ate one full-moon night last spring I received a frantic call from one of our very good clients. She had been coming to our clinic for years with both dogs and cats. She had an excellent overall knowledge concerning pets and often had the correct diagnosis made before she reached our clinic. This time however, she was terrified and didn't know what to do.

Her cat had seemingly gone berserk and was chasing and trying to attack the other pets living in the house - including their 80-lb. Golden Retriever. Over the phone, above the agitated voice of the owner, we could hear the loud vocalizations and screams of the cat.

We practice in the forested area of Northern Wisconsin and there is always the potential for our domestic pets to be infected by Rabies or other serious diseases. It turned out that this cat had escaped from the owner's home about 6 weeks before and was gone for several days. The owner was concerned, even though the cat was up to date on all of her vaccinations.

According to the owner, both the dog and the other cat were terrified and the aggression was continuing. All of this had come on suddenly and according to her was getting worse by the minute. We asked her to bring the crazed animal to the clinic that night if she could safely do it.

As she entered the clinic, loud screams emanated from the carrier she held. I took the crate and went into an exam room closing the door behind me. In twenty-some years of practice I've only been bitten once and had no desire for a repeat performance. I put on a pair of heavy gloves and carefully opened the crate door. Out came a large, open and noisy mouth carried by the rest of a calico cat. I expected at least some aggression to be directed at me but there was none. My plan was to observe the cat for a minute before I attempted to physically examine her, but her behavior immediately gave me a diagnosis.

She was loud, and to some would seem frightening, but what she really wanted to do was rub the sides of her body back and forth across my legs. She didn't attempt to bite and after a few minutes lay on the floor on her stomach, meowing loudly and kneading all four feet up and down on the tile. I kept the cat overnight but informed the owner that I believed that the only problem was that her pet was "in heat."

In the spring, female cats respond to the changing of the daylight periods and go into heat on a regular basis every 14 to 21 days and will continue to cycle until fall. This cycling stops immediately if they mate. Typically the cats become vocal, calling for a male cat. She will roll and roll on the ground or floor and constantly rub against furniture, your leg, or another animal. She will often assume a breeding posture with her head and front legs near the ground with her back end elevated. With her feet and claws she will knead at the floor.

Our client's cat was abnormal in that she was forceful to the point of being aggressive and scratching the other animals. With one surgery we eliminated her unwanted heat behavior and helped the cause of pet overpopulation. "Mrs. Hyde" was never seen or heard again.