I was posting a thread before here a few days ago, called "Please help, serious concern" about my cats playing behaviour, I thought that everytime my little kitten was playing near the other one, my older cat didn't like it and that's why he screamed at her. But now after watching them closely for a few days, I've noticed that my older cat (3 years old neutered moggy) is constantly yells at her everytime she goes near him, and I've noticed that he attacked her from behind on several occasions and bit her neck, staying on top of her! My poor little kitten doesn't know what's happening, she is shocked because a few weeks ago they were both playing happily together, (she hides from him now and doesn't want to play with him)!! My other cat, Mango is VERY aggressive towards her and everyone in the house, and he is a monster really, I didn't think that a neutered cat can still behave so aggressively, and still have mating behaviour! I am at my witts end here! I tried to seperate them, but Mango screams to let him out. He jumps up trying to open the door and throws himself at the door to let him out he keeps following her and screams at her! It's a total nightmare here! I tried to shout at him, but nothing helps, nothing I can do to stop him behaving like a horrible nasty aggressive cat. He doesn't play, he totally changed, he is not like my little angel Mango at all.

Kia will be spayed in January I hope I don't have to endure this until then!!!! I bought the plug-in Feliway someone suggested to me in my other thread, and I really hope that will take affect soon!!!
Did anyone else experience something similiar? What can I do to calm him down? How long will he behave like this??? Please any advice and sharing experiences with me would be highly appreciated! I just want all of them to be happy together!!! Thank you!

u need to introduce a new cat slowly...
exchanging some poo in the litter boxes, tovels, toys....
cats can easily get jealous and stressed, fixed or unfixed cats does not really matter as you bring a new cat to their core territory, meeting the cat in a park for the first time they surely would not be so aggressive.
Dont worry they will accept eachother just take it easy.
Shouting is wrong! do not do that! Instead you have to give your old cat more attention to make it feel loved and secure!
best would be to keep them separated for the first and let them meet eachother every day on short supervised sessions.
Feed them separately too.

Your cat is scared of the kitten and the kitten is scared even more. once they relax it will be better.
when you let them meet, make sure to have a hand on your cat, rub his cheeks and stroke him always ready to hold him back when he wants to attack the kitten.
If your kitten is hissing and growling back at him you can also stroke the kittens head.

What you can try is:

let the kitten eat and approach the kitten from back holding your older cat in your arms so they don't have eye contact, do not let them have the eye contact because that is where the trouble starts.
Have one hand on the kitties head and hold your cats collar with the other head and let him approach your kittens ass
he might start snooping there right away.
if he start licking your kittens ass, that is a good sign

keep the meeting sessions short, and let them not have eye contact. distract them both, make them look at some toy or something.
let your other cat smell your kittens food and let him eat some of it, put some kitten food in his bowl too. and make sure to feed him first.

if you have 2 cats and if one of them is more friendly with the kitten, then let them stay in one room to get to know eachother on short sessions. if your other cat wants to come inside so badly you have to reconsider what is more worse, a cat who is pissed a bit or a chance that they might fight a hurt kitten and an extended introduction time.

instead you might go out and play with your other cat some more.
do not feed his jealousy by shouting or ignoring him.

get a small towel and rub your kittens cheeks with it than your other cats cheeks, again and again, let them smell it.

they will be great friends later, no worries.

when i got my new kitten... same story again.. the first day i had 3 wild lions, 3 days later my kitten hardly can walk because they are busy licking his ass 247.