My cats are fighting after one returned injured. How do I stop it?

There does seem to be an unusual phenomenon that when one animal attends the vet for a time its companion can react badly on its return. Possibly due to unfamiliar smells. Usually it settles after a week or so. If not you could try bathing the cat or invest in a pheromone diffuser to try and settle them.

If Gizzy is going out into the garden, then she could come back in smelling differently and that's causing Fergie to be upset. I can give you a method to help them get along again. I would separate the cats, and slowly reintroduce them to each other. Take Fergie, 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 Gizzy in Fergie'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 Gizzy 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 Fergie out of her room, and see how she interacts with Gizzy. 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 Fergie in her room when you go out until they are comfortable with each other.

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!

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

You could start by feeding them on each side of the door that separates them so they can smell each other and have it be a positive experience. Next, you can switch rooms - lock your cat in her room so your cat can investigate the smell of her cat and let her cat roam the house. Then you can try them together while you can supervise and see what happens. You could get some Feliway spray or a diffuser and use that to alleviate any stress/anxiety.

Have the stray examined and treated by your veterinarian. Once he has recovered from his wounds, have him vaccinated and dewormed. Keep them separated during this time. Allow them to hear and smell one another through a closed door. Once they have acclimated to the sounds and smell of a new cat, allow them to see each other at a distance for ever increasing periods of time. Progress to placing the new cat in a closed carrier in the room with your cat until she acclimates. The use of pheromone products, such as Feliway spray or plug in diffuser, may decrease any anxiety or aggression.

I would separate them, and slowly reintroduce them to each other. Take the cat who is aggressive, and put him in his own room with his own food, water, and litter box. For a few days, feed them both treats under the door so they associate each other with a good thing. Then let your female into the room while your male is in a carrier. Praise them when they interact without aggression, and take the female out of the male acts aggressive. Once they get along that way, you can let the make out of his room to see how things go. I hope this helps!