When Longtime Feline Friends Turn Enemies


If your formerly peaceable cats have started fighting, and things are looking serious, it’s probably not a situation that can be fixed.

That’s the news from board certified veterinary behaviorist Dr. Debra F. Horwitz at the 2016 NAVC Veterinary Conference in Orlando, Fla.

What causes outbreaks of aggression between housemate cats? “Fights can occur between cats that have lived together for some time perhaps due to a change in social status or a traumatic event, fights may be the sequel to redirected aggressive behavior or another anxiety producing event, aggression may occur with the introduction of another cat, or due to illness or social changes within the home,” she said. “Fear, anxiety, and territorial responses all contribute to intercat aggression within a household.”

First, the bad news: Dr. Horwitz said that severe territorial aggression between cats in a household has a poor prognosis, and even drug therapy is rarely curative. These cats will probably need to live entirely separately at all times and permanently, or one of the cats will need to be rehomed.

In such cases, she said, “Cats may begin to fight when a young resident cat reaches social maturity (between 1 and 2 years of age), when an aging cat leaves the home or changes in their interactions with the other cats, another cat enters the home, or resident cats experience a shift is social relationships.”

Signs that suggest the dispute is about territory include:

  • The “aggressor” cat will usually chase the “victim” cat
  • One cat may restrict where they go to keep away from the aggressor
  • Vocalizing, hissing, growling, and yowling

Owners often think the cat who is vocalizing is the aggressor, she said, but “most often it is the victim who is doing the vocalization.”

Despite the poor prognosis in cases of extreme social and territorial aggression, there are steps that can be taken in less-severe situations.

“Immediately after a fight, owners must separate the cats until they both calm down. The best way to calm an agitated cat is to put the cat in a darkened room with food, water, and litter box and leave it there,” Dr. Horwitz said. “Keep the cat in the dark until it is calm, which can take hours to several days. The owner can go in only to turn on the light, feed the cat, and then leave.”


The sign the cat may be ready to rejoin the rest of the household is when he or she approaches the owner in a calm manner with a relaxed body posture. Rushing this step can prolong the aggressive stage and may make the problem worse.

“Even after release of the aggressor cat, it may be necessary to create separate areas for food, resting places, and litter boxes for each cat,” Dr. Horwitz cautioned. “Do not cluster these materials together, but spread throughout the environment keeping in mind how the various cats access the space available to them. It also might be helpful for the aggressor to wear a quick release/elastic cat collar with a large bell that will forewarn the victim of their approach allowing escape.”

Additional management and behavior modification approaches may be helpful. Cat owners experiencing these problems are encouraged to seek the help of a board-certified veterinary behaviorist before the intercat aggression is so severe it cannot be remedied.