Whereas humans identify each other mostly by sight, cats rely on their sense of smell to tell friend from foe. Friendly cats sleep together and rub on each other to create a group scent. When cats approach each other, they might bump noses and sniff to make sure this cat is part of their group.
If cats don’t recognize each other, hostility can occur between cats. Even littermates that have lived together peacefully for several years can start fighting if their friend’s scent is unidentifiable. This often happens after one cat leaves the home, perhaps for a visit to the vet clinic, and returns smelling differently. That uncharacteristic aggression after a separation is called non-recognition aggression.
Why Does Non-Recognition Aggression Occur?
Scent is the primary reason a cat might not be recognizable to their feline housemates when returning home. The smell of the vet clinic may even remind the other cats of scary needle pricks or handling that happened last time they were at the vet. The returning cat may also be acting strangely if he is recovering from anesthesia or is still feeling ill. From the moment you open the carrier door, they know something is different about this cat and may perceive him as a stranger or a threat.
Now from the returning cat’s perspective, he is likely stressed from his vet visit and maybe not feeling well. He gets home and is surrounded by his curious housemates, sniffing him intently and acting oddly. In this mood, he might be more likely to tell them to back off.
Non-recognition aggression can take the form of subtle avoidance of each other or full-on brawls. If cats begin fighting, never let them “work it out” on their own. Carefully separate fighting cats with a pillow or heavy blanket and put them in different rooms for at least a few hours to calm down. It may be a good idea to keep the cats separate for a while and slowly reintroduce them over days or weeks.
How to Prevent Non-Recognition Aggression
Preventing aggression from happening in the first place is important because it can be difficult to rebuild their trust in each other after a negative experience like fighting. When you return home from the vet, have a separate room set up for the cat to be alone while they decompress. Give them a few hours there to lose the vet office smell and pick up their home scent again.
If your cat has an extended stay at the vet, perhaps overnight, it can be helpful to provide a blanket with their own scent. Place a towel, blanket, or old t-shirt on their favorite bed or resting spot several days before the appointment so it starts to smell like them. Adding that to their carrier or kennel can provide them comfort and help maintain their home scent. When returning home, you might rub one of these towels against the cat before reintroducing him to the rest of the household to reinforce his normal scent.
Preventing non-recognition aggression requires thinking like a cat – and their nose – to set them up for a happy reunion with their housemates.