The Companion Dog as a Model for the Longevity Dividend

Abstract

The companion dog is the most phenotypically diverse species on the planet. This enormous variability between breeds extends not only to morphology and behavior but also to longevity and the disorders that affect dogs. There are remarkable overlaps and similarities between the human and canine species. Dogs closely share our human environment, including its many risk factors, and the veterinary infrastructure to manage health in dogs is second only to the medical infrastructure for humans. Distinct breed-based health profiles, along with their well-developed health record system and high overlap with the human environment, make the companion dog an exceptional model to improve understanding of the physiological, social, and economic impacts of the longevity dividend (LD). In this review, we describe what is already known about age-specific patterns of morbidity and mortality in companion dogs, and then explore whether this existing evidence supports the LD. We also discuss some potential limitations to using dogs as models of aging, including the fact that many dogs are euthanized before they have lived out their natural life span. Overall, we conclude that the companion dog offers high potential as a model system that will enable deeper research into the LD than is otherwise possible.

Figure 1.

Survivorship curves (A) and age-specific mortality curves (B) for a population following a Gompertz mortality model (Gompertz 1825). According to the Gompertz mortality model, mortality increases exponentially over time, with µ_x = αe^βx, where µ_x is the mortality rate at age x, α is the “baseline” mortality rate, and β is the rate of aging. The black line shows standard mortality. Survivorship can be increased (or mortality lowered) either by reducing the baseline mortality (red) or by slowing the rate of aging (blue). Most real-world examples show a much greater reduction in α than in β. (C) The more realistic Siler mortality model (Siler 1979) is shown, where ${\mu }_x={\alpha }_1{e}^{-{\beta }_{1}x}+{\alpha }_2+{\alpha }_3{e}^{{\beta }_{3}x}$.

Figure 2.

Longevity dividend (LD) calculations for dogs from the VetCompass database (O’Neill et al. 2013). (A) Survival curves for all dogs (blue line) and hypothetical survival curves for populations in which a single cause of mortality is omitted (see text for details). All-cause mortality curves (B) and survivorship curves (C) are shown for actual data (yellow), and based on fitted mortality curves using the Siler model (Siler 1979), ${\mu }_x={\alpha }_1{e}^{-{\beta }_{1}x}+{\alpha }_2+{\alpha }_3{e}^{{\beta }_{3}x}$, for all mortality (blue) and for reduced aging rate, where β₃ is the rate of aging and has been reduced by 10% (red).

Figure 3.

Proportion of dogs dying of cancer for specific breeds. (Left) Veterinary Medical Database (VMDB) data. (Right) VetCompass data. Blue lines indicate large breed dogs (VMDB: Labrador Retriever, Golden Retriever, Rottweiler, and Boxer; VetCompass: Labrador Retriever, Golden Retriever, Rottweiler, and German Shepherd). Orange line indicates medium breed dogs (VMDB: Beagle; VetCompass: Border Collie, American Staffordshire Terrier, English Springer Spaniel, Cocker Spaniel), and the red lines indicate small-breed dogs (VMDB: Miniature Poodle, Dachshund, and Yorkshire Terrier; VetCompass: Cavalier King Charles Spaniel, Jack Russell Terrier, West Highland White Terrier, and Yorkshire Terrier). Notice the trend of high rates of cancer in both data sets with a significant decline in the oldest ages.