New Study Examines How Dog Size Influences Disease Risk

A dog’s size affects the diseases they likely will experience. Small dogs tend to live longer than large- and giant-breed dogs, but they are also at higher risk for some diseases. For example, small-breed dogs are more likely to die from endocrine diseases, whereas large-breed dogs are more likely to die from musculoskeletal and gastrointestinal (GI) issues. Recent research using owner-reported data on the disease history of companion dogs enrolled in the Dog Aging Project studied how a dog’s size and age influences disease history patterns. 

Data collection and analysis

The study data was based on 27,541 survey records from companion dog owners and provided information that included dog demographics, health status, and owner demographics. The research team evaluated 13 disease categories reported in 500 or more dogs. To understand how disease history trended across age and size, researchers looked at the lifetime prevalence of each disease category in three ways:

  • A function of age and weight
  • A function of age, weight, and the age-by-weight interaction
  • A function of age, weight, and the age-by-weight interaction, adjusted for the dog’s sex, breed status, and census division

The dogs ranged in age from puppies to senior dogs, with a median age of 7 years. The dogs were 50% male and 50% female and also were equally distributed by breed, with 49% purebreds and 51% mixed breeds representing 238 breeds. Labrador and golden retrievers made up the majority of the purebred dogs. Respondents were from across the United States and most commonly reported living in suburban locations. 


Adjustments for sex, breed status, and geographic region had no notable impact on the associations for the disease categories evaluated. Results included:

  • Skin conditions — Reports showed that 7,915 dogs had a history of skin disease. Older dogs were more likely to have skin conditions, and large dogs were more commonly affected than small dogs. Toy dogs had the lowest rate across age, and skin conditions progressed more often in each successively larger size category, regardless of age. Lifetime prevalence of skin conditions also increased with the dog’s weight. 
  • Infectious diseases — Reports showed that 7,339 dogs had a history of infectious disease, with puppies having a 25% incidence of infectious disease, and other age groups ranging from 25% to 28%. Dogs less than 22 pounds had the lowest reported history of infectious disease at 19%, with all other size classes ranging from 27% to 30% prevalence. 
  • Orthopedic conditions — Reports showed that 5,287 dogs had a history of orthopedic disease. Lifetime incidence increased with age, especially in larger dogs, and lifetime prevalence of orthopedic conditions was much greater in large-breed senior dogs.
  • Gastrointestinal (GI) conditions — Reports showed that 3,914 dogs had a history of GI disease. GI disease incidence increased from 7% in puppies to 18% in senior dogs, and slightly increased from 14% in dogs less than 22 pounds to 16% in dogs more than 88 pounds. Incidence increased steadily in size groups with age, and dogs more than 88 pounds had a notably higher lifetime prevalence across all ages. 
  • Ear, nose, and throat (ENT) conditions — Reports showed that 3,569 dogs had a history of an ENT condition, which increased from 3% in puppies to 25% in senior dogs and from 13% in small-breed dogs to 16% in large dogs. 
  • Cancer — Reports showed that 1,751 dogs had a history of cancer. Incidence increased from less than 1% in puppies to 15% in senior dogs. Lifetime prevalence by size was 4% in small dogs and 6% to 8% in large dogs. The prevalence increase by age was much more pronounced in dogs more than 66 pounds. 
  • Neurological conditions — Reports showed that 1,324 dogs had a history of neurological disease. Incidence increased from less than 1% in puppies and young dogs to 12% in senior dogs. Dog size was not associated with any notable trends, but giant-breed dogs had a much steeper increasing pattern across age than dogs less than 88 pounds. 
  • Endocrine conditions — Reports showed that 913 dogs had a history of endocrine disease. Lifetime prevalence was less than 1% for puppies and young dogs, 4% for older adult dogs, and 8% for senior dogs. Dogs experienced a similar increase in incidence as they aged, regardless of their size, but the larger the dog, the higher the lifetime prevalence curve.
  • Ocular conditions — Reports showed that 3,625 dogs had a history of ocular disease. Incidence increased from 5% in puppies to 28% in senior dogs. Smaller dogs had a higher disease incidence at 17%, compared with 10% in dogs more than 88 pounds. 
  • Kidney and urinary conditions — Reports showed that 2,122 dogs had a history of kidney or urinary disease. Prevalence increased from 2% in puppies to 15% in senior dogs. Lifetime prevalence was highest in dogs less than 22 pounds at 9% and lowest in dogs greater than 88 pounds at 6%.
  • Cardiac conditions — Reports showed that 1,567 dogs had a history of cardiac disease, with incidence increasing from less than 1% in puppies and young dogs to 14% in senior dogs. Dogs weighing less than 22 pounds had an 11% lifetime prevalence, while dogs more than 88 pounds had a 2% lifetime incidence. Lifetime prevalence was not only higher in small dogs but was also associated with a significantly steeper increase across age groups.
  • Liver or pancreas conditions — Reports showed that 970 dogs had a history of liver or pancreas disease. Incidence increased from less than 1% in puppies and young dogs to 8% in senior dogs. Smaller dogs were most commonly affected at 6%, compared with large dogs at 2%. Dogs less than 22 pounds had a significantly higher lifetime prevalence of liver disease.
  • Respiratory conditions — Reports showed that 950 dogs had a history of respiratory disease, with incidence increasing from less than 1% in puppies to 8% in senior dogs. Prevalence decreased with size, affecting 6% of small dogs and 3% of large dogs. 

In summary, conditions that included ocular, cardiac, liver or pancreas, respiratory, and infectious diseases were more common in small dogs, while skin, orthopedic, GI, ENT, cancer, neurological, and endocrine conditions were more common in large dogs. 

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