My cats fight after vet visit. How to make them friends again?

This happens quite a bit actually. Could be territorial aggression - she left and now he is trying to tell her the house is his OR it could be that he feels threatened due to the way she smells when she returns. I suggest you start using some Feliway products. I would spray the carrier when you take the cats to the vet and use the diffusers (multicat) in the house. ( https://www.feliway.com/us ) ( https://www.feliway.com/us/Why-Use-Feliway/how-to-stop-cats-fighting )

This is very common when a cat escapes or stays at a vet for a very long time, as their scent changes can stress out the other cat in the household. A good first step is to bring Simba to a vet ASAP, especially if he is injured, to treat all injuries and make sure he doesn't have any illnesses that could be passed onto your other cat. Once he is healthy, you can begin to reintroduce them again slowly, either by sniffing each other through a door, or by providing plenty of places for both cats to hide and get away from each other as needed. If a fight does break out, separating the two and trying again later is best. Pheromone diffusers such as Comfort Zone may also help, as well as providing extra food, water, and litter so that they do not compete or fight over shared resources.

Unfortunately, it is very common for one cat to come home from the vet's office only to have the other cats show aggression toward them. It is not from the UTI itself but likely because of the smells he has on him that are foreign to the other cats. Typically this will stop after a couple days. You could get some Feliway Multicat diffusers to help the situation: https://www.petco.com/shop/en/petcostore/product/feliway-30-day-multicat-diffuser-plug-in-starter-kit

Cats exhibit this behavior sometimes when one leaves the house. Most of the time it’s more growling and hissing and running then anything else. Most cats will get over this quickly. Supervise them so that they don’t hurt each other and make sure one does not bully the other. If you have something they really like it such as canned cat food, you could try feeding both cats the food or treats close to each other and talking sweetly and petting both. I hope this helps and best of luck!

Oh dear, how stressful! Unfortunately it can be common for cats to lash out when one cat in the household suddenly smells or acts different - as they tend to do when they come home from the vet. Most of the time they go back to their normal interactions once the strange smell (in this case, from the vet clinic) wears off and the cat relaxes and acts like herself....but in your case, there's nowhere for Tribble to hide and isolate herself while she readjusts to being home. The most important thing right now is to not allow them to fight or have negative interactions. As long as they can be kept separate while they both settle down, they will probably do ok - but if they continue hissing and growing, and worse yet if it escalates into a fight, that could permanently damage their relationship. I would absolutely keep them separate until they seem to be relaxing. I understand that'll be challenging in a 1 BR living space - but if possible, you could put 1 in the bathroom with her own litterbox & food, and then have them switch places tomorrow so they can get reacquainted with each other's smells. If that's not possible, you may need to crate them both while you work on their reintroduction. Perhaps you could borrow dog kennels so they can each have their own living space while they're confined. I know this isn't an easy answer - but the most important immediate intervention is to do what you need to do, to keep them from fighting while the stress levels come down! Finally, adding a pheromone diffuser such as Feliway Multicat may help promote a calming atmosphere. I hope this helps!

Did Pernell go to the vet recently or leave the house for a period of time? When cats go to the vet or leave the house for a period of time (such as going to a kennel), they can come back smelling differently and that would cause the existing cat to view the returning cat as a stranger. Then that would lead to aggression. Or it could be that Gattino isn't feeling well. If he was in pain that would causing him to react aggressively to Pernell. I'd recommend a check up with the vet for Pernell to make sure everything is ok. I hope this helps!

Great question! Washing Rikku and Lucy will have changed their smell, and they now see each other as strangers. I would separate the cats, and slowly reintroduce them to each other. Take Lucy, and put her in her own room with her own food, water, and litter box. Keep the door closed, and for a few days, feed them both treats on other side of door so they associate each other's smell with a good experience. Then let Rikku into Lucy's room while she is in a cat carrier. They can smell each other, but not be in contact. If either becomes upset or show signs of aggression, remove him from the room, and try again later. Praise them when they interact appropriately. When they are interacting well with each other through the carrier, you can let her out of her room, and see how she interacts with him. Praise them when they interact appropriately, and separate them with any sign of aggression or upset. I would get a cat tree with lots of shelves to give the cats vertical space to get away from each other. I would keep Lucy in her room when you go out until they are comfortable with each other. I hope this helps, good luck!