Why are my brother cats suddenly hissing, growling, and fighting?

A sudden behavioral change could indicate an issue such as pain or underlying illness, so if this happened suddenly or recently, having both cats examined for any signs of ongoing pain or illness is a good first step. if they check out healthy (aside for any known previous conditions), then adding in something such as a pheromone diffuser can help with stress between cats and aggressive behavior. Making sure both cats have access to their own food, water, litter, bedding, etc can also help decrease tension and stress over these items. If one of your cats is going blind or hard of hearing, adding in nightlights and making sure your cat can get around easily may help reduce stress related to these conditions and reduce tension between both cats.

I'm sorry you are facing this frustrating problem. I would recommend that you take the one who is suddenly being "grumpy" to the vet. Sometimes if they are painful or not feeling well, they will become more irritable. You can try temporarily separating them again, or separating them for at least part of the day so that the "victim" has a "safe zone" or some time where he or she feels safe. But the sudden onset of the change in behavior does concern me that something may be going on with the one who is acting more aggressive. Best of luck, thank you for asking Petco Pet Education Center, formerly Petcoach.

It may be due to illness or injury. It can also be redirected (or displaced) aggression. This is when one cat is unable to directly respond to a perceived threat and "vents" on whoever is closest. This is usually an owner or another pet. Never handle or grab your cat if she is displaying aggressive tendencies. This can lead to a serious bite or scratch. Schedule an exam with your vet to rule out medical causes. If they are indoor cats, provide a ' cool down' period by separating them. Keep stray or strange cats away from windows or doors and out of your yard. Control what your cat sees by closing doors or drawing the blinds. Consider using pheromone products to decrease anxiety/stress level in the house. Search www.pet360.com for pheromone products.

If your cats have spent most of their time outdoors and now are spending time inside together then this change in environment could be causing tensions. If they are still outside all the time then it is possible that a new cat has come into the neighborhood and this has disrupted the social structure of the cats, or potentially one of the cats could be feeling unwell and therefore being more defensive, or they could feel they are having to compete for food/shelter. I would be sure both cats have equal access to food and water (they may need their own separate areas to eat/drink so they don't feel threatened) and litter boxes indoors. When indoors I would recommend the use of the Feliway Multicat diffuser https://www.amazon.com/CEVA-Animal-Health-D89410B-MultiCat/dp/B01AVHPFDS/ref=sr_1_4?ie=UTF8&qid=1503838561&sr=8-4&keywords=feliway+multicat, which is a pheremone product. I would consider an examination by your vet to look for underlying health problems as well.

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!

Cats will often do this if they have been separated for a period of time, especially if one cat looks or smells different - your female cat may have strange smells on her from her time outside. Most of the time, this reaction is mild and the cats will get along again after a day or two. If there is any serious fighting or if his aggressive behavior towards her does not seem to be improving, then you may need to separate them and gradually reintroduce them to each other - feel free to ask for additional help on this if needed :)

I hate to hear that. This situation can very very stressful and it's hard to know why this is happening. It's possible Kyo is sick and his odor has changed. It may be worthwhile to have him examined by the veterinarian to make sure everything is ok. It's also possible the cats are seeing or smelling another cats outside and this is causing stress and bullying behavior. Wipe down doorways and windows to eliminate odors. Here are a couple articles to help with cat aggression and stress: https://www.petcoach.co/article/5-tips-to-handle-an-aggressive-cat/ https://www.petcoach.co/article/causes-of-stress-in-cats/ You can help relieve stress by setting aside 30 minutes a day for vigorous play for each aggressive cat, provide climbing opportunities with cat shelves and cats treats, use a pheromone diffuser and provide separate litterbox and feeding stations. Lastly, your veterinarian can provide medications or a special diet called Calm which may help the cats. Best of luck and please feel free to post any additional questions.