Geriatric medicine is increasingly important in equine veterinary practice, as aged horses now represent a substantial proportion of the equine population. Although older horses may suffer from different health and welfare issues compared to younger animals, there is a paucity of reliable information on the prevalence of medical conditions and causes of mortality in geriatric horses in the UK. Additionally, previous studies have suggested that owner recognition of health and welfare problems in their aged horses may be suboptimal. A cross-sectional postal questionnaire survey of 918 randomly selected owners of veterinary-registered geriatric horses and ponies (aged ~ 15 years) provided detailed information on demographic characteristics, management practices, preventive health care measures, prevalence of owner-reported health problems and quality of life (QoL). Horses aged ~ 15 years represented 29% of the equine population, with 2% > 30 years old. The overall standard of management was high and there were changes in exercise and feeding practices with increasing horse age. However, the provision of several health care measures, including vaccination, farrier care and routine veterinary checks was reduced as geriatric horses increased in age. Owners frequently observed clinical signs of disease in their animals, with 77% reporting at least one sign, yet a considerably smaller proportion of owners reported their animal currently suffered from a known disease or disorder (31%). Detailed veterinary clinical examination of a subset of horses (n=200) enrolled in the cross-sectional survey demonstrated dental disorders (95%), ocular abnormalities (94%), dermatological conditions (71%) and musculoskeletal disease (lameness observed in 51%) were particularly prevalent, with many animals having multiple disease conditions. Owners tended to underestimate body condition and clinical signs of diseases such as orthopaedic conditions or Pituitary Pars Intermedia Dysfunction frequently appeared to be considered as signs of senescence rather than attributed to a disease process. Relatively poor agreement of owner-reported disease compared to that detected on veterinary examination suggests inaccurate or under-recognition of health problems by owners of geriatric horses, which could lead to a delay in presentation for veterinary treatment. Owners reported that the majority of geriatric animals enjoyed a high quality of life (QoL), with 95% rating their horse's QoL as good or excellent. However, increasing age corresponded negatively with many health-related QoL factors. QoL after the procedure, life-threatening disorders, painful/stressful procedures and veterinary advice were the most important factors in influencing owners' choice of treatment options for a severe illness or injury. To investigate mortality rates, causes of death or euthanasia and factors associated with mortality, horses from the cross-sectional study were enrolled in a cohort study in which follow-up information was obtained over an 18-month period via telephone questionnaires. Overall mortality rate was 11.1 (95% C}, 9.2 -13.2) per 100 horse-years at risk, increasing with increasing horse age. Lameness (24%) and colic (21%) were the most common reasons for euthanasia. Multivariable Cox proportional hazards analysis showed that factors associated with increased risk of mortality were breed (Cob/Cob cross and Thoroughbred/Thoroughbred cross), poor body condition, increasing number of owner- reported clinical signs and the degree to which pain limited normal daily activities. This is the first major study of health and welfare in geriatric horses in the United Kingdom. The reduced frequency of routine preventive health care measures, along with suboptimal owner recognition of health problems may lead to compromised welfare in the geriatric population. Owner perceptions of factors affecting QoL of geriatric horses may prove useful in the development of a QoL assessment tool for aging horses. Results presented in this thesis can be used to inform future veterinary involvement in geriatric equine medicine and in the development of targeted owner education programmes for geriatric health and welfare.

The avascular nature of articular cartilage limits oxygen supply within the tissue. Cartilage, therefore, is under physiological hypoxic conditions. Oxygenation gradients are estimated from 10% at the surface to 1% at the deepest layer. Nonetheless, chondrocytes have been reported to be able to survive and are well-adapted to such an environment. We hypothesised that low oxygen tensions favour chondrocyte metabolism based on their nature and literature reviews.

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