cats fighting after being groomed

Question
We had my oldest cat (4 years old) groomed for the first time. The groomer told us that he and our other cats may hiss at each other for a couple days. Unfortunately, we're only on about a day and it's it's gone beyond hissing.Two of the cats (the one that was groomed and our second oldest) are fighting. We haven't been able to leave them in the same room - there is hissing, fighting, running after each other to attack. It's been pretty intense! How long will this go on for? Initially the cat who was not groomed started it, but now they both seem very very mad! Help!

Answer
Hi Kim,

Hooboy, sounds like a can of worms has been opened. You have a case of non recognition aggression going on. When the one cat was groomed his odors changed. When he came back his house mate saw him but didn't smell him. It confused the guy who was home. He is thinking a strange cat in the house and time to defend his territory. You need to use a cat introduction protocol and reintroduce them. Also you can get some Feliway Comfort Zone. It might help. It mimics a cat's happy pheromones and relaxes them.

http://www.sdhumane.org/site/DocServer/BT_Cat-Cat_Intros.pdf?docID=621

http://www.sdhumane.org/site/DocServer/Introducing_a_Cat_to_a_New_Territory.pdf?...

These are two good articles that can help. The next time one has to go anyplace like the vets bring the other. This will prevent another episode of this. Good luck and take care.

Ciao, Karen