Why Has Older Cat Suddenly Started Attacking Younger Cat?

by Jorgen
(Sweden)

Our two cats, a 5 year old neutered male and a one year old neutered male got along fine in the beginning, but lately the older one is hissing and attacking the young one every day.


The young one has clearly shown that his older roommate is the boss but the old one pounds away anyway. What can be reasons for this cat behaviour?


Reply from Liz (Editor): It's sometimes difficult to figure out the reason for this type of cat behavior, but there will be a reason behind it, and if you can discover what it is, you have the best chance of solving it.

Has your young cat recently been to the vet? Sometimes the smell of the vet's surgery on one cat scares the other cat and can cause an aggressive reaction.

Is there any chance either cat could be ill? Illness can sometimes make cats behave very out of character, including sudden aggression. It works both ways - in other words a sick cat may be aggressive towards a well cat or vice-versa. If you suspect either one could be ill, I'd take them to the vet to rule this out as a cause.

Has anything else changed that could have upset the older cat? Sometimes when this happens, one cat will take out his frustration or annoyance on the other cat - even if the other cat isn't the direct cause. An example of this could be if another male cat is hanging round outside. Your older cat can smell this cat, doesn't like it, but attacks the younger cat because he can't attack the real cause of his frustration.

Changes in the environment - e.g. visitors, house move, loud noises, any sort of upheaval etc. can also cause this sort of cat behavior. If there's anything you can think of that could be upsetting the older cat, see if you can eliminate or reduce it. A Feliway diffuser can sometimes help to calm cats down in these situations.

In the meantime, if you can, make sure your younger cat has somewhere he can escape to when your older cat shows this aggressive behavior.

Best of luck with solving this and thank you for your question.

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