I have two neutered male cats, six and five years old. They had always gotten along beautifully until a few weeks ago, when they suddenly began fighting. Now, every time they see each other, they hiss, attack each other, and then run away. There is no indication that their behavior is getting better. What can I do?

To understand what is happening with your cats it is helpful to understand the social system of cats. A social system is the group living style that has evolved to ensure optimum survival of the members of a species. Cats seem to have a flexible social system, according to "Aggressive Behavior Between Cats," distributed by the Gaines Corp. It states, "When there is plenty of food and shelter, they can live in large groups. When food or shelter becomes scarce, they divide into smaller groups or become solitary."A group of unsterilized cats generally consists of related females and their kittens. When the male kittens reach approximately one year of age, the tomcat that periodically patrols the area will begin harassing the young males until they leave the family group. Most of the female kittens remain, but occasionally some may emigrate as well. Female social units maintain territories separate from those of other female units. The adult male or tomcat may have a very large territory that encompasses several female territories.

Cats reach puberty or sexual maturity at approximately six to nine months of age. They do not become fully adult, however, until they are two to four years old. At maturity, some cats, even in a well-provisioned household, will become territorial and attempt to expel other cats that they have been living with. This behavior occurs most often between two intact males, occasionally between intact females, and sometimes between neutered animals, either males or females.

Common aggressive behavior in household cats:

Intermale aggression - When males reach adulthood, they may begin challenging one another. Roaming intact tomcats frequently engage in ritualistic threats as well as actual fights. The cats sit very stiffly or stand and stare at each other. They tilt their heads slowly to a 45 degree angle and turn their ears so that the backs of the ears face forward. This posturing is accompanied by growls and very loud howling. Cat owners and their neighbors often hear these vocalization duels occurring outside at night. Then, once cat may leave very slowly, or one or both cats may attack. Sometimes an attack will result in only one bite, but because cat bites frequently become infected, a single bite can be very serious.

Neutering usually stops intermale fighting, particularly if both of the involved males are neutered. The effectiveness of neutering does not appear to be related to the age of the cat or how long he has been fighting. A small percentage of castrated males will still engage in typically male fights.

Next week I will cover more on cat aggression. Areas that I will cover include territorial aggression, fear-induced aggression, how to redirect aggression and introducing new cats or reintroducing cats to each other.

- If you have a question about health, behavior problems, laws, etc., regarding wild or domestic animals, please write Leslie Kelson-Probert, Salt Lake County Animal Services, 511 W. 3900 South, Salt Lake City, UT 84123 or call her at 264-2247.