When it comes to the sexual or reproductive status of dogs, I have always been a firm believer in spaying and neutering. In a country where dogs are frequently bred irresponsibly, where there are more dogs than people to take care of them, and where ‘accidents’ happen because of irresponsible management, this has never been a question for me. But the truth is, like all of our beliefs and practices, the idea bears some scrutiny. Sterilisation is not the clear-cut issue I once believed it to be.
I discuss an article published by Chris Zink et al. in 2023, comparing spay and neuter to vasectomies and ovary-sparing spays in dogs. The article examines the behaviour and health outcomes of dogs that have undergone these procedures to help us evaluate the ethical and individual considerations that we need to consider when seeking to control breeding.
Why do we choose to spay, neuter, or pursue an alternative?
According to Trevejo et al. (2011), 64% of the US population uses surgical intervention to prevent breeding or reproduction in their dogs.
Sterilization is generally recommended for one of three reasons: population control, behavioural improvements, and perceived health benefits.
Behavioural improvements
According to Nielson et al. (1997), behavioural concerns such as roaming, mounting and urine marking in adult male dogs can all be significantly ameliorated with castration, although the fear and aggression responses are not significantly improved by castration. These results confirmed earlier findings of Hopkins et al. (1976). Some behaviours will be improved; others, not.
Health benefits
In male dogs, castration prevents the development of testicular tumours (Liao et al., 2009) while increasing the risk of prostatic carcinoma (Sorenmo et al., 2003). More recent research also reveals that early castration can cause an increased risk of orthopaedic conditions, weight gain, and cancer.
In females, a spay can prevent ovarian tumours and pyometra, and reduce the risk of mammary cancer (Schneider et al., 1969).
Hart and Hart (2021) highlight that early sterilization of either sex can lead to an increased risk of joint disease, cancer and cognitive disease, with the highest risk in large-breed dogs. These authors point out that among 35 breeds, there is a wide range in the risk of developing joint disease or cancer, as well as differences in sensitivity to the age of castration. Sterilization impacted the risk of developing joint disease when performed in dogs under two years of age.
Alternative surgical procedures
To reduce the risk of health concerns associated with sterilization while still maintaining population control, veterinarians and owners have started to investigate options such as vasectomies and ovary-sparing spays (OSS) (also known as hysterectomies). These procedures allow the retention of sex hormones within the individual which may reduce the risks of joint disease and cancer (Kutzler, 2020).
Kutzler highlights that the gonads are “not merely reproductive organs, but are necessary endocrine glands for normal metabolic, behavioural, musculoskeletal and anti-neoplastic health”.
How do these procedures compare to one another?
In a survey-based study, Zink et al. (2023) compared health and behavioural outcomes for 6018 dogs who were either intact, had received a traditional sterlisation, or had undergone a vasectomy or OSS. Spayed females were the largest part of the population, while vasectomised males made up the smallest sample collected.
Data was collected for
- 2281 spayed females
- 1672 castrated males
- 1056 intact males
- 792 intact females
- 159 OSS females, and
- 58 vasectomised males.
Within this large sample, the prevalence of health and behavioural conditions were:
- 759 dogs had orthopedic conditions
- 1127 dogs had cancer
- 192 dogs had obesity
- 320 dogs had endocrine disorders
- 194 dogs had reproductive conditions
- 1074 dogs had other health concerns
- 2035 dogs had ‘problem’ behaviours
- 484 dogs had ‘nuisance’ behaviours.
Orthopedic problems
Zinc et al. (2023) found neutered males and females to be at the highest risk of developing orthopedic conditions, while intact females and vasectomised males had the lowest risk.
An increased body size correlated with a higher risk of developing an orthopedic problem, such as elbow and hip dysplasia, cranial cruciate ligament ruptures, and patella luxations.
Cancer
Intact dogs were found to be less likely to develop cancer than dogs that had undergone a spay or neuter. Neutered males carried the greatest risk, while intact females carried the lowest risk.
Mammary cancer diagnoses were made in 3% of intact females, in 1.7% of spayed females diagnosed before the spay, and in 1.8% diagnosed after the spay. In total, 2% of OSS dogs were diagnosed with mammary cancer.
This highlights that mammary cancer remains rare, and continues to occur following a spay or OSS.
Obesity
The prevalence of obesity was less than 1% in intact males and OSS females. Obesity was not reported in vasectomised males.
In neutered males, 5% were obese, while in spayed females, 4% were obese.
These numbers were surprising, as other studies have highlighted a high prevalence of obesity among the canine population; between 22% and 40% of canines have been classed as overweight, and an additional 7% as obese (Alexander, 2006).
Bjørnvad et al. (2019) evaluated the risk of weight gain in dogs following a castration, and found that 20% of the dogs in their study were overweight or obese. Castration dramatically increased the risk of a higher BCS (body condition scoring) in males, but not in females. Females carried a high risk of obesity regardless of whether they had been spayed or were intact.
I found the data on obesity interesting, as we know that obesity hugely increases the risk of developing joint disease and other serious health conditions. The very low prevalence of obesity in Zink et al.’s study causes me to question whether data was collected accurately for this outcome measure. Owners can be notoriously lacking in their ability to distinguish between a healthy weight and obesity in their own dogs.
Endocrine conditions
Endocrine disorders were reported in less than 2% of intact females, 4% of intact males, 6% of neutered males, and 7% of spayed females.
There were no reports in the VS-OSS dogs.
Reproductive conditions
Less than 1% of neutered males presented with reproductive conditions.
In total, 7% of intact males, 4% of intact females, 7% of OSS, and 3% of spayed females presented with reproductive conditions.
In this instance, the risk of developing a reproductive condition increases the longer a dog stays intact.
Other health problems
Other health concerns included any clearly diagnosed health issue, including dental disease, heart disease, kidney disease, and disorders of the eye.
In total, 26% of spayed females, 17% of neutered males, 13% of intact males, and 8% of intact females presented with other health concerns. The likelihood of dogs experiencing other health concerns decreased the longer they remained intact.
Behavioural concerns
Zinc et al. (2023) categorised behavioural concerns into ‘problem’ behaviours and ‘nuisance’ behaviours. Problem behaviours included aggression and anxiety-related problems, while nuisance behaviours included mounting and marking.
In total, 53% of neutered males had problem behaviours, 35% of intact males had problem behaviours and 43% of OSS females had problem behaviours. Problem behaviours were more likely to occur in small-breed dogs who were sterilized at an earlier age.
In total, 13% of intact males and 11% of neutered males displayed nuisance behaviours, while 10% of VS-OSS dogs displayed nuisance behaviours.
Dogs that were sterilized at a later age were less likely to have nuisance behaviours.
If you would like to learn more about lifespan and the reason owners opt for a specific procedure, please watch our Research Refresh in the Onlinepethealth Small Animal Membership, or read the research article.
Conclusion
In conclusion, there is no clear best practice. The breed and size of the individual dog, and their health predispositions in terms of orthopedic and other health concerns, should all be considered when deciding at what age or with which procedure to achieve reproductive control, if at all. It is worth noting that early neutering in large-breed dogs has advantages for preventing reproductive problems, while exacerbating the likelihood of the dog developing joint problems or cancer. Not an easy decision to make, and other factors may come into play.
The decision of what to do and when, is therefore one that should be made in light of all the variables and risk factors of the individual, together with the needs and environment of the owner.
Vasectomies and ovary sparing spays do offer an alternative surgical approach that may reduce the risk of certain health concerns while achieving reproductive control.
References:
- Zink, K, Delgado, MM, Stella, JL. Vasectomy and ovary-sparing spay in dogs: Comparison of health and behavior outcomes with gonadectomized and sexually intact dogs. JAVMA, doi.org/10.2460/javma.22.08.0382
- Trevejo R, Yang M & Lund EM. Epidemiology of surgical castration of dogs and cats in the United States. J Am Vet Med Assoc. 2011, 238(7):898–904. doi:10.2460/javma.238.7.898
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