Neutering Effects on Dog Lifespan and Age-Related Disease Risks

Jump To Section

• Dog Aging Project Study Design
• Neutering Status and Lifespan
• Disease Patterns in Neutered Dogs
• Four Biological Sexes in Dogs
• Hormonal Changes and Aging Biology
• Full Transcript

Dog Aging Project Study Design

Dr. Matt Kaeberlein, MD, PhD, explains the Dog Aging Project's approach to studying canine longevity. The longitudinal study aims to capture genetic and environmental diversity. Dr. Kaeberlein tells Dr. Anton Titov, MD, that the project does not control for variables like neutering status. Instead, researchers want to observe this natural variety to identify strong correlations with aging.

The current cohort is primarily based in the United States. Approximately 80-90% of dogs in this population are sterilized. This creates a unique opportunity to study both neutered and intact animals within the same environment.

Neutering Status and Lifespan

Research from the Dog Aging Project team reveals important findings about neutering and lifespan. Dr. Matt Kaeberlein, MD, PhD, references work by colleagues Daniel Promislow and Kate Creevy. When researchers control for body size—the greatest predictor of canine lifespan—a pattern emerges.

Sterilized dogs show a slightly longer life expectancy compared to intact dogs. This finding holds significance for understanding how hormonal changes affect aging processes. Dr. Matt Kaeberlein, MD, discusses these findings with Dr. Anton Titov, MD, during their conversation about canine aging research.

Disease Patterns in Neutered Dogs

The spectrum of fatal diseases differs significantly between neutered and intact dogs. Dr. Matt Kaeberlein, MD, PhD, emphasizes this crucial distinction during his discussion with Dr. Anton Titov, MD. While sterilized dogs may live slightly longer, they die from different age-related conditions.

This suggests that neutering doesn't simply slow aging uniformly. Instead, it modifies disease risk profiles. Understanding these differential disease patterns could provide insights into how hormones influence specific aging pathways.

Four Biological Sexes in Dogs

Dr. Matt Kaeberlein, MD, PhD, introduces the concept of four unique biological sexes in companion dogs. This classification results from common sterilization practices in the United States. The four categories include intact males, intact females, sterilized males, and sterilized females.

Each group represents fundamentally different biological states due to hormonal differences. Dr. Matt Kaeberlein, MD, explains to Dr. Anton Titov, MD, that this creates a more complex model for studying aging. Researchers must account for these four distinct groups when analyzing age-related health outcomes.

Hormonal Changes and Aging Biology

Sterilization causes substantial changes in sex hormones that fundamentally alter canine biology. Dr. Matt Kaeberlein, MD, PhD, emphasizes the importance of these hormonal shifts. These changes affect the underlying biological aging processes in complex ways.

The Dog Aging Project team remains highly aware of sterilization's role in aging research. They consistently analyze how neutering status and sex interact with age-related health outcomes. Dr. Kaeberlein's discussion with Dr. Anton Titov, MD, highlights how this natural experiment provides unique insights into hormonal aging mechanisms.

Full Transcript

Dr. Anton Titov, MD: What about the differences in hormonal levels? I understand that most adults in the United States are neutered, so that makes them castrated irrespective of their sex. Certainly in New York, dogs don't bark—I'm sure it's part training, but that probably has to do with the fact that they're neutered. Whereas in other parts of the world, they mostly are not, and I can attest they certainly bark. So how do you control for those hormonal varieties?

Dr. Matt Kaeberlein, MD: Yeah, so really good question. I would say the first real answer is we don't even try to control it. We want to capture that variety.

The whole point of a longitudinal study is to get as much of the genetic and environmental diversity as we can to try to figure out what are the strong correlations. But you're right: in our cohort, which for now is restricted to the United States, the majority of dogs—I think it's in the 80 to 90% range—are sterilized. So we are overrepresented, certainly for sterile dogs.

Having said that, particularly among purebred dogs, there are a significant fraction of dogs that are not sterilized, and so they go through their entire life intact. We can ask questions about the relationship between sterilization status and age-related health outcomes because we have large numbers of both types of dogs.

I will say there have been prior studies, some of which have been done by members of the Dog Aging Project team—Daniel Promislow and Kate Creevy and others—looking at this question. It's interesting because it seems as though when you control for body size—and body size is the greatest predictor of lifespan in dogs—dogs that are sterilized do have a slightly longer life expectancy.

But what's potentially more interesting is the diseases that sterilized dogs die from, or at least which are associated with death. Sterilized dogs are somewhat different than the spectrum of diseases that intact dogs die from.

So I think the take-home message is that sterilization and hormonal changes with age play a role in the risk of certain diseases with age. The extent to which they affect the underlying biological aging process, I think, is a different question and one that's a little bit less clear.

So I think it's important, and it is absolutely something that we're aware of. A couple of points to make: I think it's funny because when you talk to the average person, certainly they're aware that dogs are sterilized typically in the United States, but they don't appreciate the fact that that sort of creates four unique sexes in companion dogs. There are intact males, intact females, sterilized males, and sterilized females.

I think it's important to appreciate that when you sterilize an animal, there are pretty substantial changes in the hormones—sex hormones in particular—which really fundamentally change the biology of that animal. So we are very aware of that and always pay attention to the role that sterilization and sex could have on different age-related health outcomes.

Dr. Anton Titov, MD: Oh, that's certainly very interesting. That's a fascinating, true animal model that probably approximates human life more than some other models do.