Spaying in Dogs: Health and Behavioral Effects of Castration

The topic of spaying and neutering your dog is a complex one with many factors to consider. Numerous studies have shown that millions of dogs and cats are abandoned or euthanized each year, often due to uncontrolled breeding or troublesome behaviors.

Removing the main source of testosterone in males and estrogen and progesterone in females through castration directly impacts gonadal steroid hormones, preventing reproduction and serving as a population control method that can reduce the number of animals in shelters and kennels.

However, castration also affects behaviors associated with reproductive and hormone-dependent processes, making it a possible solution or prevention measure for behavioral issues that could lead to abandonment or euthanasia.

To make an informed decision about whether to spay or neuter your dog, it's crucial to conduct a thorough analysis of the individual animal's age, sex, breed, and living conditions. This will help determine whether the benefits of castration outweigh the risks for that particular dog.

Spaying in Dogs Health and Behavioral Effects

Effects of castration on behavior

Castration in dogs has been linked to a reduction in sexually dimorphic behaviors, such as mating, urine marking, and certain forms of aggression. This presents an opportunity to evaluate whether neutering can improve a dog's overall well-being. If these behaviors are causing difficulties for the owner or putting the dog's safety at risk (such as crossing roads to pursue females in heat), neutering may be a viable solution. To elaborate further:

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

However, castration cannot be expected to completely eliminate aggressive behaviors since many types of aggressiveness have environmental causes or are related to learning processes. It is important to be clear on this point so as not to create false expectations.

On the other hand, inactivity and lethargy have sometimes been associated with castration in females. However, research has not been able to demonstrate whether these changes in activity level are simply due to the increase in age of the animal. What has been shown is that, in those bitches that have shown competitive aggressiveness, spaying may be contraindicated; these bitches, once spayed, may become more aggressive.

Finally, it is necessary to clarify that castration does not interfere with the ease of training and does not influence the performance of working dogs.

Castration in 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 just the timing of the surgery. Let's examine each factor in detail:

Spaying female dogs significantly reduces the occurrence 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 like pseudocyesis (also known as "false pregnancy") for life.

If the surgery involves removing the uterus, it can prevent uterine infections (pyometra), which affect between 15.2% to 24% of bitches between 4 and 10 years old, as well as all gestation and parturition-related disorders. However, it is associated with an increased risk of urinary incontinence (related to the level of estrogens in the blood) and obesity.

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

Castration, in 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, castration also prevents the development of Benign Prostatic Hypertrophy (BPH), which affects 95% of uncastrated males by the age of nine. Although not a severe problem, BPH can cause urinary and bladder issues due to prostate enlargement that compresses the urethra.

While there is currently no evidence that castration 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 have bone fracture consequences due to the role sex hormones play in long bone consolidation. However, no study has demonstrated a correlation between neutering and bone fractures.


There are no absolute truths on a subject as complex as the relationship between spaying and neutering and animal welfare. However, being well informed and thoroughly assessing the characteristics of our dog or bitch will help us to make the best possible decision.

As a crucial figure in animal health and welfare, veterinarians hold the responsibility of informing pet owners objectively and rigorously about the risks and benefits of an intervention. By seeking information from a veterinarian, pet owners can set aside subjective impressions and make informed decisions that prioritize their pet's well-being.
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