“Bort” (pictured) is one of the oldest male Rottweilers living in North America that investigators put to work to discover the linkage between lifelong gonad function, late-life frailty, and overall mortality risk. (Credit: Center for Exceptional Longevity Studies, Gerald P. Murphy Cancer Foundation.)
In A Nutshell
- Male Rottweilers neutered before age 2 faced much higher death rates when health declined in old age compared to dogs neutered later
- Dogs that kept their testicles for 10+ years showed no increase in death risk as health problems mounted in their senior years
- The study suggests early-life hormones may create lasting protection that helps aging bodies tolerate accumulated health problems
- Findings came from an observational study of 87 exceptionally long-lived male Rottweilers, so results may not apply to all dogs or prove causation
Neutering debates just got more complicated. An observational study of exceptionally long-lived Rottweilers reveals that male dogs castrated before their second birthday face a hidden penalty that surfaces only in old age: once frail, they die at higher rates than dogs neutered later in life.
Dogs neutered before age two showed sharply higher death rates as their health declined in old age. But in dogs that kept their testicles for at least a decade, worsening health problems didn’t lead to earlier death.
Published in Scientific Reports, the findings move beyond the usual questions about whether and when to neuter. Instead of focusing on if early neutering shortens lifespan or increases disease risk, scientists at the Gerald P. Murphy Cancer Foundation asked a different question: Does neutering timing change how dangerous old-age health decline becomes decades down the road?
Their answer points to something veterinarians and pet owners rarely consider about this common surgery. The body’s hormonal environment during the first years of life may create lasting effects that shape how well an aging dog handles mounting health problems.
How Scientists Measured Aging’s Toll on 87 Senior Dogs
Frailty describes what happens when health problems pile up over time. Vision fades, joints stiffen, memory slips, diseases accumulate. Researchers measured this in 87 male Rottweilers living across North America, all at least 13 years old and among the oldest of their breed.
A veterinarian scored each dog on 34 health measures through detailed phone interviews with owners. These included appetite, stamina, eyesight, hearing, balance, mental sharpness, bladder control, and pain levels, plus diagnosed conditions like heart disease and cancer. Higher scores meant more health problems.
Twenty-seven dogs had never been neutered. Sixty others lost their testicles at various ages, most often because owners had finished breeding or had no intention to breed, with some neutered for medical or conformation reasons. After scoring, researchers tracked the dogs until death to see whether declining health predicted death differently based on how long each dog had maintained an intact reproductive system.
Early Surgery, Late Consequences
Mortality patterns were stark. Among dogs with similar health problems, early-neutered dogs died much faster as they declined, while the link between declining health and death disappeared in dogs that kept their testicles for more than 9.8 years.
This pattern held even after accounting for body weight, when dogs were born, and why they were neutered. Statistical models confirmed that each additional year with testicles reduced death risk as health declined in old age.
Testosterone comes from testicular cells that respond to signals from the brain. This hormonal system (called the HPG axis) regulates far more than reproduction. Previous research in aging men has linked low testosterone and related hormone problems to declining health. But this dog study took a different angle.
Lead author David J. Waters and his team wanted to know if keeping the hormonal system intact during early life might protect dogs from the worst consequences of health decline once it inevitably arrives. Data said yes. Early castration appeared to remove a protective factor that would otherwise help aging bodies cope with accumulated health problems.
One possible explanation involves a hormone called luteinizing hormone, which rises sharply after neutering when normal signals from the testicles stop. Studies in older men have linked high levels of this hormone to health decline independent of testosterone. Another possibility: early hormone disruption causes long-lasting cellular changes that permanently alter how bodies respond to aging stresses.
The study didn’t measure hormone levels directly but used how long dogs kept their testicles as a stand-in. A follow-up analysis limited to dogs whose neutering dates were confirmed in medical records produced identical results, suggesting owner-reported timelines were accurate.
Why the Same Health Problems Kill Some Dogs But Not Others
Most aging research focuses on preventing health decline or slowing how fast it happens. Waters and colleagues shifted that focus. They wanted to understand why the same level of health problems kills some dogs quickly while others with identical issues live longer.
Data suggests the answer depends on something established decades earlier. Dogs neutered in their first two years developed a vulnerability that lay dormant until old age, when declining health triggered death at rates that intact dogs never experienced.
For decades, neutering debates have centered on disease risk and longevity. Does early surgery increase cancer rates? Does it cause joint problems? Do neutered dogs live longer or shorter lives? This research introduces a new dimension: resilience. Not just whether neutering affects disease development but whether it changes how well bodies handle the inevitable decline of aging.
Two dogs might accumulate health problems at similar rates, but one dies months earlier because his body lost the capacity to tolerate those problems. Across all dogs studied, typical survival after health assessment was just over six months. Early-neutered dogs faced a much steeper decline once health problems mounted compared to dogs with longer testicular exposure.
Human studies support the idea that declining health doesn’t affect everyone the same way. Swedish researchers once compared two groups of 70-year-olds born decades apart. Both groups had similar health problems using identical measures, but death risk associated with those health problems differed significantly between the groups. If the impact of health decline can vary between human populations born in different eras, it can also vary between dogs with different hormonal histories.
What This Means for Dogs and Their Owners
Results came from only male Rottweilers, a breed with shorter average lifespans than many large dogs. Whether the same patterns appear in females, other breeds, or mixed-breed dogs remains unknown. Neutering wasn’t assigned randomly but reflected real-world owner decisions. These associations can’t prove that early neutering caused the increased vulnerability.
To check for bias, researchers examined whether the reason for neutering affected results. It didn’t. Whether dogs were castrated to prevent breeding or because of pre-existing problems like hip dysplasia, the pattern held: longer testicular exposure was linked to better tolerance of health decline in old age.
This study doesn’t tell owners when to neuter. Dogs neutered at all ages eventually reached exceptional longevity, living 30% longer than typical Rottweilers. What differed was what happened when their health declined. Most neutering decisions consider factors like preventing unwanted litters, managing aggression, or treating medical conditions. This research adds another consideration: how castration during early development might influence the body’s capacity to withstand health decline decades later.
Future studies could explore whether similar patterns exist in other breeds or female dogs. Researchers could also investigate why early neutering might amplify the deadly effects of health decline in old age.
Practical takeaways remain unclear. Does this mean owners should delay neutering until dogs reach ten years old? Not necessarily. Researchers didn’t compare specific neutering ages head-to-head, and later neutering carries its own risks. What this research offers is a new way to think about this common surgery. Effects of removing reproductive organs may not fully appear until old age, when the body faces accumulated damage from years of living. Early-life decisions about hormones set a tone that echoes through the entire lifespan, determining not whether dogs decline but whether that decline becomes deadly.
Disclaimer: This article discusses scientific research findings and is intended for informational purposes only. It does not constitute veterinary medical advice and should not be used as a substitute for professional veterinary consultation. The study discussed is observational and cannot prove cause and effect. Decisions about neutering should be made in consultation with a licensed veterinarian who can evaluate your individual dog’s health, breed, lifestyle, and specific circumstances. Do not change your pet’s medical care based solely on information in this article.
Paper Summary
Methodology
Researchers enrolled 87 male Rottweilers who had lived to at least 13 years, about 30% longer than average for the breed. All dogs were part of the Exceptional Aging in Rottweilers Study and lived across 28 U.S. states and Canada. Veterinary staff conducted standardized phone interviews with owners to assess 34 different health variables, including appetite, strength, sensory function, mobility, cognition, pain levels, and diagnosed diseases. Each variable was scored as absent, present, or mild (controlled with medication), and scores were combined into a health decline index. Twenty-seven dogs had never been neutered, and 60 had been castrated at various ages. Neutering age was confirmed through medical records for 72% of neutered dogs, with the remainder based on owner-reported dates. Researchers tracked all dogs from health assessment until death to calculate death risk as health declined across different groups based on how long they kept their testicles.
Results
Dogs neutered before age two showed much higher death risk as health problems mounted in old age. Dogs neutered between two and 9.8 years showed a smaller effect. Dogs with more than 9.8 years of testicular exposure showed no increase in death risk as health worsened. Statistical models confirmed this pattern held after accounting for body weight, birth year, and reason for neutering. Analysis showed each additional year with testicles reduced the death risk tied to declining health. Typical survival after health assessment was about six months overall, with cancer and neurological conditions as the most common causes of death.
Limitations
Findings came from only male Rottweilers, so results may not apply to females or other breeds. Neutering was not assigned randomly but reflected owner decisions influenced by breeding plans, medical issues, or physical defects. While accounting for the reason for neutering didn’t change results, other unmeasured factors could still contribute to the observed patterns. Researchers did not measure testosterone or other hormone levels directly, instead using how long dogs kept their testicles as a substitute measure. Body weight assessments came from owner reports rather than veterinary examinations. Sample size limited the ability to evaluate multiple factors simultaneously or explore more detailed age ranges for neutering effects.
Funding and Disclosures
Grants from The IAMS Company, P&G Pet Care, and the Rottweiler Health Foundation to the Murphy Cancer Foundation supported this research. Lead author David J. Waters received additional support from a Brookdale National Fellowship in gerontology and a Glenn Award for research in biological mechanisms of aging. Authors declared no competing interests.
Publication Information
Waters, D.J., Maras, A.H., Fu, R., Carrillo, A.E., Schafer, M.H., Chiang, E.C., & Suckow, C.L. (2025). Longer duration of intact hypothalamic–pituitary–gonadal (HPG) axis buffers the adverse impact of late-life frailty in male dogs. Scientific Reports, 15, 34467. doi:10.1038/s41598-025-20700-8
Should also apply to people. We neutered several kids who then went on to have short life spans compared to the non neutered kids. Though it was a fluke but evidently not. Uptake is keep those nuts on as long as possible.