Traditionally dogs have been desexed at about 6 months of age, just before they reach sexual maturity. I have been desexing our puppies at 6 weeks of age (Early Spay Neuter or ESN) since 1994

My puppies are desexed when they are still with their mother and litter group, they wake up being cuddled by a friendly human and within half an hour of the surgery they are back with their siblings, up and eating their delayed breakfast. Baby puppies are remarkably resilient, the surgery is quick, simple and with appropriate pain relief it is remarkably stress free.

Compare this with the stress of being taken to a strange place at 4-6 month of age, left among strangers and submitted to a major operation, then having to wear a weird plastic collar for 10 days. It is not surprising that most dogs hate going to the vet ever afterwards.

There are good reasons for my decision to desex my puppies early:

Desexing female dogs before puberty almost completely prevents mammary cancer while every oestrus cycle hugely increases that risk. Female dogs spayed before any oestrous cycles had approximately 0.5% of the mammary cancer risk; those that had only 1 oestrous cycle had 8%, and animals that had 2 or more oestrous cycles before neutering, 26%.1

Desexed male dogs are less likely to scent mark, roam, fight or bite children 9-13.

Because I am a vet I can perform the operation myself, saving new owners hundreds of dollars and giving me the peace of mind from the certainty that my crossbred dogs, are not going to be used for random breeding.

When I started, the research showed that, while there were some conditions which may be affected by desexing prior to 12 months, there was no evidence that the age of desexing prior to puberty was an issue1. Since then I have carried out several surveys of my dogs and I believe that the results support this view – in my medium sized crossbred dogs. The RSPCA still practices and supports ESN and you can read more about this on their website

There has been a great deal of research more recently which has led many veterinarians to recommend that puppies, particularly females, should not be desexed before 4 months of age. The concerns regarding ESN relate to urogenital tract problems, obesity, behaviour problems, joint issues and cancer incidence.

UROGENITAL TRACT PROBLEMS
Urinary Incontinence (urinary sphincter mechanism incompetence – USMI)
Desexing female dogs does create a risk that they will develop USMI – regardless of the age at which they are desexed. It has been reported to affect between 3.0% and 20.0% of all female spayed dogs2.
This problem is common particularly in some larger breeds. Urinary incontinence affects just over 3% of bitches overall but affects more than 15% of bitches in high-risk breeds3. USMI causes in passive leaking of urine usually while the dogs are asleep. it is usually responsive to hormone supplementation.

The big debate has been whether dogs desexed before puberty (6-9 months) may be more prone to developing USMI and whether ESN may further increase this risk.
The results are contradictory. One study has shown that USMI is more common in ESN puppies3 and has led to the recommendation that females shouldn’t be desexed before 4 months of age. However another4 showed that ESN puppies are less likely to develop urinary incontinence than females spayed later.

A systematic review of all the research, carried out in 2011 found:

There is only weak evidence that neutering bitches, particularly before the age of three months, increases the risk of urinary incontinence.

And concluded that:

The evidence is not consistent nor strong enough to make firm recommendations on the effect of neutering or age at neutering on the risk of urinary incontinence5.

I have carried out a number of surveys on my dogs. In 2011 I found that 1.6% of 522 dogs reported chronic urinary problems, which was encouraging news but not very specific. In a more detailed survey in 2016 I found that 17 of 434 dogs over 4 years old (3.9%) had urinary incontinence. When I looked more closely at this figure I found that of the 259 dogs that were under 14 years old only four were incontinent and one of the dogs was a male. That makes the incidence 1.16% in all but geriatric female dogs.

What is much more important than age of desexing is the breed, size and level of obesity of the dog and I believe our results are consistent with a 2017 paper2 which concluded
Age at neutering of bitches <25 kg may not impact continence. Heavier dogs have increased risk of USMI, and onset occurs within a few years of neuter.

Recessed vulva
This problem has also been identified as a reason for delaying desexing surgery. Dogs desexed prior to surgery have immature “external genitalia” but there is no evidence that the small size of the penis or vulva cause health problems.

Recessed vulva is a conformational problem related to breed and so has a genetic basis. Females with recessed vulva are prone to vaginitis, skin fold dermatitis and urinary tract infections. They spend a lot of time licking themselves which is worrying and annoying

Early desexing doesn’t cause a recessed vulva, but going through normal heat cycles, so that the vulva matures, may correct the vaginitis and dermatitis if the bitch is not spayed before puberty. There are reports that recessed vulva is more common in ESN puppies.

Our 2016 survey identified one dog with a recessed vulva. We have established that early surgery at the time of spaying is simple and effective in correcting this problem so we now check carefully and perform corrective surgery in the occasional puppy that appears overly recessed.

OBESITY
There is no doubt that desexed dogs are more likely to be obese but the research shows that Gonadectomized dogs had a greater risk of being overweight than did sexually intact dogs, but this risk was not influenced by age at gonadectomy7.

And there is at least one study which found that ESN dogs were less likely to become obese than dogs desexed later in life4 it appears to be generally accepted now that obesity is not an issue for ESN puppies
Our 2016 survey found that, based on owner reporting, about 5% of our dogs are overweight.

BEHAVIOUR
One of the main reasons I have always practiced ESN was that dog bites (particularly to children) are largely caused by entire male dogs 8,9,10. Dog bites/attacks have been attributed heavily to male dogs, accounting for 70% of bites in some studies10and over half the dogs reported to display aggressive behaviour toward humans are reproductively intact males 11,12
and again

failure to neuter a dog and selection of male dogs and certain breeds ………..may increase the risk of their dog biting a non household member, who often may be a child13.

These days the majority of pet dogs in Australia are desexed and now studies are showing that there is an increase in some undesirable behaviours in desexed dogs which have been related to the age of desexing. Most undesirable behaviours identified in ESN dogs relate to anxiety and fear based aggression, there were also a few behaviours that were more desirable including less separation anxiety and house soiling.

The problem with many of these studies is that ESN dogs often come from animal shelters, because ESN is not commonly practiced elsewhere, and so early trauma and inadequate socialisation, which have been shown to adversely affect adult behaviour 14,15,may be implicated in these results.

One of these large studies looking at the effect of the time since desexing and age at desexing stated. We cannot determine a cause-effect relationship between gonadectomy and behaviour, as there are multiple confounding factors including but not limited to age, breed, general health condition, diet, lifestyle, socialisation and household dynamics and the importance of learning and genetic influences cannot be overstated16

We aim to only breed from dogs with good temperament and have a strict socialisation program which includes early neural stimulation17 for all our puppies. In our 2016 survey we found that 83.4% of owners were very satisfied with their dog’s behaviour and 85.3% were happy with their dogs “trainability”. Since then we have modified and intensified our socialisation program as a result of a more recent controlled study18. 100% satisfaction may never be an achievable goal but it is an excellent target.

JOINT PROBLEMS
The conditions which are of most concern are Cranial Cruciate Ligament injury (CCL- the same condition as ACL in humans) and Hip Dysplasia (HD) and most research focuses on whether or not desexing, or the age of desexing increases, the risk of these conditions. The answer seems to be yes and sometimes.

Two recent studies have found that desexed dogs under 20kg, whether purebred23 or crossbred24, do not have a significantly increased risk of joint disorders compared with entire dogs. And these studies have suggested that the age of desexing for small and medium sized dogs should be a matter of choice.

However other studies have shown that the prevalence of Cranial Cruciate Ligament (CCL) injury does increase in desexed dogs and was reported in a 2004 study to be 3.48% of all dogs with a 2.25% in entire dogs and a 4.71% incidence in desexed dogs19.

Hip Dysplasia is not as clearly associated with desexing. In one study, of over 90,000 hospital records, desexing was not associated with an increased risk of Hip Dysplasia20 however studies in Golden retrievers21 and German Shepherds22 have shown an increased incidence of hip dysplasia in male dogs desexed before 12 months.

The apparent contradiction seems to arise when all breeds and sizes of dogs are aggregated and the varying responses for different breeds and sizes can’t be statistically identified in the combined figures.

The majority of dogs we breed are under 20 kg. Our male Groodles and some male Minigroodles are over 20 kg as adults but our females rarely reach 20kg. In the light of the findings we have decided that if people request this then we will sell our male Groodles entire, on the understanding that they will not be desexed until they reach 12 months of age

CANCER
It was a 1969 study2 which first clearly showed that desexing before puberty is protective against mammary cancer. In Norway, where female dogs are very rarely desexed:
The crude incidence of malignant mammary tumours (number affected divided by the total population at any one time) in female dogs of any breed was 53.3%26 and the incidence (or risk) of contracting mammary cancer for various breeds in Norway ranged from 0.38- 3.54%. This is the main reason why desexing females before puberty has become routine in Australia.

Before we consider the downside of desexing with regards to incidence of other cancers it is important to remember that desexed dogs consistently live longer than entire dogs27
40,000 sterilized and reproductively intact domestic dogs, Canis lupus familiaris.

We found that sterilization was strongly associated with an increase in lifespan, and while it decreased risk of death from some causes, such as infectious disease, it actually increased risk of death from others, such as cancer.
And
Sterilization increased life expectancy by 13.8% in males and 26.3% in females.
It is therefore possible that desexed dogs get cancer because they live longer (just as people do as life expectancy has increased)

So to the down side of cancer and desexing: Desexed dogs do suffer from an increased number of cancers such as hemangiosarcoma and lymphoid neoplasia.
This occurs across all breeds but is particularly a problem for Golden Retrievers28. Goldens are beautiful dogs (if they didn’t shed so much hair no-one would get a Groodle) but they are horribly prone to cancer. As many as 65% of Golden Retrievers die of cancer and desexing increases the risk of cancer in female Golden Retrievers 28,29 which has led one large study to recommend that female Golden Retrievers should not be desexed at all 24

BUT desexed female golden retrievers live longer than entire females! Confused? So am I – and I would be very concerned if I was a Golden Retriever breeder. And what is the recommended solution for Golden Retriever breeders?
The solution is to bring in new blood from gene pools with much lower risk of cancer30 Like Poodles or Cavaliers for example?

REFERENCES
1. Salmeri KR, Bloomberg MS, Scruggs SL et al. Gonadectomy in immature dogs: effects on skeletal, physical, and behavioral development. J Am Vet Med Assoc 1991;198:1193–1203.
2. Factors Influencing Canine Mammary Cancer Development and Postsurgical Survival
Robert Schneider, C. Richard Dorn, D. O. N. Taylor. Journal of the National Cancer Institute, Volume 43, Issue 6, December 1969, Pages 1249–1261, https://doi.org/10.1093/jnci/43.6.1249
3. Urethral Sphincter Mechanism Incompetence in 163 Neutered Female Dogs: Diagnosis, Treatment, and Relationship of Weight and Age at Neuter to Development of Disease
J.K. Byron, K.H. Taylor, G.S. Phillips, and M.S. Stahl. Vet Intern Med 2017;31:442–448
4. What is the optimal age for desexing?
• Xavier Schneider BIT BLM (Hons) BVSc (Hons) Proceedings of the ASAV, SCGV and AVBIG 2018 Conference, Melbourne
5. Long-term risks and benefits of early-age gonadectomy in dogs.
Spain CV, Scarlett JM, Houpt KA.J Am Vet Med Assoc. 2004 Feb 1;224(3):380-7.
6. The association between acquired urinary sphincter mechanism incompetence in bitches and early spaying: a case-control study
B de Bleser 1, D C Brodbelt, N G Gregory, T A Martinez. The Veterinary Journal
Volume 187, Issue 1, January 2011, Pages 42-47
7. The effect of neutering on the risk of urinary incontinence in bitches – a systematic review Beauvais, J. M. Cardwell and D. C. Brodbelt Journal of Small Animal Practice Vol 53  April 2012
8. Effect of age at gonadectomy on the probability of dogs becoming overweight
Sandra L. Lefebvre, DVM, PhD; Mingyin Yang, BVMS, MS; Mansen Wang, PhD;
Denise A. Elliott, BVSc, PhD, DACVIM, DACVN; Preston R. Buff, PhD; Elizabeth M. Lund, DVM, MPH, PhD
9. Owner complaints about canine behavior. Beaver BV (1994) Journal of the American Veterinary Medical Association 204:1953 1955.
10. Dominance aggression of dogs towards people: behavior profile and response to treatment. Line S, Voith VL (1986) Applied Animal Behaviour Science 16:77±83.
11. The ecology of dog bite. Beck AM, Loring H, Lockwood R (1975) Public Health Reports 90, 262±267.
12. Clinical classification of canine aggression. Beaver BV. Appl Anim Ethol.(1983) 10:35–43.
13. Canine Aggression: Dog Bites To People. Wright J. In: Readings in Companion Animal Behavior. Trenton, NJ: Veterinary Learning Systems (1996). p. 240–6.
14. Which dogs bite? A case-control study of risk factors. Gershman KA, Sacks JJ, Wright JC. Pediatrics. 1994;93(6):913–7
15. Serpell JA, Duffy DL. Aspects of juvenile and adolescent environment predict aggression and fear in 12-month-old guide dogs. Front Vet Sci. (2016) 3:49. doi: 10.3389/fvets.2016.00049
16. Puppy parties and beyond: the role of early age socialization practices on adult dog behaviour, Tiffani J Howell, Tammie King, Pauleen C Bennett. Veterinary Medicine: Research and Reports. 29 April 2015.
17. Behavioural risks in female dogs with minimal lifetime exposure to gonadal hormones
Melissa StarlingI, Anne Fawcett1, Bethany Wilson1, James Serpell, Paul McGreevy.
PLOS ONE | https://doi.org/10.1371/journal.pone.0223709 December 5, 2019
18. Periods of Early Development and the Effects of Stimulation and Social Experiences in the Canine. Carmen L. Battaglia, PhD, Journal of Veterinary Behavior: Clinical Applications and Research. Volume 4, Issue 5, September–October 2009, Pages 203–210
19. Improving puppy behavior using a new standardized socialization program
Helen Vaterlaws-Whiteside, Amandine Hartmann, Applied Animal Behaviour Science 197 (2017) 55–61
20. Canine Ovariohysterectomy and Orchiectomy Increases the Prevalence of ACL Injury, J. R. Slauterbeck, MD; K. Pankratz, MD; K. T. Xu, PhD; S. C. Bozeman, DVM‡ and D. M. Hardy, PhD Clinical Orthopaedics and Related Research · January 2005.
21. Correlation of neuter status and expression of heritable disorders. Belanger et al. Canine Genetics and Epidemiology (2017) 4:6 DOI 10.1186/s40575-017-0044-6
22. Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers Gretel Torres de la Riva,, Benjamin L. Hart , Thomas B. Farver, Anita M. Oberbauer, Locksley L. McV. Messam, Neil Willits, Lynette A. Hart February 13, 2013 https://doi.org/10.1371/journal.pone.0055937
23. Neutering of German shepherd dogs: associated joint disorders, cancers and urinary incontinence. Hart BL, Hart LA, Thigpen AP, Willits NH. Vet Med Sci. 2016;2:191–9.
24. Assisting Decision-Making on Age of Neutering for 35 Breeds of Dogs: Associated Joint Disorders, Cancers, and Urinary Incontinence. 07 July 2020. Benjamin L. Hart , Lynette A. Hart, Abigail P. Thigpen and Neil H. Willits Vet. Sci. 7:388. doi: 10.3389/fvets.2020.00388
25. Assisting Decision-Making on Age of Neutering for Mixed Breed Dogs of Five Weight Categories: Associated Joint Disorders and Cancers. Benjamin L. Hart , Lynette A. Hart, Abigail P. Thigpen and Neil H. Willits. Frontiers in Veterinary Science | frontiersin.org uly 2020 | Volume 7 | Article 472
26. Population-based incidence of mammary tumours in some dog breeds. J Reprod Fertil Suppl. 2001;57:439-43.
27. Reproductive Capability Is Associated with Lifespan and Cause of Death in Companion Dogs. Jessica M. Hoffman1, Kate E. Creevy2*, Daniel E.L. Promislow1* https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0055937
28. Association of cancer-related mortality, age and gonadectomy in golden retriever dogs at a veterinary academic center. Kent MS, Burton JH, Dank G, Bannasch DL, Rebhun RB. (1989–2016). PLOS ONE. Public Library of Science; 2018;13: e0192578. pmid:29408871
29. Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers. Gretel Torres de la Riva,, Benjamin L. Hart , Thomas B. Farver, Anita M. Oberbauer, Locksley L. McV. Messam, Neil Willits, Lynette A. Hart February 13, 2013, https://doi.org/10.1371/journal.pone.0055937
30. Do Spayed and Neutered Dogs Get Cancer More Often? Jessica Perry Hekman, DVM, MS. https://blogs.scientificamerican.com/dog-spies/do-spayed-and-neutered-dogs-get-cancer-more-often/