Bias in canine lifespan estimates through right censored data

Lifespan of companion dogs seen in three independent primary care veterinary clinics in the United States

Background

The privately owned companion dog is an emerging model in comparative medicine, notably because it shares the human environment including its risk factors, is affected by many analogous age-related diseases, receives comparable medical care, and has excellent veterinary medical data available.

Past studies of dog lifespan have used academic, corporate or insurance data. While independent primary care data exist for the UK, none have as of yet been published for the US. This study analyzed data from three independent primary care US veterinary hospitals and identified factors that influence lifespan and mortality in a cohort of n = 20,970 privately owned dogs using Kaplan-Meier survival estimators and Cox Proportional Hazards modelling, including body size as a covariate.

Results

As previously reported, body size was negatively correlated with lifespan. Gonadectomy was associated with a longer lifespan, with the effect being stronger in females than in males. This lifespan advantage was conserved in gonadectomized female dogs that lived to at least ages 5 and 8 years. We did not find significant differences in lifespan between purebred and mixed breed dogs; however, breeds with larger effective population sizes and/or lower inbreeding coefficients had median survival times 3–6 months longer than breeds with smaller effective population sizes or higher inbreeding coefficients, indicating that these measures of genetic diversity may be affecting breed lifespans. We also found that dog breeds belonging to the “Mountain” ancestral group had median survival times that were 3.5–4.6 years shorter than other purebred dog groups, which remained significant even when correcting for body size.

Conclusions

Our findings show that it is possible to obtain and analyze data from independent veterinary clinics in the US, an approach that could be useful for studies of comparative epidemiology under the One Health and One Welfare paradigms. We also show that the lifespan effects of gonadectomy are not identical between the sexes and should be investigated separately by sex in future analyses. More research is needed to further clarify the influence of age at gonadectomy, as well as the factors leading to the observed differences in lifespan in the “Mountain” ancestral group and in dog breeds of varying inbreeding coefficients and effective population sizes.

West Highland White Terriers under primary veterinary care in the UK in 2016: demography, mortality and disorders

Background

The West Highland White Terrier (WHWT) is a relatively common breed in the UK, although Kennel Club registrations have declined in recent years. The VetCompass™ Programme collates de-identified clinical data from primary-care veterinary practices in the UK for epidemiological research. Using VetCompass clinical data, this study aimed to characterise the demography, longevity and common disorders of WHWTs under primary veterinary care in the UK.

Results

WHWTs comprised 6605/905,544 (0.7%) dogs under veterinary care during 2016 from 886 clinics. Mean adult bodyweight was 9.6 kg (standard deviation [SD] 1.8 kg). Males (10.1 kg, SD 1.8 kg) were heavier than females (9.0 kg, SD 1.6 kg) (P < 0.001). Median age was 7.8 years (interquartile range [IQR] 4.3–11.1). Median longevity was 13.4 years (IQR 11.0–15.0). Males (13.8 years) outlived females (12.9 years) (P = 0.045). The most common grouped causes of death were lower respiratory tract (10.2, 95% CI: 5.5–16.7), neoplastic (10.2, 95% CI: 5.5–16.7) and spinal cord disorder (7.8, 95% CI: 3.8–13.9). Overall, 71.5% WHWTs had > 1 disorder recorded during 2016. The most prevalent specific disorders were periodontal disease (15.7, 95% CI: 14.1–17.3), otitis externa (10.6, 95% CI: 9.3–12.0), overgrown nails (7.2, 95% CI: 6.2–8.4), allergic skin disorder (6.5, 95% CI: 5.5–7.7) and obesity (6.1, 95% CI: 5.1–7.2). The most prevalent grouped disorders were cutaneous (22.7, 95% CI: 20.9–24.6), dental (17.8, 95% CI: 16.2–19.6) and aural (12.3, 95% CI: 11.0–13.8). The median age of dogs affected with the 27 most common disorders varied from 6.7 (pododermatitis) to 13.9 years for cataracts.

Conclusions

These findings highlight that, despite a recent decline in popularity, WHWTs are still relatively common in the UK. Dental disease, ear disease, overgrown nails, allergic skin disorder and obesity were identified as common health issues within the breed. Cutaneous disorders were the most common disorder group in the breed but showed a lower prevalence than might be expected. These results can be used by breeders, veterinary practitioners and owners as an evidence base to predict, prevent and manage key health and welfare issues for WHWTs.

Disorders of Bulldogs under primary veterinary care in the UK in 2013

The Bulldog is a popular companion breed in the UK despite widely reported disease predispositions. This study aimed to characterise the demography, mortality and common disorders of Bulldogs under veterinary care in the UK during 2013. VetCompass collates anonymised clinical data from UK primary-care veterinary practices for epidemiological research. The clinical records of all Bulldogs available in the VetCompass study dataset were reviewed manually in detail to extract the most definitive diagnoses recorded for all disorders that existed during 2013 and for all deaths. Bulldogs comprised 1621 (0.36%) of 445,557 study dogs. Bulldogs increased from 0.35% of the 2009 birth cohort to 0.60% in 2013. Median longevity was 7.2 years, which was lower in males (6.7 years) than females (7.9 years) (P = 0.021). The most prevalent fine-level precision disorders recorded were otitis externa (n = 206, prevalence 12.7%, 95% CI: 11.1–14.4), pyoderma (142, 8.8%, 95% CI: 7.4–10.2) and overweight/obesity (141, 8.7%, 95% CI: 7.4–10.2). The most prevalent disorder groups were cutaneous (n = 463, prevalence: 28.6%, 95% CI: 26.4–30.8), ophthalmological (292, 18.0%, 95% CI: 16.2–20.0), aural (211, 13.0%, 95% CI: 11.4–14.8), enteropathy (188, 11.6%, 95% CI: 10.1–13.3) and upper respiratory tract (171, 10.5%, 95% CI: 9.1–12.1). Provision of an evidence base on the most common disorders and causes of mortality within breeds can support owners, breeders and the veterinary profession to improve health and welfare within these breed.

Risk Factors Associated with Lifespan in Pet Dogs Evaluated in Primary Care Veterinary Hospitals

The objective of this population-based retrospective cohort study was to identify factors associated with lifespan in pet dogs evaluated at primary care veterinary hospitals. Dogs ≥3 mo of age that visited any of 787 US hospitals at least twice from January 1, 2010, through December 31, 2012, were included. Survival curves were constructed for dogs by reproductive status, breed, body size, and purebreed (versus mixed-breed) status. Multivariate Cox proportional hazard regression was performed to identify factors associated with lifespan. There were 2,370,078 dogs included in the study, of whom 179,466 (7.6%) died during the study period. Mixed-breed dogs lived significantly longer than purebred dogs, and this difference was more pronounced as body size increased. Controlling for other factors, dogs of either sex had a greater hazard of death over the study follow-up period if sexually intact rather than gonadectomized. For dogs who lived to 2 yr of age, the hazard of death decreased with increasing frequency of dental scaling. Our findings support previous reports of the impact of body size and gonadectomy on lifespan and provide new evidence in support of ultrasonic dental scaling and mixed breeding.

Longevity and mortality in Kennel Club registered dog breeds in the UK in 2014

Background

The domestic dog is one of the most diverse mammalian species, exhibiting wide variations in morphology, behaviour and morbidity across breeds. Therefore, it is not unexpected that breeds should also exhibit variation in mortality and longevity. While shorter longevity per se may not necessarily be a welfare issue, a generally foreshortened lifespan in a breed that is accompanied by a high prevalence of a particular cause of death may reveal potentially serious welfare concerns and highlight scope to improve breed welfare. Survey data gathered directly from owners offer useful insights into canine longevity and mortality that can support the overall evidence base for welfare reforms within breeds.

Results

Mortality data on 5663 deceased dogs registered with the UK Kennel Club were collected from an owner-based survey. The most commonly reported causes of death were old age (13.8%), unspecified cancer (8.7%) and heart failure (4.9%); with 5.1% of deaths reported as unknown cause. Overall median age at death was 10.33 years (interquartile range: 7.17–12.83 years). Breeds varied widely in median longevity overall from the West Highland Terrier (12.71 years) to the Dobermann Pinscher (7.67 years). There was also wide variation in the prevalence of some common causes of death among breeds, and in median longevity across the causes of death.

Conclusion

Substantial variation in the median lifespan and the prominent causes of death exists across breeds. This study has identified some breeds with both a low median lifespan and also a high proportional mortality for one or more specific causes of death that should be considered as both potential welfare concerns as well as opportunities for improvement.

Electronic supplementary material

The online version of this article (10.1186/s40575-018-0066-8) contains supplementary material, which is available to authorized users.