Updated November 29, 2020
Whether to desex or neuter your male dog is one of the most important decisions you as a pet owner will make. It’s not a simple decision; there are pros and cons plus a good amount of misinformation which utterly defy a simple answer.
If you are interested in this subject, please try to read the whole article, which may be the most important I have written. Avoid sensational headlines, take the time to absorb the detail and you will already be better than 99% of the opinion-makers online.
At the end, you will not only have the best and most up to date understanding of this subject, but you will see how easily good science can be turned into bad advice.
Worryingly, among the genuinely good articles on desexing are many who misrepresent or misread the scientific literature in support of their own ideas. Make no mistake; the consequences of the wrong decision can be disastrous.
‘Why I should not desex my dog’
This blog began innocently enough. If I had any idea how big a task it would become I might never have dared to start. The owners of a male puppy told me they had been doing their own online research and had decided not to desex. I told them my views and made sure they knew that I respected their decision, but naively I googled ‘Why I should not desex my dog’ just to see what they had been reading.
Straight away I found results which truly shocked me and made me question my own knowledge. Most of the top search results were strongly against desexing and made convincing claims of the harm being caused. Many pages referenced or linked an authoritative article titled Early Spay-Neuter Considerations for the Canine Athlete: One Veterinarian’s Opinion by Chris Zink DVM, PhD, DACVP, DACVSMR.
This article’s title suggests it is about the debate between neutering at 8 weeks and neutering at the traditional date, usually 6-7 months. However, reading the article leaves no doubt that the author is arguing against desexing at all.
The article cites high-quality scientific papers from leading journals to support its statements. I am a veterinarian quite accustomed to reading journal articles and I finished the article convinced that these statements were true. Several sleepless nights followed as I worried that I had been inadvertently giving bad advice to dog owners.
The Science Behind Desexing Dogs
There is only one way to check a scientific review author’s conclusions; by reading the original articles. The scandal of modern science is that it is not possible for 99.9% of the population to do this. Due to copyright restrictions, the full text of journal articles is only available to paid subscribers, usually university-based academics. Many people are trying to fight this, as it goes to the heart of why science is so poorly reported in the media. Here is the cause for which the internet hero Aaron Swartz lost his life. Read his story at Aaron Swartz Wikipedia article then please come back!
Luckily, a colleague with full journal access came to the rescue. He promised me that if I was having trouble sleeping, reading original scientific papers was definitely a cure for insomnia. However, I read these papers with a growing sense of astonishment. While most of Chris Zink’s statements are factually correct, there was usually another more logical interpretation or important extra information which had not been discussed.
Follow this link for a guide to doing your own research into neutering or anything else.
The Facts: Desexed vs Undesexed Dogs
I will go through each of her conclusions one by one.
That desexed dogs are more likely to be obese than undesexed dogs.
This is true (Lund et al). It is probably the most reliably observed negative association with neutering and every owner should be aware of the risk. Dogs seem to have an increased drive to eat following desexing, and simultaneously a reduced food requirement. Obesity is then associated with a wide variety of important diseases and reduced lifespan (Kealy et al).
Obesity is entirely preventable by controlled feeding. If you do not feel capable of measuring and managing your dog’s food intake and body condition, then it may be better to not neuter. However, for the majority of dog owners, this management is no different to how they have been feeding their dog all along, and all they need to do is reduce the amount fed after desexing. For more help, visit our page on helping an overweight dog lose weight.
That desexed dogs have delayed growth plate closure and are taller than undesexed dogs.
This is probably true, uncontroversial and not associated with any known problems.
That desexed dogs have a higher prevalence of cranial cruciate ligament disease (CCLD) and hip dysplasia (HD) than sexually intact dogs.
Tricky one. This is a complex discussion and there is no easy answer. There are six often-cited studies showing a link between neutering and hip dysplasia or cruciate ligament disease. I’ve asterisked (*) them in the references at the end.
The problem is always the differences in body weight. Not one of these observational studies is controlled for weight; that is, the desexed groups are heavier, and weight is a significant risk factor for CCLD and HD. We need a study that compares groups of equal body condition to answer this question adequately.
To be fair, it is very hard to design a study that can’t be faulted, and there does seem to be a trend towards HD and CCLD being more common in desexed dogs. As a consequence, these findings have influenced the best age to desex and neuter dogs. It varies with breed and sex but a quick summary is that breeds susceptible to joint problems are now being deferred to 12 months of age.
There is an abnormal angle of the stifle increasing stress on the CCL.
True, Tibial Plateau Angle is greater in desexed dogs (Duerr et al) but there’s no evidence of a significant causation to cranial cruciate ligament rupture. (Kayashi).
That desexed dogs had a higher incidence of patellar luxation.
To comment, it is enough to read the original study. “This may be in direct relation with the increased age of the neutered dogs (Table 11), as it has already been said that PL chance increases to the 1.1 fold with each year of age…Whether a change induced by neutering in the hormonal status of a dog could play any role in these mechanisms cannot be deduced from the data of the present study” Vidoni et al.
That “dogs that have been spayed or neutered at or before puberty can often be identified by their longer limbs, lighter bone structure, narrower chests and narrower skulls than intact dogs of the same breed.”
This seems to be a statement of opinion, not referenced or supported by any studies. I have the opposite opinion after literally a lifetime in and around vets that you just can’t pick the sex or desexing status without either checking the file or the undercarriage.
Desexed dogs have a higher incidence of cardiac haemangiosarcoma, prostatic cancer, transitional cell carcinoma (TCC)
This is probably true (Teske; Prymak; Ware & Hopper). However, these are relatively rare cancers and any increase if present is of minor significance.
More recently, Hart et al (2014) found a higher risk of lymphosarcoma in desexed Golden Retrievers. In contrast, Hart et al (2016) found that German Shepherds were at no greater risk of the common cancers when neutered.
Regardless of the details, the bigger picture is that overall lifespans are increased in desexed dogs. Hoffman et al studied 40,000 dogs and found that although deaths from cancer were higher,
Sterilization increased life expectancy by 13.8% in males and 26.3% in females.
Specific diseases will vary in incidence between the two groups but desexed dogs on average do better. Cancer is generally a disease of older animals, which may explain why desexed dogs get more of it.
Desexed dogs are at a higher risk of osteosarcoma
The study by Cooley et al indeed found a frightening two to fourfold increase in the incidence of bone cancer in neutered dogs. However, the same study showed the desexed dogs lived longer. Once again it is likely that extra cancer seen is at least partly due to a longer lifespan. The other studies quoted here have not managed to repeat these findings.
Desexed dogs have a higher incidence of hypothyroidism
This statement results from a selective reading of the literature. Two older studies (Milne and Hayes; Panciera) show neutering to be a risk factor for the development of hypothyroidism. However, two more recent studies (Dixon and Mooney; Dixon et al) using age-matched controls and more accurate testing found neutering had no apparent effect.
Desexed dogs have more behaviour problems
The Spain et al study cited found more noise phobias and sexual behaviour in an early desexing group but separation anxiety, roaming behaviour, urination when frightened and relinquishment by owners were less. Why was this second finding not mentioned? Regardless, the early group were treated and homed very differently, so the authors felt that the behavioural differences likely reflected management differences.
There is no question that roaming behaviour is reduced in desexed males and reasonable evidence that severe dog bites are fewer (Sacks). Click here for more on the effect of desexing on aggression.
In general, as I mentioned earlier, it is proven that desexing reduces a wide range of problem behaviour, especially biting and marking (Neilson et al; Maarschalkerweerd et al; D’onise et al). Follow this link to read about the debate over aggression in neutered female dogs.
Desexed dogs are more likely to have a vaccine reaction.
This is strange but true. Moore et al found neutered dogs were around one-third more likely to have a vaccine reaction. The overall rate was 0.38% of vaccinations.
Moving on, what about some of the more down-to-earth concerns owners may have about desexing? In contrast to the evidence-based discussion above I’ll answer these using my completely anecdotal experience and opinions. Feel free to argue.
Dogs get fat after desexing. Only if you let them.
Dogs get lazy after desexing. Only if you let them. Yes, they do seem quieter, but only when unstimulated.
Desexing male dogs takes away their spirit. My two desexed males have plenty of spirit, and so do the others I know!
Desexing changes a dog. No, no, no. Desexing helps stop a dog from changing. We recommend the operation at six months of age, such that we have done it before the unpleasant male behaviours start appearing. This way they never learn the habits and keep a more uncomplicated, puppy-like attitude. Watch the video.
Desexing reduces guarding. Behaviourists say ‘if you encourage or train guarding, you get way too much guarding’, i.e. it gets dangerous. All dogs guard instinctively and need no help.
My dog will miss his testicles. Only people do that.
There are too many anaesthetic risks with desexing. Watch my video at Male Dog Desexing made while desexing my Loki. In it I explain the surgery and anaesthetic. It’s very comforting for the worried pet owner.
Desexed dogs have less muscle. If this is true I can’t tell. I think this is an example of assuming dogs are like people.
Desexed dogs are smaller. No, in fact, they are the same, or even possibly larger.
Desexed dogs can’t breed. This is just a reminder that if you want to breed your dog, you’ll need to wait. Once breeding is over, desexing is still a good idea.
So here’s the evidence in summary form:
Why Desex Male Dogs
- Lifespan is increased (Kraft; Greer et al; Hoffman et al)
- Inter-dog Aggression,
- Sexual behaviour &
- Other problem behaviours (eg urine marking) are all reduced (Hopkins; Neilson; Maarschalkerweerd)
- Aggression to family members is reduced
- Medical conditions (prostatic enlargement, perineal hernia and testicular & perianal tumours) are eliminated.
- Cystine bladder and urethral stones are less common (Florey et al)
Why Not Desex Male Dogs
- Weight gain
- Joint diseases in immature medium and large breeds
Thanks for making it to the end. I wish people could see that vets are the least likely to do something harmful to animals. I hope I have shown how much truly misinformed material is out there and how careful we have to be. Please remember that your vet navigates the information maze daily and remains your best resource for expert advice.
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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These articles are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story!
I can provide full text copies of most of these articles on request. To view the abstract summaries, search via author and subject keywords at https://scholar.google.com.au/
Cooley, D. M., Beranek, B. C., Schlittler, D. L., Glickman, N. W., Glickman, L. T., & Waters, D. J. (2002). Endogenous gonadal hormone exposure and bone sarcoma risk. Cancer Epidemiology Biomarkers & Prevention, 11(11), 1434-1440.
Dixon, R. M., & Mooney, C. T. (1999). Evaluation of serum free thyroxine and thyrotropin concentrations in the diagnosis of canine hypothyroidism. Journal of Small Animal Practice, 40(2), 72-7
Dixon, M., Reid, S. W. J., & Mooney, C. T. (1999). Epidemiological, clinical, haematological and biochemical characteristics of canine hypothyroidism. Veterinary record, 145(17), 481-487.
D’onise, K., Hazel, S., & Caraguel, C. (2017). Mandatory desexing of dogs: one step in the right direction to reduce the risk of dog bite? A systematic review. Injury prevention, injuryprev-2016.
Duerr, F. M., Duncan, C. G., Savicky, R. S., Park, R. D., Egger, E. L., & Palmer, R. H. (2007). Risk factors for excessive tibial plateau angle in large-breed dogs with cranial cruciate ligament disease. Journal of the American Veterinary Medical Association, 231(11), 1688-1691.
*Duval, J. M., Budsberg, S. C., Flo, G. L., & Sammarco, J. L. (1999). Breed, sex, and body weight as risk factors for rupture of the cranial cruciate ligament in young dogs. Journal of the American Veterinary Medical Association, 215(6), 811-814.
Florey, J., Ewen, V., & Syme, H. (2017). Association between cystine urolithiasis and neuter status of dogs within the UK. Journal of Small Animal Practice, 58(9), 531-535.
Greer, K. A., Canterberry, S. C., & Murphy, K. E. (2007). Statistical analysis regarding the effects of height and weight on life span of the domestic dog. Research in veterinary science, 82(2), 208-214.
*Hart, B. L., Hart, L. A., Thigpen, A. P., & Willits, N. H. (2014). Long-term health effects of neutering dogs: comparison of Labrador Retrievers with Golden Retrievers. PloS one, 9(7), e102241.
*Hart, B. L., Hart, L. A., Thigpen, A. P., & Willits, N. H. (2016). Neutering of German Shepherd Dogs: associated joint disorders, cancers and urinary incontinence. Veterinary Medicine and Science.
Hoffman, J. M., Creevy, K. E., & Promislow, D. E. (2013). Reproductive capability is associated with lifespan and cause of death in companion dogs. PloS one, 8(4), e61082.
Hopkins, S. G., Schubert, T. A., & Hart, B. L. (1976). Castration of adult male dogs: effects on roaming, aggression, urine marking, and mounting. Journal of the American Veterinary Medical Association, 168(12), 1108-1110.
Kealy, R. D., Lawler, D. F., Ballam, J. M., Mantz, S. L., Biery, D. N., Greeley, E. H., … & Stowe, H. D. (2002). Effects of diet restriction on life span and age-related changes in dogs. Journal of the American Veterinary Medical Association, 220(9), 1315-1320.
Kraft, W. (1998). Geriatrics in canine and feline internal medicine. European Journal of Medical Research, 3(1-2), 31-41.
Lund, E. M., Armstrong, P. J., Kirk, C. A., & Klausner, J. S. (2005). Prevalence and risk factors for obesity in adult dogs from private US veterinary practices. Intern J Appl Res Vet Med, 3(2), 88-96.
Michell, A. R. Longevity of British breeds of dog and its relationships with sex, size, cardiovascular variables and disease. The Veterinary Record 145.22 (1999): 625-629.
Moore, G. E., Guptill, L. F., Ward, M. P., Glickman, N. W., Faunt, K. K., Lewis, H. B., & Glickman, L. T. (2005). Adverse events diagnosed within three days of vaccine administration in dogs. Journal of the American Veterinary Medical Association, 227(7), 1102-1108.
Neilson, J. C., Eckstein, R. A., & Hart, B. L. (1997). Effects of castration on problem behaviors in male dogs with reference to age and duration of behavior. J Am Vet Med Assoc 211:180–182.
Maarschalkerweerd, R. J., Endenburg, N., Kirpensteijn, J., & Knol, B. W. (1997). Influence of orchiectomy on canine behaviour. The Veterinary Record, 140(24), 617-619.
Milne K. L., Hayes H. M. (1981). Epidemiologic features of canine hypothyroidism. Cornell Vet 71, 3–14.
Panciera D. L. (1994). Hypothyroidism in dogs: 66 cases (1987–1992). J Am Vet Med Assoc 204, 761–767.
Prymak, C., McKee, L. J., Goldschmidt, M. H., & Glickman, L. T. (1988). Epidemiologic, clinical, pathologic, and prognostic characteristics of splenic hemangiosarcoma and splenic hematoma in dogs: 217 cases (1985). Journal of the American Veterinary Medical Association, 193(6), 706-712.
Reichler, I. M. (2009). Gonadectomy in cats and dogs: a review of risks and benefits. Reproduction in domestic animals, 44(s2), 29-35.
de la Riva, G. T., Hart, B. L., Farver, T. B., Oberbauer, A. M., Messam, L. L. M., Willits, N., & Hart, L. A. (2013). Neutering dogs: effects on joint disorders and cancers in golden retrievers. PloS one, 8(2), e55937.
Sacks, J. J., Lockwood, R., Hornreicht, J., & Sattin, R. W. (1996). Fatal dog attacks, 1989-1994. Pediatrics, 97(6), 891-895.
Smith, G. K., Mayhew, P. D., Kapatkin, A. S., McKelvie, P. J., Shofer, F. S., & Gregor, T. P. (2001). Evaluation of risk factors for degenerative joint disease associated with hip dysplasia in German Shepherd Dogs, Golden Retrievers, Labrador Retrievers, and Rottweilers. Journal of the American Veterinary Medical Association, 219(12), 1719-1724.
*Slauterbeck, J. R., Pankratz, K., Xu, K. T., Bozeman, S. C., & Hardy, D. M. (2004). Canine ovariohysterectomy and orchiectomy increases the prevalence of ACL injury. Clinical orthopaedics and related research, 429, 301-305.
Teske, E., Naan, E. C., Van Dijk, E. M., Van Garderen, E., & Schalken, J. A. (2002). Canine prostate carcinoma: epidemiological evidence of an increased risk in castrated dogs. Molecular and cellular endocrinology, 197(1), 251-255.
*van Hagen, M. A., Ducro, B. J., Broek, J. V. D., & Knol, B. W. (2005). Incidence, risk factors, and heritability estimates of hind limb lameness caused by hip dysplasia in a birth cohort of boxers. American journal of veterinary research, 66(2), 307-312.
Vidoni, B., Sommerfeld-Stur, I., & Eisenmenger, E. (2006). Diagnostic and genetic aspects of patellar luxation in small and miniature breed dogs in Austria. Companion Animal Practice, 16, 149.
Ware, W. A., & Hopper, D. L. (1999). Cardiac tumors in dogs: 1982–1995. Journal of Veterinary Internal Medicine, 13(2), 95-103.
*Witsberger, T. H., Villamil, J. A., Schultz, L. G., Hahn, A. W., & Cook, J. L. (2008). Prevalence of and risk factors for hip dysplasia and cranial cruciate ligament deficiency in dogs. Journal of the American Veterinary Medical Association, 232(12), 1818-1824.