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My name is ***** ***** I will be glad to help with your cat problem. My apologies that you did not receive an earlier reply. Various experts are online at different times and I recently logged in and read your question. Your patience is greatly appreciated!
Bless you for caring for so many cats/kittens! You are saving precious feline lives with your kindness and are an angel!
From your description of the situation, there are various possibilities for Oleg's sudden change in behavior. The arrival of the young kittens may have sparked a territorial reaction in him and he hopes to assert his dominance as 'top cat' in the group. Most cats in the household will have a 'leader' and Oleg may want to establish this position. It's also possible that Oleg is feeling very stressed/anxious by the addition of the new kittens and this is causing his aggression.
There is a condition called 'redirected aggression,' which occurs when a cat experiences a startling or frustrating experience and he will take out his feelings on the ones closest to him--his feline companions. Here is more information: CLICK
It would be a good idea to separate Oleg from the other cats for the time being, until he calms down. I would first suggest trying to 'reintroduce' him to the rest of the cats by petting him with a slightly dampened cloth or paper towel and then pet the other cats, then vice versa. Repeat this frequently, so they are all carrying each others' scent on their fur and smelling each other all the time. You can also pet Oleg and the rest, with an old t-shirt of yours, which has a familiar and comforting scent.
In addition, get some Feliway plug in diffusers. These emit calming pheromones which help in stressful situations. Here is more information: Feliway The feliway-type pheromone also comes in a collar, so you might want to try that: Calming Collar
There are other over the counter calming remedies for cats which are given orally; these may help, too. Choose only one to give; do not give both simultaneously:
Rescue Remedy for Pets and Composure treats
Redirected aggression usually takes a little while to subside, but it depends on the particular cat and the situation, so it's difficult to predict how long it will take for Oleg to stop this behavior. Hopefully, it won't be too long.
Once he seems a little calmer, try playing with them with interactive toys, where you direct the play, and reward him and the others with cat-healthy treats so they associate the playing and each other with something pleasurable. Here is a list of different kinds of toys Oleg and the other kitties should enjoy:
There's always a possibility that Oleg is exhibiting this behavior if he doesn't feel well, so an in-person evaluation by the vet, might be a good idea, if the problem doesn't resolve soon.
I would not recommend using a spray bottle, as that usually just agitates the cat and makes him more stressed. However, when you see him preparing to attack or attacking, you can stand out of sight and shake a can or jar of pennies or pebbles so the noise distracts him and stops him. Don't let him see you, because we want him to associate the startling sound with his actions and not with you.
I hope all will be well with Oleg and all your other kitties!
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