Castration of the male!?!?

Is castration of the male still up to date?

This article has appeared in the magazine Our dog, issue 6, July/August 2019.

The castration of the male, it remains a tricky subject. As we learn more and more about the effects of castration on the health and behavior of the dog, the question arises whether the benefits still outweigh the drawbacks. Because many people no longer see the wood for the trees, this article lists the latest scientific findings.

Why castration?

There are several reasons why people consider having their dogs neutered. The most obvious reason is to make it infertile, so that the dog can no longer reproduce. Other reasons include:

– Reducing aggressive, hyperactive or (hyper)sexual behavior
– The presence of a non-neutered bitch in the household
– Cryptorchidism: when one or both testicles have not descended into the scrotum. – Preventing urination in the house, treating benign prostate enlargement
– Preventing or treating tumors of the testicles (testicular cancer) and perianal gland tumors
– Treating excessive discharge from the penis

It is true that in some cases castration certainly has or can have benefits. In practice, however, it does not always appear to have the desired effect on behaviour. It is even possible for the behavior to be exacerbated by neutering. In addition, there is increasing evidence that castration has a negative influence on the development of the body and that certain forms of cancer are more common in neutered dogs.

Castration in humans

Looking at the effects of neutering on humans, it may come as no surprise that losing key testosterone sources can cause all sorts of problems in dogs as well.

From an article in Fidelity: “In the longer term, the production of blood cells is also disrupted, which leads to anemia. The bones become brittle. Many men without testes also develop diabetes. And their body fat gets a more feminine distribution: less on the stomach, more on the hips. […] If a boy is castrated before puberty, the consequences are even more serious. All secondary sex characteristics then remain absent. That means: no hair on the face, in the pubic area or on the chest; no seed production; no beard in throat; few muscles and a small penis. The bones continue to grow for extra long, because they do not receive a signal to stop. This explains why castrati—singers who were emasculated in earlier centuries to preserve their high-pitched voice—were described by contemporaries as clumsy giants.”

As we will see, these findings are similar to results from scientific research into the possible consequences of male castration. The most notable results regarding the musculoskeletal system, cancer, behavior and health are briefly summarized below. The dates of the studies concerned are indicated in brackets after each result.

Effects on the musculoskeletal system

– In a study of 1444 Golden Retrievers, dogs neutered when they were less than a year old were significantly taller than dogs neutered after that age (1998-1999)

– A study of 203 agility dogs showed that the shinbone (tibia), radius (radius) and ulna were significantly longer than the thighbone (femur) and humerus (humerus) in dogs neutered at or before the age of 8 months, compared to intact dogs (Chris Zink, see source material)

– Cruciate ligament ruptures (ruptured anterior cruciate ligament) are significantly more common in neutered dogs, even when body size is taken into account (1993, 1999, 2004, 2007, 2017)

– In a study of 759 male and female Golden Retrievers neutered before 6 months of age, 5% males and 8% females had cruciate ligament ruptures. There were no cruciate ligament ruptures in the unneutered dogs (2013)

– Dogs neutered at least six months prior to hip dysplasia diagnosis were one and a half times more likely to develop hip dysplasia than sexually intact dogs (2005)

– Neutered dogs had a 3.1 times higher incidence of patellar luxation (dislocation of the kneecap) (2005)

– In Labrador Retrievers and Golden Retrievers neutered before 6 months of age, joint disease was two and four to five times more common, respectively (2014)

– In a study of 1170 German Shepherds followed up to the age of 8 years, 21% of the neutered males was diagnosed with one or more joint disorders, compared to 7% of the intact males (2016)


These results clearly show that the age at which a dog is neutered can influence the development of joint disorders. This has to do with, among other things, the bone structures of the growing dog. A puppy's long bones grow from soft areas on either end; so they do not grow over the entire length. The pieces of cartilage at the ends of the long bones that provide growth in length are called growth plates or discs.

These contain rapidly proliferating cells that cause the bones to elongate until the end of puberty. As puberty approaches, hormonal changes signal the growth plates to close. Closure of the growth plates is usually complete by the time the dog is about 18 months old. As long as the growth plates are not yet closed, they are still soft and vulnerable.

What happens if you neuter a dog before the growth plates have closed? Due to the disappearance of the sex hormone testosterone, signals are no longer given that 'tell' the growth plates that they have to close. This can cause the bones to continue to grow at an abnormal rate and/or cause the bones to become out of proportion to each other. Dogs neutered during or before puberty can often be recognized by their longer limbs (lanky males), lighter bones and narrower chest and skull.

It is not difficult to imagine that abnormal bone growth can lead to the development of various joint diseases. It should be noted that the weight of the dog after castration can also play a role: it is known that neutered dogs are more likely to be overweight or obese because their metabolism changes. This can contribute to the development of orthopedic disorders.

Finally, a lack of testosterone has a significant negative effect on the build-up of muscle mass. This can no longer develop optimally or decreases after castration, so that the male can usually not grow into a nicely built dog with good muscling (again: lanky). This in turn can contribute to the development of all kinds of joint problems and injuries.

Effects on the development of various cancers

– A study found a 1.6 times greater risk of cardiac haemangiosarcoma (malignant tumor of the blood vessel wall at the base of the heart) in neutered dogs compared to intact male dogs (1999)

– Male Rottweilers neutered before the age of one year were 3.8 times more likely to develop bone cancer than intact dogs (2002)

– Neutered dogs had a 2.2 times higher risk of developing bone cancer than intact dogs (1998)

– Neutered dogs had a 2.8 times higher risk of developing prostate cancer than intact dogs (2007)

– Neutered dogs had a 4.3 times higher risk of developing prostate cancer than intact dogs (2002, 2003)

– Neutered dogs had a 3 to 4 times greater risk of developing bladder cancer than intact dogs (2000, 2007)

– In early neutered male Golden Retrievers, the risk of lymphosarcoma (malignant tumors in the lymph tissue) was three times greater than in intact male dogs (2013)

– In a study of 2,505 Vizslas, neutered dogs at any age were found to have a significantly higher risk of mast cell cancer, hemangiosarcoma (tumor of the blood vessel wall), lymphoma and all of these cancers combined than intact dogs. The younger they were at the time of castration, the earlier they were diagnosed with these diseases (2014)

Effects on Behavior

– An association has been found between castration at a young age and an increased risk of fear of noises and unwanted sexual behavior such as mounting other dogs (2004)

– Vizslas neutered before six months of age, between seven and 12 months of age or older than 12 months had a significantly increased risk of developing storm fear. The dogs that were neutered before the age of six months had an increased chance of developing a conduct disorder (2014)

– Significantly more behavioral problems were observed in neutered males than in intact males. Aggression in particular occurred regularly (2005, 2006)

– German Shepherds neutered between the ages of five and ten months were much more likely to show reactive behavior (2006)

– In a recent study of more than 13,500 dogs, no association was found between neutering and aggression towards known people and other dogs. However, there was a significant increase in the likelihood of moderate or severe aggression towards strangers in dogs neutered between the ages of 7 and 12 months (2018)

Other health effects

– Some males had an increased risk of incontinence if they were neutered before puberty (1996)

– A health study involving several thousand Golden Retrievers showed that neutered dogs were more likely to develop hypothyroidism (underactive thyroid). Similar results emerged from other studies (1994)

– The risk of side effects from vaccinations was 27% to 38% greater in neutered dogs compared to intact dogs (2005)

– A study of 90,090 dogs revealed that neutered dogs had a significantly increased risk of atopic dermatitis (chronic skin condition), autoimmune hemolytic anemia (a disease in which the red blood cells are broken down by antibodies directed against their own blood cells), Addison's disease , underactive thyroid, immune-mediated thrombocytopenia (platelet breakdown), and inflammatory bowel disease (2016)

While some of the above studies are already somewhat outdated and the methods and implementation of others can undoubtedly be questioned, they are findings that we cannot or should not just ignore. In addition, research on the subject is still ongoing and the evidence that neutering can have a serious negative impact on a dog's health and well-being is likely to continue to pile up.

More and more behavioral experts and veterinarians are advocating that a dog should only be castrated if there are urgent medical reasons for this, such as in the case of testicular cancer or if aggression is demonstrably influenced by testosterone.

It is important that the individual case is always considered and that castration is not simply resorted to because it is so often regarded as a common 'solution'. Instead of this irreversible choice, one can also consider using behavioral therapy and/or supported medication when treating problematic behaviour; in the long run, this usually provides much better results.


If, despite the risks and despite the lack of urgent medical reasons, one decides to have the dog castrated, it is advisable to wait until its growth plates have closed. This is usually at the age of 18 months. An X-ray may be taken to be sure. It is even better to wait until the dog has reached not only physical but also emotional maturity. In most dogs this happens when they are between three and four years old.

In any case, early castration is increasingly strongly discouraged; the advantages no longer outweigh the obvious disadvantages. In addition to the arguments already mentioned, very young puppies also have a higher risk of anesthesia and a higher chance of developing hypothermia (hypothermia) and hypoglycemia (low blood sugar).

Economic motives

Unfortunately, economic motives still play a role in spaying at a young age. The KNMVD (Royal Dutch Society for Veterinary Medicine) says about this, for example: “In breeding, puppies are sometimes neutralized at the age of six to eight weeks at the breeder's request. Because these breeders of certain special breeds only sell castrated puppies, they maintain a monopoly position in the market. […] Due to the intention behind the intervention (economic interests of the breeder) and the risks, neutralization at a very young age is not acceptable in this case.”

It is also possible that breeders stipulate in a contract that a puppy should be neutered as soon as possible. In such a case, puppy buyers would do well to ask themselves whether it is wise to purchase a puppy from the relevant breeder. To reiterate the old adage, "Look before you begin."

Source material:

KNMvD's position on early castration:

Jane Messineo (2018) Should I spay or neuter my Dog? – Understanding the secret life of sex hormones

Sander Becker (2012) Much medical suffering after castration. In: Trouw

Chris Zink (2018) Gonadectomy – Rethinking Long-Held Beliefs. See:

Schaefers-Okkens AC, Overgaauw PAM. (2007) Neutralization of puppies and kittens at a very young age. Journal of Veterinary Medicine

Farhoody, P., Mallawaarachchi, I., Tarwater, PM, Serpell, JA, Duffy, DL & Zink, C. Aggression toward familiar people, strangers, and conspecifics in gonadectomized and intact dogs. Frontiers in Veterinary Science

This article appeared in Onze Hond magazine, issue 6, July/August 2019