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Benefits of Spaying and Neutering Pets
May 15, 2025
Neutering refers to the surgical or chemical sterilization of an animal, so they are unable to reproduce, and do not exhibit mature, sexual behavioural and characteristics. Spaying is the term commonly used for an "ovariohysterectomy," the surgical removal of the entire reproductive system including the uterus and ovaries, while castration refers to removal of the testes. Ovariectomy (removal of only the ovaries in a female) is a less common surgical procedure that attains the same results.
Spaying and neutering are safe and reliable methods of birth control in female dogs and cats. As humane societies and animal shelters are overwhelmed with homeless and abandoned animals, spaying and neutering is an important way we can be responsible pet owners and not contribute to pet overpopulation.
In addition to pet overpopulation, spaying a female dog means that the (often overlooked) risks associated with pregnancy are removed. Pregnancy complications can range from the need for surgical intervention (i.e. Cesarean sections), infections (i.e. mastitis), to the death of the pregnant animal or her offspring.
Spaying a pet will also ensure behavioural and environmental “problems” associated with heat cycles are avoided. For example, in dogs, the bloody discharge from the vulva, which can persist for two to three weeks during each heat period, can result in bloodstains around the house. This problem is further complicated by the fact that they must be kept indoors or be closely supervised when outdoors to prevent the unwelcome approaches of males. In cats, the excessive vocalization and behaviour changes associated with heats are also avoided in spayed animals. If not mated, female dogs may also experience "false pregnancy," a condition wherein they behave as if pregnant, complete with whining, restlessness and lactation (milk production) even though no pregnancy has occurred.
In male animals, castration reduces the risk of aggression (especially in dogs) and urine marking (in dogs) or spraying (in cats). It will also remove the strong “tom cat” smell that many people find extremely unappealing. While cats that are neutered young will rarely spray, late neutering may not stop spraying in all animals who have already started this behaviour.
Female dogs and cats run an increased risk of developing life-threatening medical problems later in life if they are not spayed. Specifically, pyometra, or uterine infections, occur commonly in older intact bitches, and can require life saving surgery or intensive medical management. This cannot occur in animals without ovaries.
Spaying a dog before its first heat greatly reduces the risk of mammary tumours. Studies have shown that the risk of mammary cancer in female dogs increases significantly with each successive heat period until the age of two years. After two years of age, spaying does not really make any difference in the incidence of mammary cancer, though it is often still recommended in dogs with mammary tumours. The data in cats is less definitive than in dogs, however spaying before the first heat is well established to dramatically reduce the risk of mammary cancer. While mammary tumors in dogs may be benign or malignant, in cats almost all (more than 90 per cent) of mammary cancer is malignant and so early spaying dramatically reduces the risk of this fatal condition.
There are several possible downsides to sterilization of animals. Surgery always carries some degree of risk, however in healthy young animals this risk is incredibly low. However, some animals may have conditions (for example, severe cardiac disease, hemophilia, etc.) that make surgery more complex; in these cases, consultation with specialists is recommended.
There is data to suggest that early sterilization may be associated with an increased risk of certain conditions, especially bone diseases, in large breed dogs. This seems to be much less of a concern in cats and small breed dogs. In these animals, the risks of early sterilization must be weighed against the benefits (lower risks of mammary cancer, pyometra, pregnancy, etc.). Conversation with a veterinarian is recommended to decide on the best course of action.
While sterilization does alter hormonal profiles in dogs and cats, it is unclear if this increases the risk of obesity. Obesity in pets is usually the result of overeating and a lack of exercise, and so indoor, sterilized animals require strict calorie control. Similarly, sterilization does not change a pet's personality or temperament, rather it prevents the development of sexually mature behaviours.
Dr. Matthew Kornya, BSc, DVM, DVSc, DACVIM (SAIM), Resident ACVECC
Consulting Editor
March 2025