An evidence-based guide to spaying or neutering timing. Weigh breed-specific joint-disease, cancer, and incontinence risks using the latest UC Davis breed-cohort studies.

For decades, the standard recommendation in veterinary medicine was to spay or neuter dogs at approximately six months of age. This rule was designed primarily as a population-control measure, simplified to be easily understood by the public and implemented uniformly across shelters and private practices. However, over the past decade, a growing body of peer-reviewed clinical evidence has demonstrated that a one-size-fits-all approach to gonadectomy (spaying or neutering) is outdated and potentially harmful.

The decision of when—or if—to spay or neuter a dog should be breed-specific, sex-specific, and risk-weighted. Removing the gonads (testes or ovaries) eliminates sex hormones (testosterone, estrogen, and progesterone) that are critical not only for reproduction but also for musculoskeletal development, growth plate closure, immune function, and endocrine balance.

By analyzing the latest clinical data, particularly the landmark breed-by-breed studies from the University of California, Davis (UC Davis), veterinary teams and pet owners can navigate the complex tradeoffs between orthopedic disease, oncological risks, urinary incontinence, and reproductive infections.

Why is the old 'six months' rule no longer the default?

The six-month default is increasingly obsolete because it fails to account for the role of gonadal hormones in skeletal development. In dogs, estrogen and testosterone are the primary chemical signals that tell long bones (such as the femur and tibia) when to stop growing. These hormones trigger the closure of the growth plates (epiphyseal plates) during adolescence.

Estrogen, in particular, plays a critical role in skeletal maturation in both male and female dogs. In males, circulating testosterone is locally aromatized into estrogen within the bone tissue to stimulate growth plate closure. When a puppy is spayed or neutered before physical maturity, the lack of gonadal hormones delays the closure of these growth plates. As a result, the long bones continue to grow longer than they normally would. This alters the dog's adult skeletal conformation, resulting in longer limbs, a higher center of gravity, and, crucially, abnormal joint angles.

This skeletal lengthening is particularly problematic for large and giant breeds. It increases structural stress on the joints, predisposing the dog to developmental orthopedic diseases. The two most common complications are:

hip dysplasia in dogs: A malformation of the coxofemoral joint where the femoral head does not fit snugly into the acetabulum. Early alteration disrupts the balanced growth of the bone and supporting soft tissues, increasing joint laxity.
CCL tear in dogs: Cranial cruciate ligament rupture, the canine equivalent of an ACL tear. The altered tibial plateau angle resulting from delayed growth plate closure increases shear forces on the CCL, making it highly susceptible to non-contact tears.

The Biological Mechanism: Receptors and Collagen Synthesis

Estrogen receptors (ER-alpha and ER-beta) are present throughout the musculoskeletal system, including on chondrocytes within the growth plates, osteoblasts in bone, and fibroblasts in ligaments and tendons. Testosterone also binds directly to androgen receptors on these cells. These hormones regulate the synthesis of extracellular matrix proteins, particularly collagen.

When gonadectomy is performed early, the sudden loss of estrogen and testosterone leads to:

Altered Collagen Cross-linking: Estrogen is essential for regulating collagen fiber diameter and cross-linking in the cranial cruciate ligament. Without it, the ligament's tensile strength is reduced, leaving it more vulnerable to mechanical failure under normal loads.
Growth Plate Asynchrony: Because different growth plates close at different times (e.g., the distal radial plate closes around 8–10 months, while the tibial plateau closes around 10–12 months), early alteration causes asynchronous growth. This leads to a mismatch in limb length and joint alignment, altering the mechanical axis of the hindlimbs.

Beyond skeletal maturation, sex hormones play a complex role in regulating the immune system. Estrogen and testosterone receptors are present on a wide variety of immune cells, including T-lymphocytes, B-lymphocytes, and macrophages. These hormones help modulate cell-mediated immunity and immune surveillance. Early gonadectomy has been epidemiologically linked to an increased risk of certain systemic cancers, such as lymphoma, mast cell tumors, hemangiosarcoma, and osteosarcoma. In female dogs, early spaying also removes the estrogen support needed for urethral sphincter tone, leading to urethral sphincter mechanism incompetence (USMI)—commonly known as spay-induced urinary incontinence.

Because different breeds grow at vastly different rates—a Chihuahua may reach full skeletal maturity by 8 months, whereas a Great Dane may continue growing until 24 months—a single age-based guideline is biologically unsound.

Historical Context: How Six Months Became the Standard

To understand why the six-month recommendation has persisted so tenaciously, it is necessary to examine its origins. In the 1970s and 1980s, animal shelters in the United States faced an overwhelming pet overpopulation crisis, resulting in the euthanasia of millions of healthy cats and dogs annually.

To address this, shelter medicine pioneers and major animal welfare organizations launched aggressive public education campaigns promoting spaying and neutering. The age of six months was selected not because of developmental or physiological evidence, but because it represented the earliest age at which surgical anesthesia was considered reasonably safe with the veterinary protocols of the era, while ensuring the procedure occurred before the animal could produce an unplanned first litter.

Private practices quickly adopted the six-month guideline, and over the next four decades, it became an unexamined default. While highly successful as a public health initiative to reduce shelter admissions, the uniform application of the rule ignored the physiological differences between breeds. Today, as shelter-medicine-led pediatric spay/neuter programs (often performed as early as 6 to 8 weeks in shelter settings) remain necessary for shelter animals, private practice veterinarians are shifting toward individualized, breed-specific timelines for owned pets.

How does neutering age change joint-disease risk, and which breeds are most affected?

The link between early gonadectomy and joint disease is strongest in large-bodied breeds. The landmark UC Davis research led by Dr. Benjamin Hart and colleagues (published in Frontiers in Veterinary Science in 2020, and updated through 2024 to cover 40 to 44 breeds) analyzed decades of veterinary hospital records to quantify these risks.

The UC Davis data revealed stark, breed-specific joint disease patterns:

Golden Retrievers: Golden Retriever males are highly sensitive to neutering age. Intact male Goldens have a baseline joint-disease rate (hip dysplasia, elbow dysplasia, or CCL tear) of approximately 5%. However, if neutered before 6 months of age, that risk climbs to 27%—a five-fold increase.
German Shepherd Dogs: German Shepherd Dogs also show significant sensitivity. Intact males have a 7% baseline joint-disease rate, which rises to 21% if neutered under one year of age. Intact females have a 5% baseline risk, which rises to 16% if spayed under one year.
Labrador Retrievers: Intact Labradors have a baseline joint disease rate of 5–6%. If neutered under 6 months, the risk rises to 11–12% for both sexes. While elevated, this is significantly lower than the risk spike seen in Golden Retrievers, illustrating that closely related breeds can have distinct risk profiles.
Rottweilers: Rottweilers are famously predisposed to cranial cruciate ligament tears and osteosarcoma. Early altering significantly increases joint laxity and skeletal maturity delays in this breed, making delay past 12 months a common clinical recommendation.

Why Do Goldens and Labradors Differ?

A persistent question in veterinary orthopedics is why Golden Retrievers show a massive 27% joint-disease risk spike when neutered early, while Labrador Retrievers experience a much milder 12% rise. Researchers hypothesize that this difference is driven by genetic variations in connective tissue composition and receptor density:

Genetic Cartilage Quality: Goldens have a higher genetic predisposition to connective tissue laxity. The loss of estrogen's stabilizing effect on collagen synthesis has a more pronounced impact in this breed.
Growth Plate Sensitivity: Golden Retrievers have a slightly longer growth phase than Labradors, meaning the window of vulnerability to asynchronous growth plate closure is wider.

The Golden Retriever lifetime study and other large cohort studies have confirmed these findings, showing that early-altered large-breed dogs have significantly higher rates of CCL tears and hip dysplasia than their intact peers.

For these predisposed breeds, veterinarians recommend delaying gonadectomy until the growth plates have fully closed, which typically occurs between 12 and 24 months of age, depending on the breed's adult size.

Does spay/neuter timing change cancer risk, and for which breeds?

While gonadectomy eliminates the risk of testicular cancer in males and ovarian/uterine cancers in females, these are relatively uncommon and easily treatable via surgery. In contrast, systemic cancers like lymphoma, osteosarcoma, hemangiosarcoma, and mast cell tumors are highly aggressive, expensive to treat, and often terminal.

The association between early gonadectomy and systemic cancer risk is highly breed- and sex-specific:

Standard Poodles: Standard Poodle males show a dramatic cancer signal. According to the 2020 UC Davis study, male Standard Poodles neutered at one year of age showed a highly significant increase in systemic cancers—predominantly lymphoma—reaching over six times the rate of intact males. Interestingly, Standard Poodles neutered before 6 months or after 2 years did not show this same risk spike.
Golden Retrievers: Golden Retriever females are particularly vulnerable. Intact females have a very low baseline rate of systemic cancers (about 3%). However, spaying a female Golden Retriever at any age up to one year raises the lifetime risk of developing one or more of these cancers (lymphoma, hemangiosarcoma, mast cell tumors) to 18%.
Vizslas: A separate large-scale study of Vizslas found that gonadectomized dogs of both sexes had significantly higher rates of lymphoma, mast cell tumors, and hemangiosarcoma, with the risk rising the younger the dog was altered.
Boxers: Boxers are known to have a high baseline risk for mast cell tumors and lymphoma. Spaying or neutering early removes the protective sex hormones, showing a marked increase in the incidence of these tumors compared to intact Boxers.

These oncological signals suggest that circulating sex hormones may provide a protective, immunomodulatory effect against certain tumor types. In breeds with high baseline cancer rates, keeping the dog intact or delaying surgery past adolescence may help preserve this protective effect.

Ethological and Behavioral Impacts of Gonadectomy Timing

In addition to physical health, veterinarians must evaluate how spay/neuter timing affects canine behavior. Behavior-related issues are a leading cause of owner abandonment and euthanasia in young dogs.

Sex hormones play an important role in behavioral stabilization during adolescence:

Confidence and Fear-Based Aggression: Testosterone in males and estrogen/progesterone in females act as behavioral stabilizers. Studies have shown that early gonadectomy can increase the incidence of fear-based reactivity, resource guarding, noise phobias, and separation anxiety. The loss of hormones during key social development periods can lead to a less confident dog, which manifests clinically as fear-related aggression.
Urine Marking and Roaming: Castration is highly effective at reducing testosterone-driven behaviors like urine marking (reduced by 50–60% post-castration), mounting, and roaming. If a male dog displays severe dominance or roaming behaviors, earlier castration may be indicated.
Trainer and Owner Experience: Active working, performance, or service dogs benefit from delayed alteration, as the circulating hormones support focus, drive, and muscle retention required for high-level tasks.

What about mammary tumors, pyometra, and urinary incontinence on the other side of the scale?

When advising pet owners, clinicians must weigh the skeletal and oncological benefits of delaying gonadectomy against the well-established risks of leaving a female dog intact:

1. Mammary Tumors (Breast Cancer)

Mammary gland tumors are the most common neoplasm in intact female dogs. The traditional rule, based on early studies by Schneider et al. (1969), states that the risk of a female dog developing mammary tumors is:

0.5% if spayed before the first estrus (heat cycle).
8.0% if spayed after the first but before the second heat.
26.0% if spayed after the second heat but before 2.5 years of age.

However, these figures come from a 1969 retrospective study, and a 2012 systematic review (Beauvais et al.) found the overall evidence linking spay timing to mammary-tumor protection to be weaker and less consistent than the classic percentages imply. They are a reasonable starting point, not a precise prediction for an individual dog.

Breed-specific data sharpen the picture. The Veterinary Society of Surgical Oncology (VSSO) places the lifetime risk of a malignant mammary tumor in an intact female dog at roughly 23–34%. Swedish insurance data — the largest population-level source — show how breed and geography move that number. In a cohort of more than 80,000 insured Swedish female dogs (Egenvall et al. 2005), the incidence ran about 111 mammary tumors per 10,000 dogs per year, and a broader summary of the Swedish insured population found roughly 13% of females had developed a mammary tumor by age 10. Breeds flagged as predisposed in the Swedish data include the Leonberger, Irish Wolfhound, Bernese Mountain Dog, Great Dane, Rottweiler, Doberman Pinscher, English Springer Spaniel, and Boxer.

The practical implication is that for a highly predisposed breed such as a Leonberger or Bernese Mountain Dog, the mammary-tumor risk of remaining intact is real and tends to favor spaying before the second heat — whereas for a female Golden Retriever the joint-disease (27%) and systemic-cancer (18%) risks of early spaying tip the decision the other way, toward delaying.

2. Pyometra

Pyometra is a life-threatening uterine infection that occurs in intact female dogs, typically during the diestrus phase of the heat cycle when progesterone levels are elevated. Progesterone causes the uterine lining to thicken and secrete fluid, creating an environment susceptible to bacterial colonization (usually E. coli).

pyometra in dogs is a medical emergency requiring an ovariohysterectomy. Studies show that approximately 25% of intact female dogs will develop pyometra by 10 years of age. The risk increases with age as the uterus undergoes repeated hormonal stimulation. While pyometra is highly treatable if caught early, it carries significant surgical risk in older, compromised patients.

3. Spay-Induced Urinary Incontinence (USMI)

Urinary incontinence is a common side effect of spaying in female dogs, particularly those with an adult weight over 33 lbs (15 kg). The loss of estrogen causes a reduction in urethral closure pressure, leading to involuntary urine leakage when the dog is resting or sleeping.

For some breeds, the timing of the spay directly affects this risk. The 2024 UC Davis updates revealed that in female Shetland Sheepdogs (Shelties), spaying before 24 months of age is strongly associated with an increased risk of urinary incontinence, prompting a recommendation to delay the procedure past 2 years.

Orthopedic Staging: OFA vs. PennHIP in Delayed Gonadectomy

When a clinic recommends delaying spaying or neutering to protect joint health, they should combine this recommendation with proactive orthopedic screening. This is particularly important for dogs with a genetic risk of hip dysplasia.

Veterinary medicine uses two primary methods to evaluate hip joint conformation:

OFA (Orthopedic Foundation for Animals): Requires pelvic radiographs taken in a standard hip-extended view. OFA evaluations are subjective grades assigned by three board-certified radiologists. The main limitation is that OFA only provides an official grade (Excellent, Good, Fair, Borderline, Mild, Moderate, Severe) after the dog reaches 24 months of age, when the skeleton is fully mature.
PennHIP (Pennsylvania Hip Improvement Program): An objective, quantitative method that measures hip joint laxity using a compression view, a distraction view, and a standard hip-extended view. PennHIP generates a Distraction Index (DI), which is a continuous scale from 0 to 1 (with 0 representing a tight joint and 1 representing extreme laxity). PennHIP can be performed as early as 16 weeks of age.

Clinical Use of PennHIP in Timing Decisions

If PennHIP screening at 16 weeks reveals a Distraction Index below 0.3, the dog has tight hips and a very low risk of developing osteoarthritis, even if altered. If the DI is above 0.7, the dog is highly likely to develop hip dysplasia. For dogs with borderline laxity (DI between 0.3 and 0.7), the veterinarian should strongly recommend delaying gonadectomy to 18–24 months to allow the surrounding muscles and ligaments to mature under the influence of testosterone and estrogen, which helps stabilize the joint.

Alternative Surgical Options: Ovary-Sparing Spay and Vasectomy

As veterinarians and owners seek to optimize the balance between preventing pregnancy and preserving hormonal benefits, alternative surgical procedures are gaining interest in clinical practice.

1. Ovary-Sparing Spay (Hysterectomy)

In an ovary-sparing spay (OSS), the surgeon removes the entire uterus and cervix (hysterectomy) while leaving one or both ovaries intact.

Benefits: Because the ovaries remain, the dog continues to produce natural estrogen and progesterone. This preserves the hormonal signals needed for normal growth plate closure and immune function, eliminating the increased risk of joint disorders, urinary incontinence, and certain systemic cancers.
Risks & Considerations: The dog will still go through behavioral heat cycles (estrus), which can attract male dogs, though she will not bleed (as the uterus is gone) and cannot become pregnant. Crucially, because the uterus is completely removed, the risk of pyometra is eliminated. However, if any uterine tissue is accidentally left behind (known as a uterine stump), a "stump pyometra" can still occur. Additionally, the risk of mammary tumors remains identical to that of an intact female dog.

2. Vasectomy

For male dogs, a vasectomy involves cutting and sealing the vas deferens, leaving the testes intact.

Benefits: The testes continue to produce testosterone, ensuring normal musculoskeletal development, muscle mass retention, and metabolic health. The dog is rendered sterile, preventing unplanned litters.
Risks & Considerations: The dog retains all intact male behaviors, including roaming, mounting, marking, and potential inter-dog aggression. The risk of testosterone-driven medical conditions in older age, such as benign prostatic hyperplasia (BPH), perineal hernias, and perianal gland tumors, remains active.
- Clinical Management of BPH in Vasectomized Dogs: Benign prostatic hyperplasia is present in over 95% of intact or vasectomized male dogs by the age of 9. If a vasectomized dog develops symptomatic BPH (manifested by tenesmus, hematuria, or ribbon-like stools), clinicians can manage the condition medically using a 5-alpha-reductase inhibitor like finasteride. Finasteride blocks the conversion of testosterone to dihydrotestosterone (DHT) in the prostate, shrinking the gland without reducing systemic testosterone levels, thus preserving muscle mass and joint protection.

Veterinarians performing these procedures must receive specialized training, as they are technically distinct from standard ovariohysterectomies and castrations.

The 2024 Breed Updates and a Breed-by-Breed Decision Matrix

The 2024 updates from Dr. Hart's team at UC Davis incorporated six additional popular breeds into the existing database: Siberian Husky, German Shorthaired Pointer, German Wirehaired Pointer, Rhodesian Ridgeback, Newfoundland, and Mastiff.

These additions highlighted further nuances:

Siberian Huskies: Showed no significant increase in joint disorders or cancers when altered at any age, suggesting that the standard 6-month window remains acceptable for this breed.
German Shorthaired Pointers: Female GSPs spayed under 1 year showed a significant rise in joint disorders (rising from 0% intact to 20% altered) and systemic cancers (rising from 0% intact to 15% altered), prompting a recommendation to delay spaying until after 11 months.
Newfoundlands and Mastiffs: Both giant breeds showed a strong joint-disease signal when neutered or spayed early, reinforcing the need to delay gonadectomy until after skeletal maturity (18–24 months).

UC Davis also flags a small number of breed–sex combinations for which the data point toward leaving the dog intact unless there is a medical or lifestyle reason to spay or neuter. The clearest case is the female Golden Retriever: because spaying at any age is associated with a higher cancer rate than remaining intact, she is unusual among the breeds studied, and the guidance leans toward leaving her intact (or spaying only for a defined medical reason). The male Standard Poodle shows one of the strongest cancer signals in the dataset — a more than six-fold rise in cancer, mainly lymphoma, with neutering at one year — so the recommendation is to leave him intact or delay well past physical maturity.

Below is the synthesized breed-by-breed decision matrix based on the latest 2024 UC Davis updates and Swedish insurance databases:

Breed & Sex	Recommended Age	Primary Clinical Rationale (Based on UC Davis & Swedish Data)
Small Breeds (< 45 lbs) (Chihuahua, Toy Poodle, Pug, Cavalier)	5–6 Months (Both Sexes)	Low risk of joint disease. Early spaying prevents mammary tumors and pyometra in females. Male Pugs show no early-neuter joint or cancer risk.
Golden Retriever (Male)	Delay past 11 Months (Ideally 18–24 Months)	Intact baseline joint risk is 5%, but rises to 27% if neutered under 6 months.
Golden Retriever (Female)	Keep Intact or Delay past 11 Months	Spaying at any age up to 1 year rises systemic cancer risk (lymphoma, hemangiosarcoma) from 1–2% to 18%.
Labrador Retriever (Both)	Delay past 11 Months	Minimizes moderate joint disease risk elevation (from 5% to 11–12%) without significantly increasing cancer risk.
German Shepherd (Male)	Delay past 11 Months	Intact joint disease risk is 7%, rising to 21% if neutered under 1 year.
German Shepherd (Female)	Delay past 11 Months	Intact joint disease risk is 5%, rising to 16% if spayed under 1 year.
Standard Poodle (Male)	Keep Intact or Delay past 23 Months	Neutering at 1 year increases cancer risk (mainly lymphoma) to over 6x the intact baseline.
Standard Poodle (Female)	Standard (5-6 months or after 1st heat)	No significant joint or cancer risk elevation identified in standard poodle females.
Shetland Sheepdog (Female)	Delay past 23 Months	Spaying earlier significantly increases the risk of urethral sphincter mechanism incompetence (USMI).
Siberian Husky (Both)	Standard (5-6 months)	2024 data shows no significant increase in joint disorders or cancers at any alter age.
German Shorthaired Pointer (Female)	Delay past 11 Months	Significant increase in joint disorders and systemic cancers when spayed under 12 months.
Newfoundland / Mastiff	Delay past 11–23 Months	Large skeletal frame requires prolonged testosterone/estrogen exposure for proper growth plate closure.

Clinical Counseling SOP: Patient Evaluation Questionnaire

To help general practitioners systematically guide owners through the gonadectomy timing decision, clinics should implement a clinical counseling questionnaire. During the initial puppy visits (8 to 16 weeks), the veterinary technician should collect the following information:

Patient Profile:
- Breed: ________________________
- Predicted Adult Weight: [ ] < 45 lbs [ ] 45–75 lbs [ ] > 75 lbs
- Sex: [ ] Male [ ] Female
Breed-Specific Baseline check:
- Does this breed carry a high joint disease or cancer risk in the UC Davis database (PMC7359819)?
- Yes (e.g., Golden Retriever, GSD, Lab, Rottweiler, Standard Poodle) -> Flag for delayed or alternative surgery.
- No (e.g., small breed, Siberian Husky, Pug) -> Standard 5–6 month timing is acceptable.
Owner Management Capabilities:
- Is the owner capable of strictly separating this dog from intact males/females during heat cycles? [ ] Yes [ ] No
- Does the owner's homeowner's insurance, landlord, or local ordinance mandate spay/neuter by a certain age? [ ] Yes [ ] No
- Does the dog attend a daycare or boarding facility with strict alter mandates? [ ] Yes [ ] No
Surgical Choice Selection:
- Standard Gonadectomy (Castration / Ovariohysterectomy)
- Ovary-Sparing Spay (Hysterectomy)
- Vasectomy
Scheduled Procedure Date/Range: ______________ months of age.
Post-Operative / Long-Term Monitoring Plan:
- For delayed/intact females: Scheduled semi-annual mammary palpation beginning at 2 years.
- For delayed/intact males: Scheduled annual prostate palpation beginning at 5 years.

By documenting this process in the PIMS, the clinic ensures a structured, medical-consensus-based decision that minimizes the risks of joint disease and cancer while maintaining responsible population control.

Frequently Asked Questions

What is the best age to spay or neuter a Golden Retriever, Labrador, or German Shepherd?

For male Golden Retrievers and German Shepherds, the data recommends delaying neutering until at least 11–12 months of age (ideally 18–24 months) to avoid a major increase in joint disease. For female German Shepherds and Labradors of both sexes, delaying past 11 months is also recommended. However, for female Golden Retrievers, because spaying at any age under one year is associated with an 18% rate of systemic cancers, keeping them intact or delaying surgery is recommended.

Does delaying neutering increase behavior problems or population-control risk?

Prescribing a delay requires a responsible owner. Intact male dogs are more likely to exhibit roaming, mounting, and urine marking. Intact female dogs will go into heat twice a year, during which they must be strictly separated from intact males to prevent unplanned pregnancies. If an owner cannot manage these behaviors or secure the dog, the population-control benefit of an earlier procedure may outweigh the orthopedic benefits.

Are the UC Davis breed guidelines right for mixed-breed dogs too?

Mixed-breed dogs should be evaluated based on their predicted adult weight. The AKC Canine Health Foundation indicates that mixed-breed dogs with an adult weight over 45 lbs (20 kg) should generally have gonadectomy delayed until 11 to 24 months of age to protect joint health. Mixed-breed dogs under 45 lbs do not show a significant correlation between early alteration and joint disorders, making the standard 5–6 month window appropriate.

Sources

Hart BL, Hart LA, Thigpen AP, Willits NH. "Assisting Decision-Making on Age of Neutering for 35 Breeds of Dogs: Associated Joint Disorders, Cancers, and Urinary Incontinence." Frontiers in Veterinary Science. 2020;7:388. https://pmc.ncbi.nlm.nih.gov/articles/PMC7359819 (PMCID: PMC7359819; PMID: 32733924)
University of California, Davis School of Veterinary Medicine. "When Should You Neuter or Spay Your Dog?" https://www.ucdavis.edu/health/news/when-should-you-neuter-or-spay-your-dog
AKC Canine Health Foundation. "What is the Best Age to Spay/Neuter Your Dog? It Depends." https://www.akcchf.org/breakthrough/what-is-the-best-age-to
American Kennel Club. "A Study Updates Spay-Neuter Timeline Guidance for Popular Dog Breeds." https://www.akc.org/expert-advice/news/study-updates-spay-neuter-guidelines
Torres de la Riva G, Hart BL, Farver TB, et al. "Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers." PLOS ONE. 2013;8(2):e55937. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0055937 (PMCID: PMC3572183; PMID: 23418539)
Egenvall A, Bonnett BN, Öhagen P, Olson P, Hedhammar Å, von Euler H. "Incidence of and survival after mammary tumors in a population of over 80,000 insured female dogs in Sweden from 1995 to 2002." Preventive Veterinary Medicine. 2005;69(1-2):109-127. doi:10.1016/j.prevetmed.2005.01.014
Cornell University College of Veterinary Medicine, Riney Canine Health Center. "Mammary cancer" (Veterinary Society of Surgical Oncology lifetime-risk figures). https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/mammary-cancer
Schneider R, Dorn CR, Taylor DO. "Factors Influencing Canine Mammary Cancer Development and Clinical Behavior." Cancer. 1969;24(2):370–378. (PMID: 5804568)

Vet Med Guide

When to Spay or Neuter Your Dog: Breed, Sex, and Disease Risk Timing