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Dog size is directly linked to different types of disease

A comprehensive study involving over 25,000 dogs across 238 breeds in the United States has uncovered significant links between the size of a dog and its risk for various health conditions. 

Conducted by Yunbi Nam and colleagues from the University of Washington, the study marks a significant step in understanding why smaller dogs generally have a longer lifespan compared to their larger counterparts.

The Dog Aging Project

“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,” noted the researchers.

“In this study we seek to quantify how the pattern of disease history varies across the spectrum of dog size, dog age, and their interaction.”

To investigate, the experts analyzed data from 27,541 dogs, part of the ongoing Dog Aging Project. This extensive dataset allowed for a comprehensive view of how size impacts health risks across a dog’s life.

“The Dog Aging Project (DAP) provides a unique opportunity to investigate how the lifetime prevalence of different conditions varies across age and size in a large community-based population of companion dogs,” wrote the study authors. 

“Additionally, we explore whether the adjustment for the dog’s sex, breed status (purebred vs. mixed-breed status), and the census division defined by the dog’s residence address impacts this relationship.”

Key findings about dog size

The results of the study indicate that large dogs are more prone to suffer from certain health conditions such as cancer, bone-related diseases, and gastrointestinal issues.

Bigger dogs were also found to be more likely to have problems related to ears, nose, and throat; neurological and endocrine conditions; and infectious diseases. 

On the other hand, smaller dogs tend to be more susceptible to diseases affecting the eyes, heart, liver, pancreas, and respiratory system. 

Furthermore, the prevalence of kidney and urinary diseases did not show a significant difference between large and small dogs.

Groundbreaking approach 

The study is groundbreaking in its approach to understanding how risks for various health conditions vary with the size of the dog throughout its lifespan. 

Notably, the researchers found distinct patterns of risk associated with various diseases such as cancer, ocular, cardiac, orthopedic, and ear/nose/throat conditions, depending on the dog’s size.

Even after accounting for variables such as the dog’s sex, living environment, and whether they were purebred or mixed-breed, the clear link between size and disease risk remained evident.

The experts said their results provide insights into the disease categories that may contribute to reduced lifespan in larger dogs and suggest multiple avenues for further exploration.

Dog size study strengths and limitations 

“Our study has several strengths and limitations that should be noted. Strengths include the large sample size of this study, which allows us to estimate patterns with high power across the whole age and size spectrum,” wrote the researchers.

“Additionally, we have a very diverse sample of dogs distributed across the entire United States. Since the sample is not veterinary-hospital or clinic-based it may be more representative of the general population of dogs.” 

“Conversely, while our observations can suggest which conditions manifest differently across age and size, they do not prove any causal relationships due to the cross-sectional nature of the analysis. Over time, longitudinal data will be collected on these dogs, and we will be able to examine disease incidence.”

The study is published in the journal PLOS ONE.

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