Neutering doesn't just prevent animals from being able to produce litters, it moderates temperament, too. By stopping your tomcat's body from producing the male sex hormone testosterone, in most cases his disposition becomes significantly more relaxed. The phenomenon is also true of spayed female cat.
Neutering a Cat
Once male cats hit reproductive maturity, their hormones rule their worlds if they're not neutered, and that manifests in extensive efforts to escape home to look for available female cats, as well as in dangerous physical fights with neighborhood tomcats, loud nighttime vocalization and frustrating urine marking in attempts to communicate through scent with queens. When a veterinarian neuters a cat, she extracts the testicles. This often, but not always, results in a calmer cat.
If part of the reason you love your cat so much is his overall temperament, don't be concerned about neutering changing that. Neutering a cat doesn't alter his disposition, according to the College of Veterinary Medicine at UC Davis. Rather, it usually just makes him a more pleasant version of his old self.
The age at which a cat is neutered determines how drastic the change is in the months following the operation. Physical maturity in cats occurs around 6 months of age. If you neuter a kitten before he's sexually mature, you have the opportunity to halt hormonal patterns before they manifest. Neutering a mature 2-year-old cat may not be as successful in stopping disruptive behaviors as neutering a cat who's just 12 weeks old. If a cat is already in the rhythm of urine-marking, calling out to females and getting aggressive with other males, he may more gradually become less restive. In rare cases, hormonal behaviors don't diminish at all.
Don't expect immediate "nicer" or "calmer" results after neutering your cat. Testosterone doesn't disappear out of a cat's body overnight, even after neutering, and it may take a maximum of 6 weeks or so for his fertility to stop, indicates the East Bay SPCA.
Female Cats and Spaying
Spaying female cats is effective for calming them down and making them seem nicer. By spaying a girl cat, you stop her from going into heat, a natural breeding cycle that involves a lot of restlessness, irritable behavior, "runaway" attempts and persistent crying.