My Resident cat is very upset about the new cat!! Please help!!

[vada50]

Ok so I bring a new cat I put him in a big safe room. He is being there like a month. I put his fur in my other cats cat tree and feed them between a door so now they are eating next to each other but without seeing each other. So then I decide they could see each other but between a glass dooor. I let the NC explore the house and the resident cat was in the garden wher he could see the NC. From the beginning my RC saw the NC and then my NC cat saw her so he get close to the glass door in a very friendly disposition. But she when crazy with flat ear tail swiping and ran away hissing, growling etc. He didn't care and he didn't even hiss at her. He was still interested and want to be near her (well near the glass) at that moment someone ring the bell and is was people who were bringing my new cat tree, yay, so I went there. When I came back someone open a window and my resident cat enter the house, the horror!!!!!! I found my RC, unharmed under the couch in my room and my NC next to the couch still in a very friendly manner just wanting to smell her but she was growling, flat ear and ready to attack she also try to scratch him, I don't understand why he didn't get it and back away. So I was very afraid my cats get hurt so I make a sound and make my NC cat go away. He went away sad and just walking. And keep exploring the house. I close my room and my new cat was in my bed again in normal behaviour. What I can do now, I have being doing everything right till now I think or maybe is too early. The vet told me to put my NC in his carrier and let my RC smell him and get used to him and then do that to my RC. What do you think. My vet thinks is a good idea to let the cats resolve their issues since first day which I think is a horrible idea!!

 

[moorspede]

I've heard of the method your vet suggested you use and the owner of my second cat insisted that my cats should be introduced to each other straight away. It's great when it works but it's taking an incredible risk. 

Once they are comfortable eating on either side of the door the idea is to open the door a crack or use a baby gate to have them eat with each other between on opposite sides.

Site swapping is to allow the new cat to be comfortable in the space before they are introduced. You usually place the resident cat in the other cat's room so they can both get used to each other's scents.

If it took them a month to become comfortable eating without seeing each other it's likely they will be slower getting used to each other after they see each other.

Your new cat is doing the right things, it didn't back down when the resident cat tried to attack and it didn't become aggressive.

I would go back to feeding them on each side of the door and when they become comfortable with that open the door a crack making sure there is no way either can get through and let them get used to that. Then try limited supervised visits where you are playing with both with an interactive toy, some treats and some verbal encouragement. 

These articles have some great tips:

How To Successfully Introduce  Cats: The Ultimate Guide

Introducing  Cats  to Cats

 

[di and bob]

You are doing every thing right, it just takes a LONG time for a resident cat to accept another. The carrier idea is a good one, jut so it doesn't scare the contained cat too much. I got and installed a screen door to my wood frame (the holes fill in easily with colored wood putty) so the could interact more. To me, she is acting just like all my female cats do, they hiss, yowl, and crouch any time one of my males tries to get near her. It would have been worse, I think, to have another female, she may have attacked then, trying to defend her 'domain'. To me it sounds pretty normal, you might try letting them out together, letting your female hide, and drawing the male away from her to let her relax. As long as there is no out right attacking, you should be OK. All the luck!

 

[vada50]

Thank you for your advice! Yesterday night I try the feed thing again but my female cat was worried and it couldn't be fed next to the door like before I had to back her plate and she didn't eat even though she want too . My NC was normal and eat normally and when the food was gone he went relaxing some other place. I will keep trying. Also my new cat hate the carrier because he knows is a vet visit, he just cries inside but maybe if the female cat came near, he will calm down because he seems to like her. My female cat is spayed, just in case.

 

[moorspede]

The feeding between the door method has you feeding the cats a comfortable distance from the door and gradually moving the bowls closer to each other. 

To stop a cat being afraid of the carrier you take it out for a couple of days and let it become furniture, you can play with them around it and place treats inside. 

I would assume you choose one or the other method. 

The third method is what Di and Bob is suggesting. He/ she believes that what you thought was an attack was actually your female cat being territorial. Using this method you would supervise them closely and allow them to work it out between them. The worst possible thing would be for them get into a yowling, fur flying, blood letting brawl. 

If at any time you see one cat looks like it is about to pounce, or if things are getting a little too intense. Clap your hands or tell them "No" in an authoritative voice. to distract them from it. You then take a toy and play with them or you could even separate them for a few minutes for things to settle down.