Why do big dogs live shorter lives? - study

It’s well-known among dog owners that smaller breeds live longer than large ones. For example, Great Danes live only around six to eight while small breeds like the Maltese, Bichon Frise, Shi Tzu, chihuahua, Australian cattle dog, Yorkshire terriers, beagles, Jack Russell terriers, and toy poodles have an average lifespan –if well taken cared for – of about 16 years.  But even small dogs can get a variety of chronic diseases. 

Dogs can suffer any disease and chronic condition as humans do. Now, a study of more than 27,000 dogs living in the US and 238 breeds has linked dog size to varying patterns of risk for health conditions over the course of a dog’s lifespan. Biostatistician Yunbi Nam of the University of Washington in Seattle and colleagues just presented such findings in PLOS ONE under the title “Dog size and patterns of disease history across the canine age spectrum: Results from the Dog Aging Project.”

Evidence suggests that larger dogs do not tend to have more health conditions, but that dogs of different sizes may face different levels of risk for different conditions. However, more research is needed to clarify links between dog age, size, and disease prevalence, the authors wrote. 

Overall, larger dogs in the study were more likely to have faced certain types of health conditions at some point in their lives, including cancer, bone-related disease, gastrointestinal problems, ear/nose/throat issues, neurological and endocrine conditions, and infectious diseases. Meanwhile, smaller dogs were more likely to have experienced ocular, cardiac, liver/pancreas, and respiratory diseases. The history of kidney/urinary disease did not differ significantly for larger versus smaller dogs.

For many types of conditions including cancer, ocular, cardiac, orthopedic, and ear/nose/throat conditions—different dog sizes were associated with differing patterns of risk over the course of a dog’s lifespan. The results held up even after the researchers statistically accounted for the dogs’ sex, where they lived, and whether they were purebred or mixed-breed.

Why do big dogs live shorter lives?

The researchers note that this study does not confirm any causal relationship between dog size, age, and disease. Still, the findings could help lead to a deeper understanding of the types of conditions that may underlie the lower lifespan of larger dogs. For instance, within the disease categories explored in this study, future research could focus on age and size patterns associated with specific conditions.

The authors add: “These results provide insights into the disease categories that may contribute to reduced lifespan in larger dogs and 

We also found that the association between age and lifetime disease prevalence varied by dog size for many conditions including ocular, cardiac, orthopedic, ear/nose/throat, and cancer. Controlling for sex, purebred vs. mixed-breed status, and geographic region made little difference in all disease categories we studied. Our results align with the reduced lifespan in larger dogs for most of the disease categories and suggest potential avenues for further examination.

MEANWHILE, a new study at the University of Washington at Madison has discovered that knowing what dogs like to watch on TV or video could help veterinarians assess their vision. uses a dog's interest in a variety of video content to better measure the quality of its vision.

Have you ever wondered what kind of TV shows your dog might choose if they could work the remote control? Even now, there are many “dog music” videos on YouTube that let you test what canines are like. The study, published in the journal Applied Animal Behavior Science under the title “Screen interaction behavior in companion dogs: Results from a dog-owner survey,” provides some answers, but the study was more interested in solving a longstanding problem in veterinary medicine than turning canine companions into couch potatoes.Veterinary ophthalmologist Prof. Freya Mowat and her team wanted to determine factors, including age and vision, that influence a dog’s interest in interacting with video content. Ultimately, the goal of the study, which was launched two years ago, was to support the development of more sensitive ways to assess canine vision – something that has been sorely lacking in veterinary medicine.

“The method we currently use to assess vision in dogs is a very low bar. In humans, it would be equivalent to saying yes or no if a person was blind,” Mowat said. “We need more sensitive ways to assess vision in dogs, using a dog eye chart equivalent. We speculate that videos have the potential for sustaining a dog’s attention long enough to assess visual function, but we didn’t know what type of content is most engaging and appealing to dogs.”

They found that dogs are most engaged when watching videos that feature other animals. Content featuring other dogs was the most popular. But if a National Geographic documentary about canine evolution seems too highbrow for your four-legged friend, Scooby-Doo might be a perfectly acceptable option as well.

To better understand the type of content dogs might be most attracted to on screen, Mowat created a web-based questionnaire for dog owners around the globe to report the TV-watching habits of their canine companions. Participants responded to questions about the types of screens in their homes, how their dogs interacted with screens, the kinds of content their dogs interacted with the most, as well as information about their dog’s age, sex, breed and where they live. They also provided descriptions of their dogs’ behavior when watching videos. Most commonly, dog owners described their pets’ behavior as active — including running, jumping, tracking action on screen and vocalizing — compared with passive behaviors like lying down or sitting. Dog owners also had the option to show their dog four short videos featuring subjects of possible interest, including a panther, a dog, a bird and traffic moving along a road. They were then asked to rate their dog’s interest in each video and how closely the dog tracked the moving objects on the screen.

How dogs interact with screens

Mowat received 1,600 responses from dog owners across the world, and of these, 1,246 ultimately completed the study. She found that age and vision were related to how much a dog interacted with a screen. Sporting and herding dog breeds appear to watch all content more than other breeds. Video content featuring animals was the most popular, with other dogs being by far the most engaging subjects to watch. Humans do not appear to be very appealing for dogs to watch, ranking ninth out of 17 predetermined categories. Cartoons were engaging for more than 10% of dogs. Movement on screens was a strong motivator for screen attention.

Mowat says she plans to build on the results of this study. Future research will focus on the development and optimization of video-based methods that can assess changes in visual attention as dogs age as well as answer questions that could help our four-legged friends age as gracefully as possible. “We know that poor vision negatively impacts the quality of life in older people, but the effect of aging and vision changes in dogs is largely unknown because we can’t accurately assess it,” she concluded.  “Like people, dogs are living longer, and we want to make sure we support a healthier life for them as well.”

Another goal for Mowat is to compare how a dog’s vision ages compared with the human or humans with whom they share a home. “Dogs have a much shorter lifespan than their owner, of course, and if there are emerging environmental or lifestyle factors that influence visual aging, it might well show up in our dogs a long time before it shows up in us. Our dogs could be our sentinels – the canine in the proverbial coal mine.”