Why is my cat being so aggressive?

[Freddieandchip]

I have 5 cats. One of them is 15 years old and he has suddenly become extremely aggressive towards my other cats. He has never liked them too much but they always coexisted totally fine and left each other alone. Sometimes they would have small fights but it would be over in 10 seconds and there was usually a cause (usually them trying to play with him when he doesn’t want to). Now, he will just attack them out of nowhere and when they run he follows them. This morning he attacked all of them so aggressively that I had to separate them. He will attack them while they’re laying down quietly. I have him in my moms bedroom alone right now. Nothing in his environment has changed, he was just at the vet 2 weeks ago and everything is totally fine with his physical exam and his blood work. This happens pretty gradually and is actually the reason why I took him to the vet but it has just gotten worse since then. I plan on calling my vet when they open but I just thought I’d post here incase anyone has any ideas while I wait.

 

[ArtNJ]

Cats often have sensory changes as they get old. Maybe he cant recognize their smell anymore. Thats all it takes for many cats.

I'm sure there are a lot of other possibilities too, although many of them are things that either you or the vet would likely have noticed other signs off like arthritis, visiion changes, dementia.

 

[rubysmama]

Consulting with your vet again is probably a good idea, to ensure there's not something new going on, but it could just be something pertaining to his age. Here's an excerpt from the TCS article: What To Expect As Your Cat Ages – TheCatSite Articles

Increased Aggression (Grouchiness)​

Has your happy-go-lucky adult cat become a grumpy old man? Well, you’d feel a bit touchy too if you found yourself feeling stiff, sore, or weak, or discovered that your senses aren’t what they used to be.​

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Cats suffering from cognitive decline may also become a bit more aggressive due to the disorientation and confusion that they’re experiencing as part of their advancing age. If your cat is settled into one spot comfortably, try not to bother or move them unless it’s absolutely necessary. Your cat needs extra love and patience as they settle into their twilight years.​