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only cats that died before 12 years of age (17). Although malignant neoplasia is often life-limiting, routine veterinary evaluation of older cats for neoplastic disorders has been recommended because earlier diagnosis may enable interventions that increase longevity and improve palliative care as well as the provision of more-informed choices for owners (34). The current study results supported the hypothesis that longevity in crossbred cats exceeds purebred cats. Direct comparison of median overall longevity values showed that crossbred cats outlived purebred cats by 1.5 years (crossbred cats: 14.0 years compared with purebred cats: 12.5 years). Within those cats dying at or after 5 years of age, after accounting for bodyweight, sex, neutering and insurance status, crossbred cats outlived purebred cats by 0.6 years. In support, an Australian survey on currently-living pet cats reported a significantly higher median age for crossbreds (7.0 years) compared with purebreds (5.5 years) (3). 14 Cats have been kept as pets by humans for 10,000 years (39) but it is during the past 150 years that cats have especially been selectively bred for show and novelty (12). Purebred cats comprised 8.3% of the population in the current study. Although the proportion of UK owned cats that are purebred is currently around 10% (40), this value is predicted to rise, bringing an expansion in both the recognition and impact of breedrelated anomalies and genetic disorders (41, 42). The substantial longevity deficit identified for purebred cats in the current study warrants further investigation to better understand and manage the mechanisms involved. It may be that purebred cats express more recessive disorders because of greater homozygosity for deleterious genes, i.e. inbreeding depression (43) but other genetic and non-genetic differences may additionally contribute. It is also worth noting that, although purebred status was significantly associated with a reduced longevity, only 8.5% of longevity variation was explained by the final model used in the current study. This implies substantial roles in feline longevity for factors not included in the current study such as diet (44), vaccination (45), outdoor access (31) and obesity (46). Despite the superior longevity identified in crossbreds, it is notable that longevity varied widely between pure cat breeds, suggesting the importance of improved understanding of associations between breed and longevity. The Birman, Burmese, Siamese and Persian lived as long as or longer than crossbreeds whereas the Bengal, Abyssinian, Ragdoll, Maine Coon and British Shorthair breeds showed reduced longevity. A 15 Swedish insurance study similarly identified equivalent or greater age-based survival for Birman, Norwegian, Persian and Siamese cats compared with domestic cats (2). Longevity variation between breeds may partially be explained by differing breed bodyweights; lighter breeds have greater longevity than heavier breeds (47). Differing breed predispositions to specific diseases may also contribute to longevity variation (9). Larger breed-specific studies would enable greater longevity precision and reporting of within-breed risk factors for compromised longevity. Such studies are especially important for less popular breeds where smaller gene pools for breeding may increase predispositions for inherited disease (10). It is worth noting that both overall and breed-specific longevity is influenced by the right of owners to opt for termination of life for their cats. In the current study, more than 85% of deaths involved euthanasia, with statistically different proportions of crossbred and purebred cats being euthanased (86.0% vs. 81.9% respectively). Euthanasia decision-making is complex and emotionally intense both for owners (48) and veterinarians (49). Greater understanding of the human factors involved in pet euthanasia decisions may ameliorate the psychological burden on owners and veterinarians as well as improving the quality of the decisions made. Maximum bodyweight values recorded after 6 months of age were negatively associated with longevity in the current study. In cats that died at 5 years of age or older, cats weighing less than 3 kg lived 1.7 years longer on average than cats weighing between 4 16 and 5 kg. A negative association between bodyweight and longevity has previously been reported in dogs (14) and was hypothesised to result from genetic and pathological effects induced by artificial selection for extremes of size and growth (50-53). The bodyweight associations with longevity identified in the current study may have been partially confounded by breed and obesity effects that could be explored in future studies (46). Although the study indicated an association between insurance and reduced longevity, the direction of any causality requires careful consideration. Insured animals may revert to being non-insured as they age because of increasing insurance costs or exclusions (54, 55). The current study used insurance values at death and thus the negative association identified may have resulted from increasing insurance policy cancellation with advancing age. Neutering was associated with 0.6 years greater longevity in females and 1.7 years greater longevity in males. Neutering offers health benefits including reduced risk of asthma, gingivitis and hyperactivity in both sexes and decreased
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