Most male animals that are kept for companionship, work, or food production (horses, dogs, cats, bulls, boars) are neutered (castrated) unless they are intended to be used as breeding stock. This is a common practice to prevent unacceptable sexual behaviour, reduce aggressiveness, and prevent accidental or indiscriminate breeding. The intact male (tomcat) is likely to roam, fight with other males, and spray and is of course, strongly attracted to seek out and mate with intact females. Tomcat urine is particularly odorous. Overall the intact male cat can make a most unpleasant household companion.

How does castration affect behaviour?

The only behaviours affected by castration are those under the influence of male hormones (sexually dimorphic behaviours). A cat’s temperament, training, and personality are the result of genetics and upbringing, and are generally unaffected by the presence or absence of male hormones. Castration is unlikely to calm an overactive cat or decrease aggression toward people. Since the male brain is masculinized by the time of birth, castration will reduce some, but not all of the sexually dimorphic male behaviours. If performed prior to sexual maturity castration will help to prevent the development of secondary sexual characteristics such as penile barbs, large jowls and glands at the dorsal part of the cat’s tail.

What is neutering?

The operation of neutering or castration of male cats is called an orchidectomy. The procedure involves general anaesthesia, and an incision is made over each side of the scrotal sac so that each testicle can be excised. External sutures are not generally required. In males both testicles descend prior to birth from inside the abdominal cavity through the inguinal canal into the scrotal sac. In some cats one or both testicles do not descend fully into the sac and may either remain in the abdomen or anywhere along the inguinal canal path to the scrotal sac. These cats are called cryptorchid and a more extensive surgery will be required to locate the testicles and remove them. If these testicles are not removed they will continue to produce hormones and the behaviour problems associated with intact male cats. Vasectomies are not performed in cats. It is both sterilization and removal of the male hormones that provide the behavioural benefits.

What are the benefits of neutering?

Population control

Millions of cats are destroyed across North America each year because there are far more cats born than homes available. A single male cat can father many litters so that neutering of intact males is essential for population control. Although sexual desire will be greatly reduced by castration, some experienced males may continue to show sexual interest in females.


The most common behaviour problem in cats of all ages is indoor elimination at locations other than the litter box. A large number of these cases are cats that spray or mark walls and other vertical household objects. Adult male cats have an extremely strong urge to mark territory, both indoors and out. Neutering reduces or eliminates spraying in approximately 85% of male cats.


Cats, whether neutered or intact, can get into fights but most inter-cat aggression is seen between intact males. This is a direct result of competition between male cats, and because intact male cats roam and protect a much larger territory. If these fights lead to punctures that penetrate the skin abscesses are a common sequel. Neutering reduces fighting and abscess development in male cats.

Roaming and Sexual Attraction

Intact males have much larger territories and wander over greater distances than females and neutered males. The urge to roam may be particularly strong during mating season. Castration reduces roaming in approximately 90% of cases. Neutering greatly reduces sexual interest, but some experienced males may continue to be attracted to, and mate with females.

Physical Changes

Male urine odour is particularly strong and pungent. Castration leads to a change to a more normal urine odour. Many owners claim that their intact males become much cleaner, less odorous, and better self-groomers after neutering. Abscess formation as a result of fighting is far less frequent and some of the secondary sexual characteristics such as the over-productive tail glands in the condition known as “stud tail” can be dramatically improved.

Does neutering lead to any adverse effects on health or behaviour?

There are many misconceptions about the effects of neutering on health and behaviour. Neutered males are no more likely to become fat or lazy provided they receive a proper diet and adequate exercise. With less roaming, fighting, mating, calorie intake may have to be reduced and alternative forms of play and activity provided. Behaviours that have developed independent of hormonal influences such as hunting are not affected. Regardless of age at which it is performed, neutering does not have any effect on physical development, (overall height and weight, urethral size). Although neutering prior to puberty appears to have similar effects to neutering post-puberty, every attempt should be made to neuter prior to puberty before the cat develops new problems, experiences and habits.