Scientists Warn Small Dogs More Likely to Get Certain Diseases

The type of disease that your dog might get depends on how big it is, according to a new study.

These differing risk levels of certain conditions between larger and smaller dogs may contribute towards the difference in their lifespans, with smaller dogs usually living several years longer than larger ones.

Larger dogs are more likely to suffer from cancers and bone-related conditions, among others, the new paper in the journal PLoS ONE suggests. On the other hand, smaller dogs were more prone to eye conditions and issues with their hearts and lungs.

"Age is the single greatest predictor of disease risk for most causes of mortality in both human and dog populations. However, for many dog diseases, body size is a comparably important predictor of risk," the authors wrote in the paper.

"Companion dogs show considerable variation in longevity across size classes. Between species of mammals, larger ones tend to live longer than smaller ones, while within species, smaller individuals tend to live longer than larger individuals. Accordingly, dogs from larger size classes tend to have a shorter lifespan."

The researchers studied over 25,000 dogs across 238 breeds in the United States, analyzing how health conditions varied across the dogs' lifespan. Rather than larger dogs having many diseases and smaller dogs having fewer, both sizes were more prone to some diseases than others.

"Age in dogs is associated with the risk of many diseases, and canine size is a major factor in that risk. However, the size patterns are complex. While small-size dogs tend to live longer, some diseases are more prevalent among small dogs," the authors wrote.

The results revealed that infectious diseases, bone diseases, gastrointestinal issues, neurological and endocrine problems, and ear/nose/throat issues were more common in larger dogs. In contrast, eye issues, heart problems, respiratory issues, and liver and pancreas issues were seen more frequently in smaller dogs.

There was little difference between larger and smaller breeds regarding risks of kidney and urinary diseases.

"Controlling for sex, purebred vs. mixed-breed status, and geographic region made little difference in all disease categories we studied," the authors wrote.

The authors did not control for individual breeds; instead, they tested against the dog's weight.

While this study does not confirm any causal relationship between dog size, disease, and age, it may help researchers understand why larger dogs have a shorter lifespan than their smaller counterparts.

"These results provide insights into the disease categories that may contribute to reduced lifespan in larger dogs and suggest multiple further avenues for further exploration," the authors said.

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