose remaining unknown despite the fact that cats are known to have large numbers of them. The new research raises the possibility that the droplets function as a reservoir for storing lipids containing BFAs.
A storage vessel like the one being discussed could help keep a cat’s chemical signature relatively steady even when diet or physiological conditions temporarily change. By holding back those short-term fluctuations, the kidney might help maintain a more consistent individual chemical profile in urine.
The Durability of the Signature
Many of the chemicals that give urine its odor are volatile and begin changing quickly after being deposited. The BFA compounds, on the other hand, are semi-volatile and evaporate more slowly, which makes them relatively durable.
When samples were kept at 25°C, the BFA profiles linked to individual cats stayed relatively steady for at least 24 hours. That timeframe implies the signal is strong enough for a cat to come back to a spot and still detect the signature of another cat that had been there.
The Long-Term Memory of Scents
Tests of cat behavior showed that the animals keep long-term memories of particular urine scents. The flehmen response faded as cats grew used to the same sample, but it came back when a new cat’s urine was introduced.
The behavioral evidence points to cats holding on to individual chemical identities across long stretches of time, which fits a pattern of habituation and recognition. The study’s data on behavior backs the idea that BFAs carry meaningful information about identity rather than simply being unusual byproducts.
What We Make of This
It is a charming oddity — a commonplace biological fact that reads like a secret feline code. Cats have marked territory and examined one another for ages, and now we have a chemical explanation for part of that behavior.
The research raises several questions worth watching:
- How do the BFA profiles change over a cat’s lifetime, and do they reflect health or aging?
- Do wild cats carry the same signature, and does it vary across species?
- What triggers the flehmen response in cats, and how do they process the information they detect?
The research provides a definitive response to the long-standing query about those kidney droplets. The new evidence indicates that the lipids containing BFA stored within them serve an entirely new biological function.
Cat owners should take note that the urine their pets leave behind is more than a smell. It carries information about the cat’s identity, and other cats can read it for a while after it’s left.
It is a striking fact to bear in mind that most chemical signs pass swiftly, and yet cats have managed to establish a mark that endures. And now we have discovered what that mark is composed of.
Source material: “Scientists discover a hidden “ID card” in cat urine,” ScienceDaily.
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