Help please

[sethm6]

So I've had three cats for awhile now and they've always gotten allong great. They groom, eat, and sleep together all the time but I recently adopted a new kitten. My existing cats are 2 9-10 month olds and a year and 8 months, and the new kitten is 4 months old. (Female and spayed) When I first brought the kitten home and introduced her to all of my existing cats they were all fine but then all of the sudden the nine month old female (not spayed yet) freaked out and started hissing and growling. Now two days later the female kitten hisses when ever she sees the other 9 month old male (not nuetered) who is also her brother, and if she even smells the scent of the new kitten she will his and get very agressive. But the oldest cat (females and spayed) is able to get along with both of the other existing cats and they new kitten. I have to keep the kitten and the 9 month old female separated from everyone else now. What should I do to get them all to get along and be in the same room without the 9month old female getting so agressive? I've tried swapping scents and letting them explore each other rooms and while the kitten takes well to this the 9 month old kitten just gets very agressive and stressed out when ever I try to introduce the new kittens scent. All in all I want to know why the 9 month old female is so aggressive towards her brother all of the sudden? And how can I introduce the new kitten to the two month old female without them getting so agressive?

[booktigger]

Your biggest issue is 2 unneutered 9 month olds, being unrelated won't stop mating. It will also make introductions harder.

[sethm6]

I understand it won't stop mating but what I don't understand is why she's so aggressive, I've had cats in heat before and they never where agressive about it.

[booktigger]

There are hierarchy issues between unneutered and neutered females. Do you have plans to get the siblings neutered?

[sethm6]

I do and I understand that she has issues with the new kitten but what I'm confused about is why she is so aggressive towards her brother all of the sudden.

[Lilith]

Hi and welcome

Whew, you nearly didn't need to invite another kitten into the house - you could have ended up with homemade ones - luckily it sounds as if your boy's a bit backward in that department - but don't bank on it!

I used to breed Siamese and had a kitten who I was keeping as brood queen - but she refused to look at a stud. I got her neutered, but not before I found out that an unspayed female can be a right bolshy little troublemaker and bully. They're liable to pick on anyone. I imagine frustration from not being mated comes into it as well. Things settled down after she was 'done'.

So I think that's the first problem to be sorted. You may have further hard work on your hands while hormones (and the situation) simmer down, but you'll get there; the kitten is young enough to adapt, hopefully, and it's good that the kitten gets on well with the older cat.

All the very best with them