Researchers from Japan, Germany, and Spain have identified 13 unusual branched-chain fatty acids in the urine of domestic cats. While the combination and ratio of these acids varied between individual animals, they remained relatively stable within the same cat over time. Scientists suggest that this set of compounds may serve as a long-term chemical “calling card” for the animal.
The study was led by Professor Masao Miyazaki of Iwate University, and the findings are set to be published in the journal Current Biology. According to ScienceDaily, the team first tested whether cats could distinguish between the urine odors of different individuals.
When the same urine sample was presented repeatedly, the animals gradually lost interest in it. However, when the sample was replaced with one from a different cat, the time spent sniffing increased again. A similar pattern was observed with the Flehmen response—a characteristic behavior involving the opening of the mouth to investigate odors; this response occurred more frequently when encountering unfamiliar urine and diminished with repeated exposure to the same sample. Even after intervals of several months, the cats showed a weaker reaction to previously encountered odors, indicating a long-term memory for individual scent signatures.
Next, the scientists analyzed the lipid fraction of the urine and isolated 13 branched-chain fatty acids. When the other lipids in the samples were left unchanged but the fraction containing these specific acids was swapped, the cats began sniffing the sample more actively again. This demonstrated that the animals could detect differences in the composition of these compounds. The profiles differed markedly between individual cats, remained consistent across samples collected on different days, and stayed relatively stable for at least 24 hours in urine-soaked samples stored at 25 degrees Celsius. Heredity likely plays a role: related cats exhibited more similar acid compositions, though individual differences persisted. These compounds are semi-volatile and evaporate more slowly than many other components of urine odor, which tend to change rapidly after excretion. “After confirming that cats can distinguish between individual urine odors, we used the Flehmen response as a guide to identify molecules that might be involved in recognizing individual scent,” said Masao Miyazaki.
The researchers also detected these acids in the kidneys, but not in other tissues examined. Lipids containing branched-chain fatty acids were found in neutral fat droplets within the renal cortex—droplets that are particularly abundant in cats and have remained a scientific mystery for over a century. The scientists hypothesized that these droplets might serve as a lipid reserve, helping to maintain a stable urine chemical profile despite short-term fluctuations in diet or physiological state. “Lipid droplets in cat kidneys have been known for over a century, yet the reason for their abundance remained a mystery. Our findings suggest that one of their functions may be to maintain a stable chemical signature in the urine. A key question for future research is how the fatty acids stored in these renal lipids are ultimately released into the urine,” Miyazaki noted.
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