Sexual Aggression In Neutered Cats

In the absence of testosterone, a cat's masculine behavior is not inactive, simply less active.


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Sexual behavior by cats is a pretty gnarly business. A male waits for his moment and then darts after the female, pouncing on her from behind, biting her in the neck and pinning her to the ground, while he intromits his barbed penis. As he withdraws, the backward-pointing spines on his penis lacerate the female’s vagina, causing her to scream and roll away, and she may smack him if he doesn’t get out of range quickly enough.

All in all, a pretty unpleasant sounding experience though, surprisingly, the female will tolerate such ravishes multiple times from multiple suitors when she is at the peak of estrus. Most of us don’t want this type of behavior going on in our homes, and neither do most pet owners want an intact male cat around for other reasons; notably, intact males are generally more aggressive, frequently engage in objectionable marking and mounting behavior, and have a constant eye for the door, particularly when a neighboring queen is in heat. That’s why most cat owners who are not specialist cat breeders gladly accept neutering, in addition to birth control reasons.

Mega Masculine Kitty

As we all know, neutering is very successful in cats at eliminating male-typical behaviors, curtailing most of these behaviors with something like 90 percent efficacy. Many of these male-typical behaviors disappear soon after neutering, though some may persist for weeks, months or even years.

With mounting, at least, prior sexual experience has been shown to persist longer when the neutered male is constantly presented with a female in heat, as you might well expect. But there are other factors operating here, too. It is true that a neutered male is not an “it” but is rather a male lacking significant levels of testosterone.

Masculinization is a process that occurs in utero as fetal testes secrete testosterone and cause masculinization of specific brain regions, particularly the preoptic area of the anterior hypothalamus. This area of the brain is activated by testosterone to produce full red-blooded male behavior. In the absence of testosterone, it is not inactive, simply less active.

I like the analogy of a dimmer switch, by which the light is turned down but not off. It has been shown in rodents but not yet in dogs and cats that a male fetus flanked on either side by other male fetuses can be “super-masculinized” by transamniotic transfer of small amounts testosterone from its two neighbors.

Such a cat (or dog) might have more residual maleness and be more prone to exhibit male-typical behaviors after castration, which brings me to my main point. The various male behaviors that I have described, including inter-male aggression and sexual aggression, may not be completely suppressed and may persist for years following castration of a super-male. It is possible that this explanation accounts for the 10 percent failure rate of neutering in male cats in suppressing all sexually dimorphic behaviors.

Problems With Neutered Males

Now back to the subject of sexual aggression, but this time in neutered males. I have seen several cases of aggression by neutered male cats to females that takes the form of sexual aggression.

Unlike territorial aggression or fear aggression, the pair of cats may get on perfectly well for most of the time but, just occasionally, the male, charges after a neutered female cat, who is clearly not receptive and screams as he launches himself at her from behind, biting her in the nape of the neck and wrestling her to the ground with fur flying—a cookie cutter replication of the sexual act, though not necessarily involving intromission.

I first came to this conclusion many years ago and formulated my own plan for dealing with it. I reasoned that odor is a particularly important sense to a cat and that any self-respecting male should be able to pick up the odor of the same or opposite sex. That is certainly true of an intact male cat who can detect the odor of a female in heat from several blocks away, but a neutered female should not hold the same olfactory attraction.

Nevertheless, by not smelling like a male she could be viewed as a target for the unwanted sexual advances of a neutered super-male Romeo. The antidote for this situation, I surmised, was to play an olfactory trick on the male by making the female smell like a male. This can be achieved quite easily by applying a male pheromone, like androstenone, to the female’s rump every so often.

I happened to have a bottle of this substance from Sigma sitting in my office as a remnant of a pheromone study that I was conducting on litter boxes some years prior and resolved to try it in the next case of sexual aggression I encountered between a neutered male and female cat in a home.

The situation presented itself fairly quickly. The cats in question were an elderly female cat that had been blinded in a fire and a younger amorous, neutered male who engaged precisely in the behavior I just described. I made up a dilution of the androstenone and had the owner apply the pheromone to the female’s rump on a daily basis.

The aggression was stopped in its tracks. He would come screaming around the corner ready to have his way with her when all of a sudden he would stop in his tracks and look puzzled as if to say, “Excuse me, sir, I must have you confused with someone else.”

I successfully used laboratory-grade androstenone to treat presumed sexual aggression in several other cats subsequently before finding a readily available source of androstenone in the form of an aerosol made to help pig farmers detect estrus in gilts. This particular pheromone, which is found in boars’ saliva, is aerosolized and applied to the rump area of the pig. Then, when pressure is applied to the pig’s lower back, she will stand erect ready to be mounted if she is in heat.

The presence of the pheromone makes this pressure test more reliable for estrus detection. Pig farmers also discovered that if the aerosol was applied to the rumps of pigs being mixed in groups, that there was less fighting between them. I imagine this is because each pig on smelling a neighboring pig would consider him well endowed with maleness, a force to be reckoned with and, thus, would keep his distance.

Several of my cat-owner clients have tried using Boar Mate to treat sexual aggression in their cats with the same degree of success that I had with chemical grade androsterone. One even reported that it was only necessary to spray the aerosol onto a pad and gently apply it to the female cat’s rump every other day to keep inter-cat sexual aggression at bay.

I have often wondered whether applying androsterone liberally to the rumps of cats feuding for any reason might be helpful in addressing these sometimes thorny problems of inter-cat housemate aggression, territorial or otherwise. After all, who would pick a fight with any cat wearing androstenone cologne and smelling like Arnold Schwarzecat? As far as the cat is concerned, it may be best to go about one’s business quietly under these circumstances. 

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