Researchers at the University of Vienna have uncovered a surprising metabolic characteristic in domestic felines. The isotopic signature of their fur resembles that of organisms subsisting on plant matter, despite the fact they remain obligate carnivores. This study’s findings were published in the journal Frontiers in Ecology and Evolution (FEE).
Meat consumption is an absolute necessity for cats. However, stable isotope analysis of nitrogen found in their whiskers and fur indicates that their isotopic data aligns closely with figures typical of human vegans. This finding casts doubt on the established methods for determining an animal’s diet based on tissue isotopes.
Nitrogen isotopes are conventionally employed to assess an organism’s position within the food web: a higher proportion of $^ {15}\text{N}$ corresponds to a greater “trophic level.” Typically, animal tissues exhibit an enrichment of $^ {15}\text{N}$ relative to their diet by 3–5‰ (parts per thousand), a phenomenon known as the trophic discrimination factor. Yet, in cats, this factor was unexpectedly low, settling around just 1.6‰.
The team analyzed the fur of 35 indoor domestic cats fed commercial diets, alongside the whiskers of 14 other animals. For comparative benchmarking, hair samples from 653 humans with diverse dietary patterns—ranging from omnivorous to strictly vegan—were utilized. The cats’ $\delta^{15}\text{N}$ values registered approximately 6.5–6.6‰, closely matching the figures observed in people who adhere to a plant-based diet.
The authors posit that the cause lies in the efficiency of the feline metabolic system. Commercial diets contain high-quality protein whose amino acid profile closely mirrors that of the cats’ own tissues. This allows amino acids to integrate into the keratin of the fur almost directly, causing virtually no alteration to the isotopic composition. Humans and other animals process proteins less efficiently, which consequently spurs a greater isotopic “shift.”
Naturally, the authors stress, this does not imply that cats follow a vegan regimen. Rather, the low $\delta^{15}\text{N}$ values merely reflect subtle nuances in their metabolism. Future plans for the scientists involve investigating whether this effect manifests in other tissues, such as blood, muscle, and bone.
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