Changed Behavior, Your Cat Suddenly Attacks Another Cat or You...
A word of caution before I begin - ** NEVER GET BETWEEN FIGHTING CATS!!! **
This is for your protection. Do what you can to separate them, and confine each separately, but never get between them bodily to break them up.
When your cat who has always been docile, friendly and even snuggly with other cats suddenly becomes a terror to one or more cats - or even you - there is a problem. There can be any number of reasons why a cat will suddenly become an angry cat.
Sometimes, this is easy to figure out, like a vet visit or bad behavior, or even a grooming incident. But in other cases, this is very difficult to figure out, with no definite cause that we can pinpoint. In these incidences, the situation can only be calmed at best, and it will be an uneasy truce.
In all cases, the use of peppermint extract is the first line, so be sure you have some on hand. Putting some peppermint extract on cotton balls and scattering them around is much less expensive than the pheromone treatments and much more effective. You can even rub some extract on the cats to calm them further.
Let's discuss the various reasons why a cat may turn on his buddy...
Vet Visits - The first and foremost reason a cat will be attacked, is that it has been to the vet and has that "vet office" smell on him. This can be easily fixed by an application of peppermint to all the cats or baths all around, to make everyone smell the same.
New Cat - This is most likely when there is a new cat added to an already multiple cat household, and that cat is acting out or being "pegged" into a position in the pecking order. Occasionally, the new cat will attack the older, more established cat. Generally, this is the established cat attacking the newcomer in pecking order determination.
If the new cat is attacking the established cat, and continues to do this, your established cat will likely think it is getting replaced and give up. It can become quite ill and terrorized. You must contain the new cat and support the established cat.
Never allow rough-house play between the cats during the first month. Offer toys and play, but other cats should not be the toy.
Grooming Incidents - This is when you are grooming one cat, and it cries out in pain or is just complaining. The other cat(s) will rush you and try to attack it. Do not allow this. Pick up your patient and leave the room.
This behavior is strange, but I've seen it many times. I usually just tell the others to stop and they are well - behaved but interested in the one being groomed. They know they are next, so they take it easy. However, if you have one cat that needs to be groomed and one that does not, this creates a lop-sided relationship. Having long-hair and a short-hair at the same time is what I'm talking about. Use a slicker or shedding tool on the short-hair to even things out a bit.
Travelers Outside - This is perhaps the most perplexing of them all. Your cats may be indoor only or indoor/outdoor. A stray shows up outside, and all heck breaks loose. You don't know what to do or how to fix it. The dominant female is suddenly beating up the other - usually male - cat.
First, deodorize outdoors. Get rid of the calling cards that the visitor left when he stopped by. You can use the SCOE-10x I recommend for indoors or you can use Skunk Remover.
Next, put up some repellents. These can be mechanical, chemical, or electronic. Whatever you do, make it contain the entire property.
It is likely that a female wandered by in season or a male wandered by looking for same. There will be urine markings all along the bottom foot or so of your building and on some of the plantings. You cats will likely mark in response indoors, so you will need to deodorize there, too.
Many unexplained cases are likely due to this. Apartment dwellers can only treat the indoors, and the peppermint does wonders. Many effective herbal remedies exist, too.
Male Dominance - This is an un-neutered - and sometimes neutered - male response to the female pheromone. If your male is not neutered, please have that done. The aggression towards humans may not yet be apparent, but it will come out. If your male is neutered and still exhibits this behavior, add some Relaxi-Herb to his water or put some on his fur. If you live outside the US, contact me and I'll give you an herbal recipe that is similar to Relaxi-Herb so you can make up the infusion.
Jealousy - If you had one cat can now have two, this will be apparent pretty quickly. The first meeting will not go well. Your established cat is very threatened by the new cat. Confine both and start the introductions over again - after a 3-day cooling off period. Each cat gets to spend time with you during that time. Each cat gets time on the bed - the #1 prime turf in the house! So, confining one in the bedroom is not allowed.
Make sure you provide extra litter boxes for at least the first month.
This jealousy may ease, but each will always view the other as a possible rival. Team play will build the bond. Make sure you use the peppermint and if one needs to see the vet, they both go. The joint experience can bring them closer together.
Pecking Order - This is most likely when a new cat joins the tribe. However, occasionally an older cat is challenged and loses. This will happen as a cat reaches the end of his or her life. I suggest that you remove the cat from the general population - provide a quieter part of the house, such as your office, for the cat's primary daytime residence. The cat will choose where it wants to go. This cat will become depressed, so watch that it eats and drinks. Give it plenty of love and affection.
Inter-level challenges can also happen as an adolescent cat challenges a weaker adult.
You generally have to let things work out. If they become particularly heated, or fur begins to fly, separate the cats and confine them overnight. Larger cages in the same room work well. The cats can see each other but can't get to each other. Lots of vocalization, but that's fine. Make sure they have water and litter boxes in the cages.
General Skirmishes - These are not one cat turning on another, but I wanted to include it here because many people mistake play-fighting for the real thing. If fur is not flying, don't worry about it. It could be a grooming session that turned into "I don't want" or play. This is often an invitation to "Chase me, Chase you" games, and other play. Cats are very playful creatures, and the way they relate to each other is different than the way they relate to us.
Note for All - Please trim the claws on your cat so that if you should somehow get in the middle, you won't be terribly hurt. A stray claw can contain a lot bacteria and cause a serious infection. If the skin is not broken, then this is unlikely. Keep the claws trimmed.
Remember that you have a wild animal in your house. These cats seem quite tame and docile. They may become quite civilized, but they can revert to wild animals in the blink of an eye. The observation and interaction you have with your cats will be a long-term, interesting, and at time heart-wrenching relationship.