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Feature June 2018 Issue

Non-Recognition Aggression in Cats

This behavior is not uncommon after a vet visit or other excursion made outside the home. Here's why it happens and how to minimize its effects.

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Spending time getting your kitten or adult cat desensitized to the carrier can be helpful in making excursions away from home less stressful.

Like many cats in a multi-cat household, Ivan and Natasha live together bound by a mutually agreed-upon peace treaty. Indeed, there’s an occasional breach when one crosses the other’s claim to a toy or cherished napping spot — but that doesn’t terminate treaty relations. However, there is one major treaty violation that makes it clear that this isn’t a non-aggression pact: the veterinary visit. It doesn’t matter if they go to the vet together or separately. Once back home, there are no consoling purrs. Natasha lights into Ivan with a barrage of aggressive behaviors as if she doesn’t recognize her peace partner.

This type of intercat aggression between household cats is known as feline non-recognition aggression, and it can occur when a resident cat leaves the house for a period of time to visit the groomer, boarding facility or veterinarian’s office. Additionally, it isn’t uncommon for one or more cats to act aggressively toward the returning cat.

“The issue of non-recognition aggression is not well understood, unfortunately,” says Stephanie Borns-Weil, DVM, head of the Animal Behavior Clinic at Tufts. “Some behaviorists consider it to be a form of territorial aggression that reasserts itself when a cat leaves and then returns. Others consider it better explained as redirected aggression.”

Feline scent communication

To us, the returning cat is the same cat. But the home cat utilizes the olfactory sense to interpret a foreign invader in the territory. Cats communicate using body language — visual, vocal and, perhaps most importantly, scent cues. Each cat has a signature scent that is distributed when cats sleep together, groom each other or casually rub against one another, creating a communal scent of their home territory.

The returning cat’s recognized smell is overlaid with a menagerie of smells from the veterinary clinic environment, which may include other pets, people, medications, treatments and cleaning products. The returning cat may release fear pheromones or, if the cat is taken to the vet because of an illness, may smell sick. These smells smack the home cat right in the nose and are registered as a threat — or perhaps as a reminder of a fearful experience.

The home cat cannot respond to the direct threat or fearful experience so he redirects the aggression toward the nearest substitute, which is the returning cat, theorizes Dr. Borns-Weil. “Alternatively, the cat that had been away may redirect his or her fear experienced during the absence on the housemate. Now it’s game-on for both cats. Non-recognition aggression can be dangerous for the cats, and it can even be redirected to humans.”

Warning signs

“The home cat may display offensive aggression characterized by flattened ears, a hard stare, growling and/or an attack,” says Dr. Borns-Weil. We may think of the returning cat as the defensive cat, but she cautions, “The home cat, if motivated by fear, may also show defensive, aggressive body language characterized by a ‘Halloween cat’ posture, hissing, swatting and/or attacking.” Some subtle signs to watch for include narrow, constricted pupils in the attacking cat; dilated, wide-open pupils in the defensive cat; and raised hair along the shoulders and tail is a common sign in both the attacking and defensive cat.

According to Dr. Borns-Weil, the aggression can last for a short duration or even persist long term. “It varies between cats because much depends on the response of the returning cat. The longer the aggression continues, the more challenging it is to treat,” she says. “Never let the cats fight it out; fighting doesn’t resolve the underlying issue and it doesn’t end well for either cat.”

She recommends treating non-recognition aggression with separation as soon as possible, and then making a gradual reintroduction. Once home, the cats should be separated for a period of time ranging from a few hours or several days. This allows the returning cat to calmly settle back into the home environment and regain the missing mojo after the stress of the ordeal before reuniting with the housemate.

This cat may also need quiet time to recover from anesthesia or recoup from illness. Be sure to set up the space with a set of resources including food, water, litter box and bedding. “The reintroduction should be gradual, from across a large room while providing cats with food, for example,” says Dr. Borns-Weil.

Pre-visit pointers

The old adage ‘prevention is the best medicine’ may apply to non-recognition aggression: It’s circular and it starts at home before you ever leave, according to Dr. Borns-Weil. “The best preparation is to make sure that the cat’s vet visit is as low stress as possible. If the cat who is leaving feels calm and confident, the experience will therefore be less disturbing. As a result, it may be less likely to trigger aggression upon return.

“To do this, I recommend that all cats be desensitized to their carriers and car rides long before they need to go to the veterinarian. These are life skills that should be taught to all kittens. However, for cats that are adopted as adults, the skills can still be learned. Also, minimally stressful handling should be used by the vet and technical staff. Excessive restraint should be avoided. If needed, sedation should be used to facilitate a low stress visit.”

For pet owners with mixed households of both cats and dogs, non-recognition aggression is mostly non-existent. Dr. Borns-Weil, explains, “Dogs do not demonstrate reintroduction aggression, so there is no real concern that the resident dog will show aggression to the returning cat. It is possible — though not likely — that a cat will show aggression toward a dog that is returning from the vet, but territoriality is generally something that is displayed to other cats, not individuals of different species.

“Of course, there are exceptions. If the cat was fearful of the dog before leaving the house or before the dog was taken out, he or she will be fearful when the dog returns and could, as such, display fear motivated aggression.” — Ramona Marek, Ms, ED

Comments (8)

This is a very timely article for me. My two barn cats are sisters who were raised together and for the last year have been inseparable. However, suddenly, last week one of them became very aggressive towards the other, who screams and runs. Neither of them has been away at all.
I'm keeping one of them in a large crate at night in the same room as the other one and hoping for the best, but they are still not allowed to be out together.
Will something like Felaway help? I feel bad, because they were so close before and I can't figure out what happened to trigger this.

Posted by: Tripleransom | November 4, 2019 12:35 PM    Report this comment

When you take a cat to a "new place" be it the vet or elsewhere and return to your home with cat, it has a different odor to it than when it left your house. none of the current cats, except if you have one so laid back nothing fazes it, will immediately accept your returning cat, because they detect a different odor !! This is just the way the cat is - they have much more sensitive noses than people realize and use scent recognition among their peers. Dogs arent the only ones with sensitive noses !
Cats are just smarter ! LOL

Posted by: skyeyes | November 4, 2019 12:04 PM    Report this comment

I'm going to try all natural coconut oil instead of vanilla extract , stay tuned!

I Hypothesize better results than vanilla extract

Posted by: Olivers26 | January 16, 2019 2:54 AM    Report this comment

Had this problem after one of my cats spent several days in the vet hospital. The trick I used worked well. Place a little bit of vanilla on each of their heads. They were back to being buddies within 24 hours.

Posted by: Poohbear64 | October 11, 2018 12:34 PM    Report this comment

We have two cats that are brothers. Unfortunately, due to a respiratory infection, one of them had to spend the night at our local veterinary hospital. When he returned home, his brother hissed and wanted to fight with him. It took a few days for them to get back to normal.

Posted by: Hortonwho | July 11, 2018 3:39 PM    Report this comment

I like all the suggestions here; I'm sure they work basically. My favorite' way of getting two separate cats to blend' is to give each cat a couple of sprays of catnip spray - I use only Bliss Mist catnip spray, which my kitties have indicated is acceptable . . .when they smell alike, there is less aggression . . .

Posted by: Maya's Mom | June 4, 2018 3:07 PM    Report this comment

This has always happened with our cats if one of them goes to the vet and the rest stay at home. It never has taken too long for them to get over it, though.

Posted by: koshka | June 4, 2018 1:00 PM    Report this comment

Great article. I learned this many years ago. I currently have four cats. I bring all 4 of them to the vet for their annual wellness visits at the same time. I always felt that this way they will all smell like the Vet's office and they can commiserate together in the car coming and going! A chorus of singing cats. It's worked very well. For the occasional time that only one has to go, only one of my other cats has had an issue when she returns. Though I've never tried it, someone also suggested putting cologne on the nose of the cat who remains at home. Then, she can't smell anyone. Not sure that would work.

Posted by: Stephanie4Cats | June 4, 2018 12:30 PM    Report this comment

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