Microbes Make the Messages in Cat Poop

Bacteria in the anal glands of a cat are responsible for chemical signalling via poop, study shows.

Bacteria in a cat's anal glands are responsible for chemical signalling via poop
A Bengal cat. Photo: Shvaygert Ekaterina/Shutterstock

By Zazie Todd, PhD

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Many species of carnivore use chemical signals in faeces as a way of communicating. Stinky secretions from the anal sacs, on each side of the anus, provide odours in poop that are used for chemical signals and scent marking.

Wolves and spotted hyenas use these to mark territory; it is believed domestic cats do too, although this behaviour is not fully understood. Striped hyenas, spotted hyenas, and ferrets use these chemical signals to recognize other individuals. Skunks and honey badgers even use these secretions as a form of defence, and if you’ve ever met a dog that’s been skunked, you know how bad that is. Now new research from UC Davis, published in PLOS One, sheds light on how the smells in these secretions are made in cats.

The anal sac secretions from domestic cats convey information about the sex of the cat and its reproductive state, and can also be used to recognize specific cats. For some time, scientists have hypothesized that the odours in these secretions may not be made by the cat, but could come instead from bacteria within the anal sac. This is known as the fermentation hypothesis, and has already been shown for striped and spotted hyenas.

So scientists set out to test this in cats. “Cats use a lot of volatile chemicals for signaling, and they probably don’t make them all,” said David Coil, one of the authors of the paper.

The scientists analyzed secretions from the anal glands of a male Bengal cat. Bengal cats are a cross between the domestic cat (Felis catus) and the leopard cat (P. benegalensis). The cat’s anal glands were manually expressed by a veterinarian as part of the cat’s regular veterinary care, and the owner gave permission for the secretions to be studied.

The scientists extracted the DNA from the secretions and sent it to Dalhousie University to be sequenced. They cultured the most common bacteria from the swabs. And they tested both the secretions and the cultured bacteria for any volatile chemicals that they gave off.

The results showed there were not really that many bacteria in the secretions from the anal sac, and certain types predominated. In fact, only six genera were responsible for 98% of the bacteria. These are mainly anaerobic groups of bacteria that have also been found in other places, including inside the human gut.

A total of 127 volatile organic compounds were found in the secretions from the anal sacs. When the scientists looked at the volatile compounds from the bacteria, they found 67 different compounds, of which 52 were also found in the secretions from the anal sacs.

This is in line with the hypothesis that the chemical signals in the poop are produced by bacteria in the anal sac. Also in line with this, previous research shows the chemical pathways by which many of these bacteria produce volatile compounds.

This is a fascinating result and raises many questions, such as whether cats have any control over this. (See more on the importance of chemical signalling in cats).

Previous research has shown that domestic cats can tell the difference between poop from familiar and unfamiliar cats, as shown by the length of time spent sniffing. The new research raises the question of how different cats have different smells. If it is to do with bacteria, as seems to be the case, how do they get them, and do they change throughout the cat’s life? More research with more kitties is needed.

One thing’s for sure: this shows the important role microbes play for cats.

Speaking about the earlier research on hyenas, Dr. David Hughes, who was not connected to either study, told Live Science, “We often look at hyenas as one organism. But it's not an organism, it's a collection of genes that belong to the hyenas and the microbes. And that's true for hyenas, humans, aphids — wherever we look, it's a collection of organisms."

And that’s the case for cats too. You’ll never look at your own cat the same way again.

If you liked this post, check out my book Purr: The Science of Making Your Cat Happy. Modern Cat magazine calls it "a must-have guide to improving your cat's life."

Yamaguchi, M. S., Ganz, H. H., Cho, A. W., Zaw, T. H., Jospin, G., McCartney, M. M., Davis,  C.E., Eisen, J.A. & Coil, D. A. (2019). Bacteria isolated from bengal cat (Felis catus× Prionailurus bengalensis) anal sac secretions produce volatile compounds associated with animal signaling. PLOD One 

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