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Neutering Your Dog: Health & Behavior Benefits (Castration)

The decision to spay or neuter your dog is a complex one with many factors to consider. Millions of dogs and cats are abandoned or euthanized each year, often because of uncontrolled breeding or behavioral problems.

Spaying or neutering directly affects their reproductive hormones by removing testosterone in males and estrogen and progesterone in females. This prevents reproduction and helps control pet populations, reducing the number of animals in shelters.

However, spaying or neutering also affects behaviors related to reproduction and hormones. This can be a solution or prevention for behavioral problems that may lead to abandonment or euthanasia.

To make an informed decision, consider your dog's age, sex, breed, and lifestyle. This analysis will help you determine if the benefits of spaying or neutering outweigh the risks for your individual dog.

Spaying in Dogs Health and Behavioral Effects

Behavioral effects of neutering in dogs

Neutering in dogs has been associated with a reduction in sexually dimorphic behaviors such as mating, urine marking, and certain forms of aggression. This provides an opportunity to assess whether spaying or neutering can improve a dog's overall well-being. If these behaviors are causing difficulties for the owner or posing a risk to the dog's safety (e.g., crossing roads to chase females in heat), spaying or neutering may be a viable solution. To elaborate:

  • In dogs, neutering reduces intrasexual (male-male) aggression by more than 60%, urine marking by 50%, and roaming behavior (dangerous to the animal due to risks such as the possibility of being run over) by up to 90%.
  • If surgery is performed before puberty or first copulation, it typically prevents mating and copulatory behavior for the rest of the animal's life.
  • According to some authors, castrated males also have a lower incidence of aggression toward humans (Overall and Lowe 2001).

However, it's important to understand that castration cannot be expected to completely eliminate aggressive behavior, as many types of aggression have environmental causes or are related to learning processes. Clarity on this point is crucial to avoid creating false expectations.

On the other hand, inactivity and lethargy have sometimes been associated with neutering in females. However, research has not been able to determine whether these changes in activity levels are simply due to the animal's increasing age. What has been shown is that spaying may be contraindicated in those female dogs that have shown competitive aggressiveness; these dogs may become more aggressive after spaying.

Finally, it's important to note that spaying or neutering does not affect the ease of training or the performance of working dogs.

Spaying and neutering of dogs: health effects

Castration in dogs health effects

Castration is a routine surgical procedure with low mortality and complication rates. However, it's important to consider the long-term risks and benefits beyond the timing of the surgery. Let's look at each factor in detail:

Spaying female dogs significantly reduces the incidence of mammary tumors, which are the most common type of tumor in bitches. Early spaying can help prevent this disease. However, spaying also eliminates processes such as pseudocyesis (also known as "false pregnancy") for life.

If the surgery includes removal of the uterus, it can prevent uterine infections (pyometra), which occur in 15.2% to 24% of bitches between the ages of 4 and 10, as well as all pregnancy and parturition-related problems. However, it is associated with an increased risk of urinary incontinence (related to estrogen levels in the blood) and obesity.

It's worth noting that obesity is the most common nutritional disorder in pets, and overweight dogs are more likely to develop serious diseases. Research shows that spayed female dogs tend to eat more and gain more weight than unspayed females. However, obesity can be controlled through diet and exercise, so proper care can ensure that the animal's welfare is not compromised.

Spaying and neutering of both male and female dogs can be considered a preventive and curative measure against testicular and ovarian tumors, although their incidence is low.

In male dogs, neutering can prevent the development of Benign Prostatic Hypertrophy (BPH), which affects 95% of unneutered males by the age of nine. Although not a severe problem, BPH can cause urinary and bladder issues due to the enlargement of the prostate that compresses the urethra.

While there is currently no evidence that neutering increases the risk of diabetes mellitus, the incidence of this disease increases by 8.7% in neutered dogs and cats.

Some studies have also shown an increased risk of hypothyroidism, but this disorder is easily managed with medication.

Lastly, it’s essential to consider that neutering at an early age (before growth completion) may lead to bone fracture consequences due to the role sex hormones play in long bone consolidation. However, no study has demonstrated a direct correlation between neutering and bone fractures.


There are no absolute truths on a topic as complex as the relationship between spaying and neutering and animal welfare. However, being well-informed and thoroughly evaluating our dog's characteristics will help us make the best decision possible.

As key players in animal health and welfare, veterinarians have a responsibility to inform pet owners objectively and rigorously about the risks and benefits of a procedure. By seeking information from a veterinarian, pet owners can set aside subjective impressions and make informed decisions that put their pet's well-being first.