Aggression between Family Cats following Surgery

Separate Warring Cats, then Reintroduce Carefully

I have a brother and a sister cat. They used to be very loving to each other by sleeping, playing, and cuddling. Then the male cat swallowed a thread that led to an emergency surgery. Upon his return he was a “new” cat to her. She has since growled at him and wants nothing to do with him. He bullies her too. We have a cat tree and other vertical high spaces, plenty of indoor space for her to stay hidden, plenty of daily interactions with toys and supervised outside visits.

Dr. Nichol:
You are right; when your boy made his grand entrance reeking of anesthesia his sister thought he was from a distant planet. Her fearful signaling triggered his defensive aggression. Their shared trust is toast but your environmental enrichments are a good foundation for these squabbling siblings. It’s time to reduce the animosity and mend the rift.

Each kitty needs a break from his/her nemesis so they can abandon their mutual enmity. They should swap areas of your house daily, never laying eyes on each other for several months. Rub the same cloth on each cat’s cheeks then on the sides of the other’s chest. A small bit of sibling stool left in each litter pan will help them recognize the other’s scent.

With relative peace restored you can begin the slow, repetitive, and tedious process of reintroducing them. Email me at for the general structure. This will take at least a few months; there are no reliable short cuts.

A tasty antianxiety supplement called Zylkene can help. Feliway Multi Cat, available as a plug-in diffuser, is a pheromone that reduces social tension. Medication could be important for a significantly fearful kitty but a custom-tailored behavior modification plan would yield the best results. You are welcome to contact my office for a consultation.
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