A recent study published in the journal Scientific Reports delves into the lifespan of different dog breeds and its correlation with their evolutionary journey through domestication by humans and subsequent artificial selection for desired traits.
The findings of this study hold significant implications for canine welfare and are of interest to welfare organizations, breeding associations, and dog enthusiasts worldwide.
Human domestication of dogs from their ancient wolf ancestors is a well-established fact, dating back approximately 16,000 years, as supported by genomic and archaeological evidence.
Recent endeavors in artificial selection aimed at amplifying desirable traits have led to a notable loss in genetic diversity and a remarkable array of phenotypic variations. This loss was exacerbated by breeding practices such as repeated use of popular sires, intending to maintain pedigree diversity by limiting gene flow between breeds.
Certain breed standards emphasized achieving specific physical attributes by exaggerating phenotypic characteristics, resulting in various disorders associated with conformation and hereditary pathology.
Studies comparing the lifespan of purebred and crossbred dogs have indicated that crossbreds enjoy a survival advantage of 1.2-1.3 years, attributed in part to ‘hybrid vigor,’ resulting from reductions in deleterious genes inherited from both parents in purebreds.
While the impact of inbreeding depression or hybrid vigor on domestic dogs remains inconclusive, researchers have cataloged approximately 700 hereditary traits and disorders. The prevalence of diseases in many purebred populations raises concerns about their overall health.
Study Details
The study incorporated data from 584,734 dogs in the United Kingdom, encompassing breed information, sex, crossbreeding status, date of birth, postal code, death date (if applicable), and other identifying details. Data was sourced from academic institutions, animal welfare charities, pet insurance firms, veterinary corporations, and breed registries.
Purebred dogs were classified by size (large, medium, small) within each breed. Their cranial index, indicating skull width-to-length ratio, was determined, further classifying them as dolichocephalic (long-faced), mesocephalic (medium-proportioned), or brachycephalic (flat-faced).
The research employed maximum likelihood estimation and Kaplan-Meier survival curve analysis to explore censored data, considering variables such as cephalic index, sex, size, breed, and parental lineage. The Cox proportional hazards model assessed proportional mortality risk differences.
Key Findings
Of the 584,734 dogs studied, 284,734 were deceased. Survival probabilities were lowest for geriatric dogs and highest for juveniles, with crossbreds exhibiting a median survival of 12 years and purebreds 12.7 years.
Variations in longevity were observed across breeds, with some breeds prone to early mortality (e.g., mastiffs, St. Bernards) and others displaying lower risks (e.g., border terriers, Italian greyhounds). Breed size significantly influenced lifespan, with large breeds showing lower survival estimates than smaller ones.
The study also identified interactions between size and cephalic index, revealing faster time-to-death for brachycephalic breeds, particularly in larger sizes.
Phylogenetic analyses highlighted strong associations between median lifespan distribution and evolutionary lineage, indicating lifespans of breeds within a clade were more similar than expected by chance.
Conclusions
While previous research suggested shorter lifespans for purebreds compared to crossbreds, this study presents a nuanced perspective, highlighting substantial variability across breeds. Further investigations, incorporating geographical and environmental factors along with causes of death, are essential to enhance veterinary understanding and promote better care practices for purebred dogs.
