Mortality and life table analysis in a young cohort of pet cats in the UK

Objectives
Mortality data represent an important resource for understanding population health that previously have mostly been extrapolated from veterinary records. The aims of this study were to explore mortality for a cohort of pet cats in the UK using data from owner-completed questionnaires, thus potentially representing a more comprehensive population, and to determine the all-cause mortality and survival probabilities.

Methods
Data were collated from the ‘Bristol Cats’ study questionnaires, owner communications and medical records for the cohort’s first 8 years of life. Mortality was classified by organ system, disease or event, and analysed by age and life stage. Age-specific mortality and cumulative survival probability curves were constructed using life table analysis.

Results
Of 2444 cats recruited into the ‘Bristol Cats’ study, at least 362 died before reaching the age of 9 years. The most common cause of death in cats up to the age of 8 years was road traffic accident (RTA; 45.6%). For kittens (aged <1 year), the most common causes were RTA (61.2%), feline infectious peritonitis (11.9%) and other trauma (7.5%). The most common causes of mortality in young adult cats (aged 1–6 years) were RTA (49.6%), non-specified (14.4%), renal disease (6.5%) and cardiovascular disease (6.5%). Cats aged up to 2 years had an annual probability of dying in the range of 2.8–3.1%, which decreased between 2 and 3 years of age to 1.7%. Thereafter, the probability of dying gradually increased with age, with the oldest age group (aged 7–8 years) having a 3.6% probability of dying.

Conclusions and relevance
This study identified important differences in causes of mortality for the first two life stages in a population of cats that may not be fully accounted for in medical records. Life table analysis documented an increasing probability of death with age after year interval 2–3 with a higher mortality risk for cats aged up to 2 years.