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What conditions are seen most commonly in primary care visits, and how are they different between mixes and purebreds?
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A summary of “Lifetime Prevalence of Owner-Reported Medical Conditions in the 25 Most Common Dog Breeds in the Dog Aging Project Pack,” by Forsyth et al.
Forsyth, Kiersten K, et al. “Lifetime Prevalence of Owner-Reported Medical Conditions in the 25 Most Common Dog Breeds in the Dog Aging Project Pack.” Frontiers in Veterinary Science, vol. 10, 3 Nov. 2023.
Link (open access): https://doi.org/10.3389/fvets.2023.1140417
Summary by: Charlie Clarke and Jessica Hekman
This study collected user survey data as part of the Dog Aging Project.
Its aims were to:
- Estimate the lifetime prevalence of the most common disorders in the 25 most common breeds.
- Identify differences in lifetime medical condition prevalence between mixed breed and purebred dogs.
- Identify differences in lifetime medical condition prevalence between the most common 25 breeds compared to all mixed breed and purebred dogs.
- Determine whether or not there is a difference in disorder prevalence between purebred and mixed breed populations.
Data Collection
The University of Washington undertook the Dog Aging Project in 2014, led by Dan Promislow, Kate Creevy, and Matt Kaeberlin. This citizen science project recruited dog owners to contribute annual survey data and veterinary records, and participate in a prospective study following dogs over the course of their entire life. One of the surveys that participating owners filled out was the health and life experience survey. This survey included questions about dog (and human) demographics, health status, diet, behavior, physical activity, and environmental factors. The data from the health section of this questionnaire was used to determine the top 10 reported medical conditions found in the top 25 AKC recognized breeds.
Results
Data for 27,541 dogs was collected. The most common medical issues reported in this group of dogs is listed below. Unsurprisingly, the list suggests that the most commonly seen conditions are not serious ones with large welfare impacts on dogs:
| Medical Condition |
| Dental Calculus |
| Extracted Teeth |
| Dog Bite |
| Fractured Teeth |
| Seasonal Allergies |
| Giardia |
| Osteoarthritis |
| Ear Infection |
| Torn/Broken Nail |
| Chocolate Ingestion |
Several of these conditions were significantly different in frequency between purebred and mixed breed dogs.
| Medical Condition | Mixed Breed Prevalence (%) | Purebred Prevalence (%) | More common in |
| Extracted Teeth | 13.48 | 5.95 | Mixes |
| Dog Bite | 11.94 | 9.58 | Mixes |
| Fractured Teeth | 7.16 | 5.95 | Mixes |
| Seasonal Allergies | 7.14 | 6.49 | Mixes |
| Ear Infection | 6.18 | 8.36 | Purebreds |
| Torn/Broken Nail | 5.66 | 4.83 | Mixes |
| Chocolate Ingestion | 5.36 | 4.01 | Mixes |
Note that the difference in frequency is less than 3% for all disorders except for extracted teeth. With such a large sample size (more than 27,000 dogs!), it is typical that even very small differences may be statistically significant – but that does not mean that they are noticeable or relevant to dog owners.
A longer list of 53 common medical conditions was also reported. There are too many of these to list all the significant differences here, but a list of the most significant differences (p < 0.005) are:
- More common in purebreds: cataracts, UTIs, coccidia, pancreatitis, corneal ulcer, IVDD, retained deciduous teeth
- More common in mixes: itchiness, laceration, underbite
Of these 53 conditions, 13 were more common in mixes and 14 in purebreds. The most significant finding was that tooth extraction is more common in mixes, with both the largest percentage difference and the smallest p value (largest statistical significance) at 1.66×10-98. This is a truly exceptionally small (significant!) p value and strongly suggests a real finding (either that mixes are more prone to dental disease, or that their owners are more prone to address dental disease). The next two most significant findings were KCS (dry eye) at 2.46×10-13 and entropion (misshapen eyelids that rub against the eyes) at 1.37×10-12. (Both KCS and entropion are closely associated with brachycephaly, entropion specifically with brachycephaly + loose skin, and are highly heritable – i.e., related to a dog’s breed rather than how their owner cares for them.)
The ten most common medical conditions were also assessed by breed. The list was different for different breeds as compared to all purebreds. For example, Labrador Retrievers were more likely to have ear infections, arthritis, and cruciate rupture than other purebreds. Golden Retrievers were more prone to ear infections and chronic hot spots. German Shepherds were more prone to seasonal allergies and hip dysplasia – the HD finding being hugely significant at 9.76×10-19.
The prevalence of dogs with no reported medical conditions was compared between purebreds and mixed breed dogs. Mixed breed dogs have a lifetime prevalence of no medical conditions at ~20% while the entire population of purebred dogs have a lifetime prevalence of no medical conditions at ~22% – very similar numbers, though, again, statistically significant due to the large sample size. When broken down by breed, there were certain breed populations that had significantly fewer reported medical conditions. For example, Australian Shepherds had a ~30% rate of no reported medical conditions, and Siberian Huskies had a ~35% rate of no reported medical conditions. Certain breeds also showed lower rates of no reported medical conditions, such as Greyhounds at ~8.8%. (Again, this may be because the dogs are healthier, or because the owners were less likely to bring them in for diagnoses.)
Discussion
This paper has received a lot of attention online and has been framed as an answer to the question “which are healthier, mixed-breed or purebred dogs?”. Indeed, the authors of this paper also frame it as an answer to this question. Note that the paper does not address healthspan or lifespan. It also addresses only the most common reasons that dogs visit a veterinarian. A dog may be diagnosed with cancer only once in its lifetime, but have multiple ear infections or tooth cleanings.
It is unsurprising that the most common disorders for which dogs are treated do not have serious welfare consequences. However, this paper does not attempt to address the questions of life-threatening diseases in specific breeds, and we would not expect those once-in-a-lifetime diagnoses to appear here. Moreover, looking at the list of 53 most common medical conditions, several (chronic hot spots, hip dysplasia, dry eye, entropion) are related to a dog’s breed, highly heritable (affected more by genetics than by how the dog is managed), and are more common in purebreds. Dermatological disorders (seasonal allergies – more common in mixes – and ear infections – more common in purebreds) are typically complex disorders with both a genetic and environmental component. They can range from mild to causing serious welfare issues, and we can’t know how serious the ones described in this study are.
Finally, while this paper’s extraordinary sample size allows the researchers to ask some very interesting questions, we must remember that with epidemiological data such as this, we are never sure exactly what question people are answering. Why do owners of mixes report dental problems so much more commonly than owners of purebreds? Because they are more likely to request dental care? Because they are more likely to remember it? Or because their dogs are more likely to need it? We cannot be sure which reason actually lies behind a very significant statistical correlation.
Summary
Different medical conditions affect breeds at different prevalences. This data may be useful to purebred dog breeders attempting to identify disorders at high prevalence that should be prioritized for breeding away from, such as cruciate rupture for Labrador Retrievers or hip dysplasia for German Shepherds. While this data is less useful for mixed breed breeders, because the population is very heterogeneous, it does suggest that skin allergies may be something to assess in individual populations. Dental disease appears to be an issue for all dog owners to take more seriously.
The paper showed clearly that most dogs visit the vet most often for less serious issues, and that a study of the most common issues addressed by veterinarians will not cover many of the more serious conditions that breeders seek to address (such as heart disease and cancer). While more disorders were attributed to mixed breeds in the top 10, they were not disorders with serious welfare significance, nor were they disorders with a significant genetic component. (Dermatological disorders may have significant welfare implications, and are seen at increased risk in mixed vs purebred dogs depending on the type of disorder.) Looking at the longer list of less common disorders revealed some with more serious welfare implications (IVDD, dry eye, entropion) with a much larger genetic component.
This work by the Functional Dog Collaborative is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.