A new study of “old Rottweilers” has revealed that keeping their testicles longer can help them age better, revealing how hormones shape resilience in both dogs and humans.
In dogs and humans, frailty associated with old age signals a decrease in the body’s resilience to everyday stressors such as illness or injury, and has a significant impact on activities of daily living. Even minor physical or health challenges can lead to major loss of function.
In a new study, at the end of October in Scientific Reportsresearchers studied 87 exceptionally old purebred male Rottweilers to see how the length of time they held their testicles influenced frailty and survival into old age, and how this could translate into older human males.
As detailed by , each dog was monitored from the moment the fragility score was assigned until death. The researchers used Cox proportional hazards models (a standard method of survival analysis) to see how frailty predicted mortality, overall and in groups with different durations of gonadal exposure (i.e., how long the dogs kept their testicles “intact” before being castrated).
It was found that the frailty increased with age. Older dogs had higher “Fragility Index” (FI) scores on average.
Not so much, early castration was associated with worse outcomes. Dogs neutered before the age of two had a 16% increase in mortality risk for each small increase (0.01) in frailty score.
Those that remained intact for more than about 10 years did not show an increase in mortality with greater frailty. Essentially, the fragility was less lethal for them.
Each additional year of gonadal integrity reduced the risk of frailty-related death by about 1%. This “dampening effect” was not explained by other factors, such as excess weight, year of birth or castration for medical reasons.
The pattern remained even when only cases with castration dates confirmed by veterinary records were included (to eliminate owner recall bias). In other words, the longer a dog’s hormonal system remained intact, the better it was able to “deal” with fragility when it eventually appeared.
“Os Male dogs with the shortest duration of testicular exposure had a very high mortality risk associated with frailty in old age, while the deadly consequence of increased frailty disappeared in males with the longest gonad exposure,” concluded the study’s lead and corresponding author, David Watersdirector of the Murphy Foundation’s Center for Exceptional Longevity Studies, cited by New Atlas.
But how do these conclusions relate to humans?
“Historically, dogs have played a key role in research into endocrine hormones, including the discoveries of insulin and the ability to reduce prostate cancers through androgen ablation,” Waters said.
Now, this study extends human research showing that low testosterone levels and HPG axis dysfunction are linked to frailty, suggesting that Dogs may be a useful comparative model for studying hormone-related resilience to aging.
The hypothalamic-pituitary-gonadal (HPG) axis is the feedback loop between the brain and gonads (testicles or ovaries) that maintains sexual hormone levels at healthy values.
As New Atlas points out, understanding when hormonal disruption occurs can be crucial for both veterinary guidance and human geroscience, since Early hormonal loss can establish “limits of resilience” long-term biologicals.
“Our study marks an important step towards a better understanding of resilience to fragility, moving forward with the perspective that, By preventing deterioration of the HPG axis, we can maintain an internal hormonal environment that buffers the adverse impact of frailty”, concludes Waters.
