Feline Non-Recognition Aggression: Duration, Causes, & Why Your Cat Hisses at Cats After a Vet Visit

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two cats laying together

As a veterinarian, I've seen many strange things, but nothing quite prepared me for the day my own cat turned on her best friend. I've had many clients complain about the perplexing issue of feline non-recognition aggression, but for many years, I had not dealt with it personally. This complex topic falls into the category of "Practical Lessons I Wish I Would Have Learned in Vet School", right up there with "Dental Extractions 101" and absolutely anything on the business side of running a veterinary hospital. 

Imagine a loving multi-cat household. Cats A and B are best friends and do everything together. Cat A goes to the vet and Cat B stays home. Cat A returns to receive anything but a warm welcome from Cat B, who hisses, attacks, and seems determined to destroy Cat A. Cat B is convinced Cat A is an enemy and a threat. A previously wonderful cat friendship seems a distant memory and the household is a tense environment for all humans and pets involved.  

What happened? How long does feline non-aggression last? Is this why my cat is hissing at the other cat after the vet? This strange behavior, known as feline non-recognition aggression, can turn a peaceful home into a war zone. But fear not, cat lovers! Let's delve deeper and explore how long feline non-recognition aggression typically lasts, and what you can do to keep the peace. 

What is Feline Non-Recognition Aggression? 

Non-recognition aggression in cats is a bizarre phenomenon that occurs when one cat is uncharacteristically aggressive toward a companion cat after a period of separation. Cats primarily recognize each other through scent rather than visual cues. When a cat returns from the vet's office or another unfamiliar location, they may smell different due to exposure to other animals, medications, or stress-induced anal gland secretions. This change in scent can cause the cat that stayed home to perceive their companion as a stranger and a potential threat. 

My Personal Experience with Feline Non-Recognition Aggression 

I learned this lesson from the University of Hard Knocks. We travel with our pets, like many people nowadays. Usually this works out well, but our calico cat, Mackenzie, became ill on a recent trip and we soon found ourselves in the vet emergency room at 1am. While Mackenzie suffered no long-term ill effects from the cup of espresso she managed to lap up while I was in the other room, the vacation condo was anything but relaxing when I returned home with Mackenzie the next morning. 

Mackenzie was certainly bright-eyed and bushy-tailed, but it was not from her recent caffeine jolt. Rigby, our Siamese, greeted us at the door with anything but a warm welcome. There was hissing, fur flying, growling, and screaming. Initially, Mackenzie and I were frozen and shocked.

As soon as I could compose myself, I realized that Rigby was experiencing feline non-recognition aggression. She didn't know that Mackenzie was her best pal, as Mackenzie smelled like a complete stranger. 

How Long Does Feline Non-Recognition Aggression Last? 

Unfortunately, there is no easy fix for feline non-recognition aggression. The duration of the aggression can vary from a few hours to several weeks, depending on the individual cats involved. In our case with Mackenzie and Rigby, the aggression lasted an agonizing two weeks. 

Steps to Manage Feline Non-Recognition Aggression 

  1. Separate the cats for as long as it takes for the aggression to end. Gradually reintroduce the cats using a tall pet gate or a "safe zone" where they can see and smell each other without physical contact. 

  2. Bathe both cats to neutralize unfamiliar scents. 

  3. Counter condition the aggressor cat by offering food only when the other cat is in sight, even if they are on opposite sides of the room. 

  4. Engage in scent swapping by rubbing a towel or blanket on the aggressor and then using that to rub down the other cat to transfer the scent. 

  5. When you think things are beginning to improve, take very small steps. Rushing the reintroduction process can be counterproductive, so patience is key. 

The chances that the cats' relationship, or at least tolerance of each other, can be reinstated are good, but future meltdowns are likely once this sensitivity has been recognized. In other words, history is likely to repeat itself if steps are not taken to prevent recurrence. 

Preventing Feline Non-Recognition Aggression 

Preventing feline non-recognition aggression is far easier than dealing with the consequences of an aggressive encounter between your cats. By taking proactive steps to minimize the chances of this distressing behavior occurring, you can help maintain a harmonious multi-cat household. While it may not always be possible to completely avoid situations that could trigger non-recognition aggression, being mindful of your cats' sensitivities, reading their body language, and  taking appropriate precautions can go a long way in keeping the peace. Useful measures to take include: 

  1. Make sure that a cat coming from the vet's office is fully recovered from sedation or anesthesia before returning home. 

  2. Bathe the returning cat to remove veterinary-type odors before reintroducing them to the household. 

  3. After bathing, rub something with the cat's regular scent back on them, such as a blanket or toy. 

  4. Keep cats separate for a while after one returns from the vet's office until they re-familiarize with each other's sounds and odors. 

The Importance of Pet Insurance 

Dealing with feline non-recognition aggression is challenging enough; the last thing you need to worry about is how you're going to pay for whatever medical issues brought you to the vet in the first place. As a veterinarian, I highly recommend investing in comprehensive cat insurance. These policies can help cover the costs associated with unexpected veterinary visits, including those related to behavioral issues like non-recognition aggression. Having a financial safety net in place can give you peace of mind and allow you to focus on helping your cats rebuild their relationship during these stressful times. 

With patience, understanding, and the right techniques, you can help your feline friends rekindle their bond. Remember, even the most complex situations can be navigated with a little love and a lot of positive reinforcement. 

As for me, I think both girls will be traveling to the vet together in the future. That experience was not one I ever want to repeat, and I'm sure both cats would agree.