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Castration in Dogs - What, When, Why?

Updated: Jul 8

Key Words:

Gonad: Sex gland (testis or ovary)

Testes: The male gonad

Castration: The excision of the gonads

Orchiectomy: The excision of one or both testes

Gonadectomy: Removal of a gonad

Entire: Relating to an animal that has not had its gonads removed, also can be called ‘unaltered’. 

During the article, we will be focusing on castration, relating to male dogs, but occasionally research uses ‘gonadectomy’ to refer to both male and female gonad removal. 

WSAVA Guidelines for the Control of Reproduction in Dogs and Cats

Recently, the World Small Animal Veterinary Association (WSAVA) released reproduction guidelines for cats and dogs. The trends in castration of male dogs (orchiectomy/gonadectomy) has long been a topic for discussion. Why do we do it? When should we do it? Does it impact our dogs' behavioural, mental and physical health? Does advice change with different breeds?

The best options for reproduction control in dogs and cats are the ones that have the least long- term health concerns which may be more pronounced particularly in large and giant breed dogs (Benka et al., 2023).”

WSAVA Guidelines for the Control of Reproduction in Dogs and Cats Summary: 

What is surgical castration?

Surgical Castration is the surgical removal of the male reproductive glands (gonads), testicles, from a male dog.  

Historically, veterinary professionals may have been tempted to give blanket advice to castrate, maybe before sexual maturity, to prevent unwanted sexual or hormonal driven behaviour and unplanned litters. But, there is more to it than that and we have more and more evidence coming out that allows us to make more individualised and informed decisions about if castration is right for each individual dog. 

When are we suggesting castration?

The decision if a dog or cat is to be spayed, neutered or otherwise being rendered infertile is influenced by several factors. While temperament traits or preexisting health conditions may influence benefit and risk assessments for an individual animal, it is important to discuss the setting in which the decision is being made as well as the setting the animal lives in or will likely live in. J-of-Small-Animal-Practice-2024-Romagnoli-WSAVA-guidelines-for-the-control-of-reproduction-in-dogs-and-cats.pdf

A recent survey by Veterinary Voices UK looked at neutering habits of UK veterinary professionals, by splitting dogs into size categories and asking at what age people advise of castration based off weights in KG:

  • Toy <5

  • Small 5-10

  • Medium 10-25

  • Large 25-40

  • Giant 40+

In the survey of nearly 400 veterinary professionals in Veterinary Voices UK Community, when asked ‘What age do you suggest performing castration?’ In relation to different size categories of dogs e.g., Toy/Small, Medium, Large and Giant on ALL accounts, 40% of veterinary professionals answered that they do not advise castration unless behaviourally or medically indicated. Furthermore, 12% also answered ‘Other’ and went on to use phrases such as, ‘Breed, lifestyle and owner dependent - discuss pros / cons with owners to help them make an informed decision’, ‘nurse discusses and assesses behaviour prior / on admit to neutering and if any doubts then a behaviourist and postponement is recommended’ and ‘Temperament dependent’.

So, over half of veterinary professionals who answered no longer recommend castration as a blanket rule, and used individual dog's factors to assess. 

Additionally, for those that did suggest ages for castration, the bigger the size bracket of the dog e.g, toy - giant, the older the age bracket suggested, suggesting that these professionals still took the growth and maturity of their male dogs as important in decision making. 

Why would we, or wouldn't we suggest castration? 

There are a number of reasons we should take into consideration when making a decision on castration for our pet dog.

  1. Do we need to do so for population control e.g., do we have to prevent unplanned litters?

  2. Are there any behaviours present that would be made better or worse by castration?

  3. Is there any medical indication to castrate?

  4. Is there any medical indication not to castrate?

  5. Is my breed at a particular risk or predisposed to certain issues?

  6. Am I aware of the pros and cons of surgical castration?

Medical reasons for and against castration

As with all considerations, we should be weighing up our pets on an individual basis, weighing up the risk V benefit and assessing the viable options such as leaving entire (unaltered), offering surgical castration, offering medical castration (implant) or exploring other options. 

Surgical castration could reduce Testicular neoplasia, Benign prostatic hypertrophy, prostatitis, Perianal adenomas and perineal hernias. However, it could increase Prostatic neoplasia, Lymphoma, Cranial cruciate ligament and hip dysplasia and obesity.

The WSAVA reproductive guidelines comments on testicular disease, prostate gland disease, perianal gland tumours, transmissible venereal tumours, urethral prolapse, perineal hernias and behavioural concerns.

Perianal gland tumours  (castration decreases risk)

Perianal gland tumours rank third among all types of male dog tumours. Hormonal stimulation in older adult, entire male dogs may induce hyperplasia (overgrowth) of the perianal glands or their neoplastic transformation. Hormonal factors associated with the entire males were suggested as important causative factors responsible for a neoplastic progression. According to previous reports, a ‘long-term biological exposure’ to testosterone in entire male dogs is considered to result in an increased risk of the development of perianal gland tumours. Significantly better therapeutic effects of both surgical removal of neoplastic lesions and orchidectomy (castration) in male dogs rather than a single surgical removal of a tumour have been documented.

The WSAVA states that Gonadectomy is an effective treatment for adenomas and epitheliomas. Anti- hormonal therapy is beneficial in case of adenomas. 

Anecdotal evidence indicates that GnRH agonists may be an effective way of treating perianal gland adenomas and epitheliomas.

Prostate Gland Disease

Benign Prostatic Hyperplasia (BPH) is one of the diseases that is seen more commonly in entire male dogs. Benign prostatic hyperplasia (BPH) is a natural consequence of ageing thought to affect over 80 per cent of entire male dogs over the age of five. Since the enlarged prostate is dependent on testosterone, traditional treatment has involved removing the testosterone, either through the use of surgical castration or the administration of progestogens, which decrease testosterone through negative feedback on the hypothalamic-pituitary- gonadal axis. The WSAVA states that medical therapy to decrease prostate gland volume including anti- androgens and long- term GnRH agonists (if available), or gonadectomy will be curative in dogs with signs of BPH. Gonadectomy or chemical castration will also prevent development of BPH. 

Prostatitis is an inflammatory disease of the prostatic parenchyma that occurs independent of age and is frequently caused by bacterial infections ascending via the urethra or spreading via the blood circulation. The effect of anti-androgen treatment may help in reaching a decision on gonadectomy; the option of gonadectomy should be discussed in case of recurrence. The use of long- acting GnRH agonists may potentially have a similar effect although there is as yet no evidence for their advantage over gonadectomy. The WSAVA states that Gonadectomy is a useful, accompanying measure to resolve and prevent prostatitis.

Prostatic Neoplasia is very low risk, less than 1% risk of developing in entire males, however In dogs, gonadectomy is the largest risk factor for the development of prostate Adenocarcinoma. Luteinizing hormone receptors are abundant in the prostate gland and increase in expression following gonadectomy.

With clients opting to keep their male dogs intact the WSAVA suggests a regular complete andrological exam (which should include rectal palpation, prostatic ultrasound and assay of serum CPSE) to be repeated at least once/ year from when the dog has reached 40% of his life expectancy. 

Testicular cancer

Testicular tumours are the most common neoplasms in the male reproductive system in entire male dogs, canine testicular tumours account for about 90 % of cases of cancer of the reproductive tract. Cryptorchidism (an undescended testicle) and age are the main predisposing factors for the development of canine testicular tumours.

Luteinizing Hormone Impact (increased risk with castration)

An area of growing interest is the impact of Luteinizing Hormone (LH) on a dog after castration.

‘Research is in its infancy and there is no direct proof that there is a causative connection between elevated LH concentration and the long-term adverse health effects of castration.’

One of the most interesting reviews is by Michelle A. Kutzler (2020) in the review ‘Possible Relationship between Long-Term Adverse Health Effects of Gonad-Removing Surgical Sterilization and Luteinizing Hormone in Dogs.’ which covers a number of conditions and how LH could impact them.

In the normal adult dog, an area in the brain called the hypothalamus secretes gonadotropin-releasing hormone (GnRH). GnRH then stimulates another area in the BRAIN, the anterior pituitary gland, to release luteinizing hormone.

Luteinizing hormone (LH) stimulates the secretion of gonadal steroid hormones, testosterone in males, and these gonadal steroid hormones then negatively feedback to the brain in the hypothalamus and anterior pituitary to decrease the secretion of GnRH and LH, respectively. This cycle continues continuously. 

However, in surgically castrated dogs where the testicles have been physically removed, there is no negative feedback. This results in higher circulating levels of luteinizing hormone than usually exist in a dog's body. In these cases, LH concentrations are more than thirty times the concentrations found in normal adult dogs.

Although the main role of LH is for reproductive functions there are LH receptors present throughout the body, not just limited to the reproductive tract, so these high levels of LH may impact other areas too.

  • LH and Obesity: LH could have an impact on obesity in castrated dogs, due to the change in appetite and metabolism. In entire (non - castrated) dogs, food intake suppresses the secretion of gastrointestinal hormones (cholecystokinin and glucagon),resulting in satiety (alleviation of hunger). Although it important to note that we do not know for certain, It is possible that stimulation of LH receptors (present in the gastrointestinal tract following gonadectomy) increases cholecystokinin and/or glucagon release and that LH receptors in the hypothalamus are involved in the increase in appetite. 

  • LH and Urinary Tract: Another possible impact is on the urinary tract, under normal circumstances, there is a balance of urinary calculi promoters and inhibitors. However, this balance appears to be disrupted from the influence of an abundant LH environment resulting in increased Urinary calculi risk. After evaluating records from more than two million dogs, Banfield Pet Hospital found that all urinary calculi (urine crystals, kidney stones, and bladder stones) occurred at a rate three times higher in neutered dogs compared with entire dogs.

  • LH and Endocrine disorders: Endocrine disorders such as hypothyroidism and diabetes mellitus may also be at increased risk from gonad removal (surgical castration). 

  • LH and Hip Dysplasia: The negative effect of gonadectomy at <6 months of age or <12 months of age on joint health has been reported in large populations of male and female dogs, and certain breeds. Compared to entire dogs, gonadectomy increases hip dysplasia by 1.5-2 times the occurrence in entire dogs. The incidence of hip dysplasia is strongest in neutered male dogs as opposed to spayed female dogs. It has been demonstrated that there is expression of LH receptors within the ligament of the head of the femur, the hyaline cartilage,and subchondral bone of the femur head.It is possible that, in some dogs, an increase in LH receptor activation in the structural support tissues within the hip joint results in increased laxity, which is responsible for the higher occurrence of hip dysplasia in spayed and neutered dogs but data is not sufficient to draw this claim at present.

  • LH and cranial cruciate ligament ruptures: Similar to hip dysplasia, most dogs with cranial cruciate ligament ruptures are born with normal stifle joints but then develop the tendency for cranial cruciate ligament rupture secondary to intrinsic and/or extrinsic factors. Removal of the sexual organs (gonads) significantly increases the prevalence of cranial cruciate ligament rupture. Neutering before puberty delays tibial growth plate closure, which extends the length of tibia and the steepness of the tibial plateau - as per the survey of Veterinary Voices UK respondents, prepubertal castration was not recommended by respondents, with the majority advising to not castrate unless medically or behaviourally indicated. However, even dogs that are gonadectomized between 6 and 12 months have an increased risk for cranial cruciate ligament rupture so care in timings must still be taken with castration timings. It is possible that an increase in LH receptor activation in the cranial cruciate ligament results in increased laxity, which is responsible for the higher occurrence of ligament ruptures in spayed and neutered dogs.

Despite the fact that LH could have an impact on a number of other body systems and we are still learning more about this, it is important to note that research is in its infancy and  there is no direct proof that there is a causative connection between elevated LH concentration/LHR expression and the long-term adverse health effects of spaying/neutering.

Other cancers

There are some cancers where sex status, sex and the impact of LH has been hypothesised to contribute to the increased risk of development. As with anything, the development of many of these cancers are multifactorial, and therefore no strong conclusions can be drawn.

To read more about male dog tumours, read 5.2 of the WSAVA guidelines, but a few will be discussed below. 

  • Osteosarcoma is a highly metastatic cancer of bone tissue. An increased risk for osteosarcoma following gonadectomy has been hypothesised in several studies, most notably in the Rottweiler. However, there are numerous risk factors; the risk of osteosarcoma seems to increase with age, breed weight and height, and body weight. The possibility of an osteosarcoma to develop after gonadectomy should be considered as part of our individual assessments, especially in at risk breeds. 

  • Mastocytoma is the most common skin tumour in dogs; luteinizing hormone receptors are abundant in the skin. Several studies have documented an increased risk for developing mastocytoma following spaying or neutering in dogs but more evidence is needed to make strong conclusions. 

  • Lymphoma is a cancer of lymphocytes and/or lymphoid tissues. In one study in Golden Retrievers, neutered males were three times more likely to develop lymphoma than entire males. The pathogenesis of lymphoma is multifactorial but the possibility of a lymphoma to develop after gonadectomy should be considered as part of our individual assessment, especially in the breeds deemed higher risk, such as Golden Retrievers. 

  • Haemangiosarcomas are malignant tumours originating from pluripotent bone marrow. One group of researchers found expression of LH receptors in canine splenic haemangiosarcoma cell lines and, after stimulation with LH, the proliferation rate increased significantly in two of three cell lines. From this, it could be hypothesised that the increase in LH after gonadectomy might contribute to the pathogenesis of canine haemangiosarcomas in both sexes. The pathogenesis of this condition is multifactorial, and there is still no clear evidence to suggest gonadectomy is a major contributing factor yet. 

Obesity (increased risk with castration)

It is common for dogs who have been neutered to be more prone to weight pain. Surgical castration, removal of the gonads, induces obesity through two main mechanisms: increased appetite and decreased metabolic rate. Gonad removal stimulates food intake and increases indiscriminate appetite, in entire dogs, food intake suppresses the secretion of gastrointestinal hormones (cholecystokinin and glucagon), resulting in satiety (alleviation of hunger). However, within 1 week following castration, food intake increases by 20% and then persists! This can lead to obesity, and we know that a huge percentage of our pet population is overweight or obese.

Obesity is also a risk factor for a number of other health conditions in our pets - from increasing the risk of inflammatory disease and osteoarthritis. Ensuring we actively Body Condition Score (BCS) our dogs is vitally important to keep track of our pets health.

In one lifetime study, dogs who were fed an amount that resulted in them being slightly overweight had a median lifespan of nearly 2 years less than their littermates who were fed 25% less and maintained a more ideal body weight. The dogs fed less and kept more lean also had a delayed time to onset of arthritis compared to their heavier counterparts. Other studies have repeatedly shown that overweight and obese dogs and cats have a higher risk of developing other medical conditions and a lower quality of life.

This shows the huge importance of education on diet change and adjustments following gonadectomy, to ensure that dogs remain a good BCS with excellent musculature. 

Behavioural reasons for and against castration

It is not easy to fit the role of castration and behaviour into a small section, the role of gonad removal on behaviour is complex. Evidence for benefits as well as disadvantages following gonadectomy has been reported and are important to consider on a case by case basis.

Reproductive-related behaviours such as urine marking in house, mounting, and roaming all may be effectively reduced or eliminated following surgical and medical castration. Furthermore when using medical castration, such as a deslorelin releasing implant, due to their ability to suppress testosterone these implants may also be useful for altering/minimising behaviours related to testosterone. Improvements in sexually dimorphic male behaviours described as libido, hypersexuality, intermale conflict, and excessive territorial urine marking have all been described for deslorelin releasing implant.

“Testosterone related, unwanted behaviour may improve gonadectomy or hormonal treatment and inter-male aggression may improve but not all aggressive behaviours are testosterone related. The recommended age at castration depends on the reason for considering the procedure but the risk of side effects of prepubertal gonadectomy should be weighed carefully against the benefit of this measure. A so-called “castration trial” using a long-acting GnRH agonist is recommended before irreversible orchiectomy is performed.”

However, fear and aggression tend to be exacerbated. Fear of storms, fear of gunfire, fear of noises, fear related biting, timidity, separation anxiety, and submissive urination all increase significantly following spaying or neutering. Although some dogs may become less aggressive following gonadectomy,dominance aggression and owner-directed aggression occur with a significantly higher frequency in gonadectomized dogs compared with unaltered dogs.

The hippocampus and hypothalamus both play important roles in controlling behaviours, especially those pertaining to fear and aggression. Luteinizing hormone receptors are abundant in the hippocampus and hypothalamus, so this again raises the question of the role of LH, the impact castration and persistently high levels of LH when we disrupt the negative feedback mechanism. To mirror this thought, administration of supraphysiologic concentrations of LH to gonadectomized animals can induce aggression and other behavioural changes.

Medical Castration

Another option, if we have reservations that surgical castration might not be the right choice for our male dog, is to consider a form of medical castration such as a sustained release implant that contains deslorelin acetate (a GnRH superagonist), also know as a deslorelin releasing implant.

It is used in healthy, sexually mature dogs that have not been neutered to make them temporarily infertile. The implant effects can be seen at about six weeks in dogs and the effect continues for six months in the case of the 4.7 mg implant for dogs and 12 months in the case of the 9.4 mg implant for dogs, after which the dog can be re-implanted if necessary allowing this to be a non permanent option to try if we are unsure if things like behaviour will get worse or better following castration and don't want to commit to a permanent solution. 

Deslorelin acetate acts like the natural hormone gonadotropin-releasing hormone (GnRH) which controls the secretion of other hormones involved in infertility. The implant slowly releases a continuous low dose of deslorelin, this suppresses the production of follicle-stimulating hormone (FSH) and luteinising hormone (LH). As a result, in male dogs less testosterone circulates in the blood, the dog stops producing sperm and their libido is reduced. However, as we are not removing the testicles as we would in a surgical castration, the negative feedback mechanism for LH is not interrupted and there is no persistently high LH seen. Although we are still not fully sure about the connection between LH and other conditions (as aforementioned), for those owners who wish to try a non-permanent option to see if it helps with certain behaviours, or to temporarily induce infertility (e.g., If you have a young female dog you would want to have a season(s) before spaying - removing the ovaries / ovaries and uterus- but want to avoid a mis-mating) then this could be another option to your toolkit.

The bottom line

As with anything, it is important to make informed decisions, weighing up the pros and cons, and assessing each animal on an individual basis before making the decision.

For clients who are responsible pet owners (RPOs), it may be advisable to leave dogs intact, particularly in breeds prone to health detriments associated with gonadectomy.

You can do this alongside your amazing veterinary team who can help support and guide you. In most cases, when there is not a time sensitivity, or a legal or medical reason to castrate, then you always have some time to consider all the options available. As well as working with your amazing veterinary team, you may also want to work alongside other evidence based, qualified individuals such as behaviourists who can help assess your dogs behaviour and help guide the decision making. 

NB: A ‘behaviourist’ is NOT a protected title and some individuals do not work within the current evidence base and can use techniques that can make behaviour worse. See Homepage | FAB Clinicians or APBC Welcomes All - APBC for more information. 

Robyn J Lowe BSc Hons, Dip AVA (Surgery, Medicine, Anaesthesia) DipHE CVN, RVN


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