Castration in Dogs: Health and Behavioral Effects

To neuter or not to neuter your dog? In which cases can it be beneficial and when can it be contraindicated? Is it ethically correct?

Spaying in Dogs Health and Behavioral Effects

As you can see, spaying and neutering is an ideal topic to start a debate. However, many owners find themselves in the position of having to decide, and that's where, sometimes, someone can feel a little lost. So let's answer some questions:

Multiple studies have evidenced that millions of dogs and cats are abandoned or euthanized every year. Some of the main reasons are uncontrolled breeding and the manifestation of behaviors that are annoying to the owner or dangerous for the animal.

Castration affects gonadal steroid hormones directly by removing the main source of testosterone in males and estrogen and progesterone in females, preventing the animal from reproducing. In this way, it works as a population control tool, preventing even more dogs from ending up in shelters or kennels on a daily basis.

Castration, on the other hand, has ramifications for behaviors associated to the reproductive pattern or hormone-dependent processes. As a result, castration in dogs can be used as a solution (or prevention measure) for behavioral issues that are bothersome to the owner and may lead to desertion or euthanasia.

However, the issue is much more complex, and the decision to castrate or not must always go through an exhaustive analysis of the benefits and risks that the operation entails for that particular animal. It is essential to evaluate variables such as age, sex, breed and the conditions in which the dog lives and will live in the long term.

Effects of castration on behavior

Castration and the subsequent hormonal alteration produced in the animal have been related to the reduction of sexually dimorphic behaviors (behaviors fundamentally shown by one of the two sexes, including mating, urine marking, and some forms of aggressiveness). In these cases, we have a starting point for determining whether neutering can improve an animal's welfare. If those behaviors are complicating the owner's life or putting the animal's life at risk (crossing streets to chase females in heat, for example), neutering could be part of the solution. To be more specific:

  • 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 (in the male, removal of the testicles; in the female, removal of the ovaries and uterus) is a common and routine surgical operation, with very low mortality rates or associated complications. However, beyond the timing of the surgery, it is necessary to weigh the long-term risks and benefits. Let's take a step-by-step approach:

It has been shown that spaying significantly decreases the risk of mammary tumors (the most common type of tumor in bitches). Early spaying can help prevent this disease. On the other hand, processes such as pseudocyesis (commonly known as "psychological pregnancy") are eliminated for life.

If the surgery also includes the removal of the uterus, it prevents the development of uterine infections (between 15.2% and 24% of bitches develop pyometra between 4 and 10 years of age) as well as all disorders related to gestation and parturition. However, it is related to an increased risk of urinary incontinence (linked to the level of estrogens in the blood) and also to the risk of obesity.

Let's make a clarification: obesity is the most common nutritional disorder in pets, and being overweight is a risk factor for many serious diseases. Spayed bitches eat more and gain more weight than "whole" bitches, according to data (spaying has not been shown to increase the risk of obesity in male or female dogs). However, through diet and exercise, obesity is controllable, so castration should not compromise the welfare of the animal if proper care is ensured.

As far as testicular and ovarian tumors are concerned, although their incidence is low, castration can be considered as a preventive and curative measure.

In male dogs, this intervention also prevents the possible development of Benign Prostatic Hypertrophy or Benign Prostatic Hyperplasia BPH (enlargement of the prostate that can squeeze the urethra and cause urinary and bladder problems). By the age of 9 years, 95% of uncastrated males have BPH. In any case, it is not a serious problem...

Although there is no evidence that castration increases the risk of diabetes mellitus, the incidence of diabetes mellitus increases by 8.7% in neutered dogs and cats.

Some studies have also revealed an increased risk of hypothyroidism. Fortunately, this disorder is easily controlled with medication.

Finally, it is important to keep in mind that neutering at an early age (before growth is complete) can have consequences associated with bone fracture. The process of long bone consolidation is controlled, in part, by gonadal hormones (sex hormones), and that would be a possible explanation. However, no study has shown this correlation.


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.

The veterinarian has a crucial role, and it is his responsibility to ensure the health and welfare of his patients. Therefore, we should ask him/her to inform us rigorously and objectively about the risks and benefits of the intervention. In this way, we will be able to put aside our subjective impressions and make the right decision.


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