Should we castrate? It is clear that the question of surgical neutering is a much debated and emotive issue (Reichler, 2009; Warnes, 2018): a Google search entitled ‘we should castrate dogs’ returned 5 680 000 results, whereas a search entitled ‘we should NOT castrate dogs’ returned 23 500 000. Almost all rescue centre websites, and all veterinary and public body websites that the author visited were in favour of castration (e.g. dogstrust.org.uk ‘why neuter your dog’; PDSA.org.uk ‘neutering advice’; battersea.org.uk ‘dog neutering’) listing population control and behavioural benefits as the main reasons for encouraging it.
2015 figures from Dogs Trust suggested that around 50 000 dogs are abandoned each year (https://www.bbc.co.uk/news/uk-34413490). That number is likely to have increased significantly over the past year because of the number of dogs bought during lockdown and the cost of living increases. It is clear that population control is required, although it is impossible to determine what proportion of the problem is compounded by irresponsible breeding.
The British Veterinary Association (BVA) advises that the benefits of castration outweigh welfare considerations. The BVA Policy statement on castration in male dogs (www.bva.co.uk/News-campaigns-and-policy/policy/Companion…/Neutering/) says that ‘Castration rarely produces undesirable changes in temperament. Any weight change can be controlled by management of the diet. Veterinary advice should always be sought on each individual case.’
The Royal Veterinary College (RVC) website states: ‘We recommend that both male and female dogs are neutered (castrated for males and spayed for females) from 4 months of age on health grounds. We base this recommendation on the best scientific evidence available.’ (https://www.rvc.ac.uk/small-animal-vet/general-practice/practice-services/routine-pet-healthcare/neutering-spaying-pet/dog-puppyneutering).
Approximately 54% of dogs in the UK are castrated, with the average recommended age being 7.4 months (Diesel et al, 2010). There is clearly a strong drive for owners to get their dogs castrated, and most sources the author examined list advantages of castration as follows:
- Population control
- Limits straying — particularly in response to bitches in season
- Reduces unwanted sexual behaviour towards bitches, people and inanimate objects
- Eliminates risk of testicular cancer — second most common tumour in male dogs
- Protects against prostatic disease, including inflammation and benign prostatic hypertrophy
- Prevention or treatment of medical conditions such as perineal hernias and perianal adenomas
- Reduces certain types of aggression
- Increases longevity.
When disadvantageous consequences of castration are mentioned, these include:
- Worsening of certain types of behaviour
- Obesity
- Increased risk of certain forms of cancer, such as osteosarcoma, mast cell tumour and lymphoma
- Increased risk of hip dysplasia
- Hypothyroidism
- Surgery and anaesthesia for the procedure carries a risk
- Additionally, many owners worry that castration will lead to personality changes, such as ‘dullness’, or changes in the hair coat.
Although there are many thousands of published articles on this subject, many papers show poor or even conflicting evidence. It can thus be difficult to sort the chaff from the wheat. The author has tried to present the relative arguments and evidence as concisely and clearly as possible. The interested reader may want to also refer to the companion article ‘Spaying bitches: why? when? how? (Hoad, 2018).
Advantages of castration
Longevity
There is fairly good evidence to suggest that castration, like spaying, increases the expected lifespan of a dog (Hoffman et al, 2013; Howe, 2015), although this may depend on dog breed and size (O'Neill et al, 2013). There may be various reasons for this, although chromosomal change has been suggested as a reason (Perls et al, 2002). Interestingly, castrated humans (culturally known as Eunuchs), have also been shown to have increased longevity (Min et al, 2012).
Testicular tumours
Testicular tumours are one of the most common tumours in dogs (Gazin et al, 2022), suggested in one study to be approximately 1700 per 100 000 dog-years (Baioni et al, 2017). The main testicular neoplasms are interstitial cell (Leydig) tumours, Sertoli cell tumours and seminomas (Figure 1). Cryptorchid dogs are prone to a several-times increased likelihood of all types of testicular tumour (both in the descended and non-descended testicle) as apposed to noncryptorchid dogs (Figure 2). Although the rate of metastasis is low, testicular tumours can cause discomfort, swelling and in some cases (especially sertoli cell tumours) feminisation syndrome. This can results in gynecomastia, penile atrophy, galactorrhea (milk production) and hair loss. Other changes include myelotoxicosis (bone marrow suppression), which can lead to anaemia, neutropenia and thrombocytopenia, and may be fatal, even after castration.
The overall rate of recovery following castration is excellent (in the absence of metastatic disease) and, of course, juvenile castration will prevent testicular neoplasia.
Prostatic disease
Benign prostatic hyperplasia (BPH) affects most male dogs over 5 years of age (Berry et al, 1986; Dhivya et al, 2012). Clinical signs may be absent or mild, or dogs may present with dyschezia or ribbon-like faeces, or urethral bleeding. Castration will prevent or completely reverse BPH.
Prostatic cystic hyperplasia, prostatitis and abscessation are all treated successfully by castration, coupled with appropriate antibiotic and anti-inflammatory treatment. All are extremely unlikely to occur in castrated individuals.
Perineal hernias
Castration appears to confer protection against perineal hernias in dogs (Hayes and Wilson, 1977), although the mechanism is uncertain.
Perianal adenomas
Otherwise termed hepatic gland tumours, these common benign tumours are predominantly sex-hormone dependent and are usually treated successfully by castration (and, indeed, prevented by castration): often without the need to resect the tumour itself.
Behavioural benefits
Although it is widely recognised and accepted that certain forms of aggression, sexual behaviour, straying and urine marking are all reduced with castration, it is difficult to find good data substantiating this (Maarschalkerweerd et al, 1997; D'Onise et al, 2017). There is a growing acceptance that castration alone is insufficient to treat problems such as aggression in dogs but should be performed in conjunction with good behavioural assessment, advice and training.
Population control
As already mentioned, responsible breeding should be the aim of veterinary advice to dog owners; however, there is little doubt that castration is an effective form of population control (Figure 3). Rescue centres and canine charities have all reported an increase in the numbers of unwanted dogs (BBC, 2022; Nature Wolrd News, 2022): this places a massive strain on those charities and inevitably leads to welfare issues. In the UK there is not a substantial stray dog problem, but elsewhere in the world the prevalence of stray dogs increases the risk of spread of disease, including rabies, dog bites to people, and attacks on livestock. Castration forms an essential method of population control in these areas (see later).
Disadvantages of castration
Prostatic disease
Prostatic neoplasia, although uncommon in dogs, is invariably fatal (White, 2012). Castration has not been shown to have any benefit in reducing the incidence of prostatic neoplasia: White (2012) notes that there may in fact be an increased incidence in castrated dogs, with more frequent development of pulmonary metastasis.
Behaviour
As mentioned above, information regarding the links between behaviour and castration is difficult to interpret reliably: there are many conflicting reports (Zink et al, 2014; Kaufmann et al, 2017; McGreevey et al, 2018). McGreevey et al (2018), in particular, highlight the potential detrimental behaviour changes in prepubescent castrated dogs (such as some forms of aggression). They make the contention that this may complicate the benefits of juvenile castration in population control measures. Behavioural risks in male dogs with minimal lifetime exposure to gonadal hormones may complicate population-control benefits of desexing (although their conclusion is that the benefits probably still outweigh the risks).
Obesity
Neutering of either sex of dog has long been associated with obesity, and dietary advice is generally given at the time of neutering to help counter this. Various studies have provided evidence for this (Martin et al, 2006; Lefebvre et al, 2013). There are likely multifactorial bases for the increase in weight gain, although the hormonal causes may also represent an increased risk of diabetes in castrated dogs (Marmor et al, 1982).
Hormonal effects
Some or all of the deleterious effects of castration may be mediated through the lack of negative feedback on the hypothalamus, causing chronic supraphysiologic elevation of luteinising hormone (LH) (Kutzler, 2020). Kutzler proposed that the chronically increased levels of LH may be responsible for other diseases seen more commonly in castrated dogs (urinary calculi, diabetes and various cancers, such as splenic haemangiosarcoma, lymphosarcoma, osteosarcoma, mast cell tumour). Castration has also been implicated in an increased risk of hypothyroidism (Dixon and Mooney, 1999).
Cancer
Possibly linked to the delay in epiphyseal closure (growth plate closure) seen with juvenile castration, there is an increased risk of osteosarcoma in some breeds of as much as four times higher than entire dogs (Ru et al, 1998; Cooley et al, 2002; de la Riva et al, 2013; Hart et al, 2016). Similarly, some studies have shown an increased risk of other cancers such as lymphosarcoma (Torres de la Riva et al, 2013; Zink et al, 2014) and mast cell tumours (White et al, 2011).
Orthopaedic effects
Cranial cruciate disease (Torres de la Riva et al, 2013) and hip dysplasia (van Hagen, 2005) have both been shown to have an increased incidence in castrated dogs, although it is widely recognised that these conditions have multiple causes and risk factors, so it is difficult to adequately assess the absolute role of neutering with these diseases. In fact, that can be said of most of the ‘side effects’ of castration, which makes it very difficult to give specific and concise advice to owners.
Ill effects are likely to be breed specific and multifactorial: genetic and epigenetic factors, nutrition, exercise, juvenile trauma etc. will all play a part.
Risks of castration surgery
The risks of castration surgery are generally low, as they are elective procedures performed, in general, on young, healthy patients. However, general anaesthetic always carries a risk, as does any surgical procedure. Seroma or haematoma is not infrequently seen after castration, and may result in some degree of postoperative morbidity. Cryptorchid surgery carries an increased risk of surgical trauma (Figure 4), even when minimally invasive ‘keyhole’ procedures are performed (Khan et al, 2018).
Alternatives to castration
A minimally invasive ‘field surgical’ technique for castration has been proposed. Pin hole castration involves utilising a very small incision to ligate and cut the ductus deferens and testicular vasculature, leading to atrophy of the testicle (Okwee-Acai et al, 2013). Although this may be an attractive procedure for resource-poor countries, it seems unlikely to be utilised much in the UK. In any case, longterm advantages and disadvantages for this procedure will be as for routine castration.
‘Chemical’ castration
Various hormone analogues and antagonists are available as alternatives to surgical castration. Full discussion of these drugs is beyond the scope of this article, but briefly they are Tardak (delmadinone acetate, Zoetis, UK) and Suprelorin (deslorin acetate, Virbac, UK).
Tardak
Tardak is administered by intramuscular or subcutaneous injection. Indications are treatment of hypersexuality (including vagrancy); relief of prostatic hypertrophy, whether benign, carcinomatous, or from chronic inflammatory processes (only when combined with antibiotics and steroids). It is also used in the treatment of circumanal tumours, and for certain forms of aggressiveness, nervousness, epileptiform seizures and corticosteroid-resistant pruritus. The standard drug for many years, reliability was always questioned (Beceriklisoy et al, 2010); however, efficacy seems not dissimilar to the more modern drugs for treating BPH (Albouy et al, 2008). Although it is still used, the newer drugs have, by and large, replaced it.
Suprelorin
Suprelorin is a subcutaneous sustained release implant containing deslorin acetate (a gonadotrophin-releasing hormone super agonist). Effects can be seen in about 6 weeks and can last for 6–12 months, depending on the implant size (4.7 and 9.4 mg; Figure 5). The effects are similar to surgical castration, in terms of prostatic shrinkage, infertility and behavioural changes. The testes often shrink markedly and may remain smaller for several months beyond the stated duration of the implant. Administration can be repeated, and it has no effect on long-term fertility. It is often now used to determine whether castration would produce the desired effect.
Ypozane
Ypozane (osaterone acetate, Virbac, UK) is an oral treatment containing osaterone acetate. Its licensed indication is as a treatment for BPH. It is an androgen receptor antagonist that blocks the action of testosterone on prostatic tissue. It is given once daily for 7 days, and effects last for at least 5 months. It has no effect on long-term fertility.
Optimum age for castration
It is difficult to provide standard, evidence-based advice on the optimum age for castration (and indeed whether castration should even be performed), given the preceding discussion. From a population control aspect, it would be sensible for juvenile castration to be considered in a rescue centre: however, for private owners the decision is a little more complicated. Every case should be considered on its own merits. Bearing in mind the lack of evidence for improved aggression, in particular, following castration, it may be worth considering treatment with suprelorin as a ‘trial’ prior to castration: behavioural advice from a suitably qualified and experienced behaviourist is essential to improve outcome.
The information presented here is by no means exhaustive: there are many other articles and papers published to show potential disadvantages of castration and the potential for increased disease as well as papers claiming potential advantages and reductions in disease. This article is intended to provide an overview of the pros and cons of castration. What is clear from the literature is that there is no single advantage or disadvantage that may outweigh the others, although population control is the most robust argument for widespread castration. It is likely that, as research continues, more breed specific advice with regard to castration may be available, as there seem to be breed differences in the response to castration. As many of the detrimental effects of castration may be as a result of early castration (i.e. prior to skeletal maturity), it may be prudent to recommend delaying castration beyond this age, particularly in larger breeds. Whereas it is undeniable that castration will prevent breeding, testicular tumours and BPH, there is also the risk that certain diseases such as lymphoma, cruciate disease and osteosarcoma may be more like to occur. When castration is considered for behavioural problems, it would certainly be more appropriate to advise consultation and assessment by an accredited behaviourist in the first instance. It may be that ‘chemical castration’ is utilised as part of the behavioural modification programme, rather than surgical castration: this would thus be reversible should castration not produce the desired effect.
Conclusion
It is vital that owners are aware of potential pros and cons of any surgical technique, and castration is no exception. Given the inconsistencies between perceived or historic knowledge about castration, and the growing evidence base for deleterious effects of castration, providing all the information can be challenging. Knowing the reasons a client is considering castration (e.g. population control, behaviour, health risks) may help drive the discussion forward to tailor advice for a particular case.
KEY POINTS
- Dog castration is frequently performed on sexually and skeletally immature dogs with little evidence-based supporting advice given to clients.
- The main advantage of castration appears to be population control, although there are other benefits (such as reduction in prostate hyperplasia, eradication of testicular tumours and reduction in scent marking and straying.
- Castration, particularly of immature dogs, may increase the risk of development of diseases such as osteosarcomas and cranial cruciate disease, and may worsen certain types of aggression.
- There are numerous reports of adverse effects of castration in the literature, although these are often restricted to specific breeds. It can be difficult to relate many of these reports to the wider population of dog.
- When advising a client on the pros and cons of castration, it is important to bear in mind that there is no single answer, and that each patient must be weighed up on its own merits, and the wishes and concerns of the owner.