Cat is becoming progressively more aggressive to my other cats

[bugmankeith]

I adopted a cat back in July who is 6 years old and a neutered male. This cat had two previous homes before me and spent nearly a year in a shelter, he had many behavioral issues and wasn’t in the best health.
I don’t know about his first home, but his second was in an apartment with no other animals, however his former owner was home maybe 3 hours a day and barely spent time with him. He didn’t eat properly and was very underweight and had little muscle mass, ate plastic bags, paced, howled for hours, pulled his hair out, and got aggressive picking him up and I heard he never had any windows to look out of and the rooms were kept dark. Despite this he loves people and gets seperation anxiety if left alone.
In the shelter he wasn’t adopted because he sat in a corner hiding from the other cats (he was in a cage free enclosure) and he ate so poorly the shelter thought he was very ill.

fast forward to when I adopted him and had him for a while. Almost all his behavioral and health issues stopped. He doesn’t howl or eat bags, all his fur grew back, he gained weight and muscle mass and is VERY active he sleeps maybe two hours a day and plays all day or follows me everywhere. The separation anxiety is the only issue he still has but I don’t blame him after what he went through. He has lots of windows to go in and toys to play in and has the run of the house, we have an enclosed outdoor area so he gets to go outside in the grass and watch the birds.We can pick him up and no aggression. My vet checked him over and found nothing wrong with him, figured it was stress and trauma and loneliness with his past issues.

The problem is with my two elderly male cats who are 15 and 12. They are indoor/outdoor (former ferals who are now tame). They are the sweetest cats and very well behaved, the only thing is they refuse to use a litter box so I let them out to use the bathroom then they come back inside. In warm weather they stay outside all day and night I have a cat house for them that’s sheltered.
When I got my new cat my two males basically lived outside, so my new cat only saw and smelled them on me but never had interaction. Once the cooler weather came they met and my new cat constantly smelt their butts and followed them but after left them alone and they left him alone. They even started eating together and sleeping near one another.
But this month my new cat suddenly started jumping on them biting their neck and spine and trying to get to their belly but no hissing or growling when he does it. My senior cats just try to get away from him but my new cat persists until the cats go out or go into another room. However one bite he did hurt one of my males and he then bit my new cat and made him bleed, my new cat still persisted to go after him right after!

I noticed we have ferals passing by outside and I think after my new cat saw them he thinks my cats are a danger or something triggers him smelling them they probably have the feral scent from using the bathroom outside, he’s never been around intact cats and we have male and females passing by sometimes so maybe this triggers aggression?

I’ve tried separating the cats but none of them will have it and it hadn’t helped the aggression. I have no idea what to do

 

[ArtNJ]

If its true aggression, than yes, smelling an outside cat could have triggered it. However, since there were no noises preceding the attacks, it sounds possible that he now feels comfortable enough in the home and with the two older ones to play with them. You may know this already, but many cats are terrible about ignoring whether the other cat(s) want to play or are protesting/trying to get away. When you say he hurt the other cats with the bites, did they have actual bite wounds? If not, he might just be playing too roughly. Play biting the neck is a super common thing, especially if the second cat just sits there and doesn't engage by assuming the defensive position. And considering the other two cats are older and probably don't voluntarily play at all, its not unexpected that an active 6 year old could be really pushy about play.

Of course, either way its still a problem, but if its overly rough play, the solutions would be different.

 

[FeebysOwner]

Try scent swapping - in this case rub towels/blankets with your 6 yo's scent on them on the other cats when they come in from outside. If they smell like him, he may not be as inclined to bother them - especially since he didn't before. You could also try the 'vanilla' trick as explained here: Ode to vanilla extract

But, you also need to look closely at what, if anything, might have changed in your home, with the cats, etc. around the time this started. There is usually a trigger of some sort. You mentioned the ferals, but I am guessing they have been around all this time - unless there is a new one that has 'joined' the group that might be causing the problem.

Also, an illness in one cat can cause them to become aggressive to other cats, and vice versa - especially if the 6 yo goes after one of the two older cats more regularly than he does the other. So, keep an eye out on all three for signs of a potential health issue brewing.

If can't find a cause and remedy it, you will have to start 'discipling' the offender; take cardboard to separate them if need be, pick up the 6 yo and 'hiss' at him or tell him 'no', say no more, and then give him a time out in another room for a couple of minutes. Repeat using the exact same technique each and every time he attacks one of the other cats, for as long as it takes for him 'to get it'.

 

[rubysmama]

However one bite he did hurt one of my males and he then bit my new cat and made him bleed, my new cat still persisted to go after him right after!

Is the new cat mentioned in the above quote, the 6 year old? Or is there a 4th cat in the mix now?

 

[bugmankeith]

New cat is 6 years old, only 3 cats.

 

[rubysmama]

Things any better since when you first posted?