Assessing quality of life in older horses

As is the case in the human population (Office for National Statistics, 2019), through increasing life expectancy, the equine population is ageing (Welsh et al, 2016), comprising a considerable proportion (28–34%) of geriatric animals (McGowan et al, 2010; Ireland et al, 2011a; Bushell and Murray, 2016). Similar to the situation described for humans (Haywood et al, 2005), older horses represent a very diverse sector of the equine population and this diversity is reflected across age, health status and healthcare requirements. As horses get older, owners frequently make considerable changes to their management practices, including diet and exercise (Ireland et al, 2011a). However, there is limited available information regarding the reasons for, and impact of, horse owners making these changes. Weight management and use of supplements were reported to be the most common aspects of daily management that owners changed as their horse aged (Bushell and Murray, 2016). Dietary alterations such as the increased use of hay replacers and complete chopped fibre or mash feeds are likely to be beneficial in older horses with advanced dental disease (Ireland et al, 2011a), whereas the widespread use of in-feed supplements, despite a paucity of evidence regarding their oral bioavailability and efficacy, may represent an area for improved owner education (Bushell and Murray, 2016). Furthermore, with increasing horse age, the frequency of routine veterinary attention and several preventive healthcare measures, including farrier care and vaccination, are reduced (Mellor et al, 2001; McGowan et al, 2010; Ireland et al, 2011b).

The term ‘quality of life’ (QoL) is used extensively in human and veterinary healthcare. Despite this, there is a lack of consistency regarding its definition in the literature, and in veterinary medicine QoL is often considered synonymously with welfare (Broom, 2007; Taylor and Mills, 2007). However, QoL is a broader concept with a slightly different emphasis to welfare, encompassing physical health, psychological state (including negative and positive affective states) (Taylor and Mills, 2007) and ‘general enjoyment of life’ (Broom, 2007). Although the vast majority of owners consider their older horses to have good or excellent QoL, increasing horse age is associated with reduced owner QoL rating (Ireland et al, 2011c).

Assessing quality of life

Quality of life assessment is well established in human medicine, with a large number of published generic and disease-specific measurement scales (Bowling, 2001). For example, different QoL assessments have been validated for monitoring the effect of pain management (Skevington et al, 2001) and chronic disease in humans (Sprangers et al, 2000; Osborne et al, 2003; Öztürk et al, 2011) and used to evaluate age-related changes in QoL (Blane et al, 2004; Wiggins et al, 2004). There are numerous applications beyond evaluating the status of an individual patient. In a practice setting, QoL instruments are used as an adjunct to more objective clinical indicators for evaluating the effectiveness of medical treatments (Higginson and Carr, 2001). For example, a simple QoL assessment using linear visual analogue scales to measure eight variables including appetite, dyspnoea, feelings of wellbeing, and social activity, was evaluated in geriatric patients with chronic obstructive pulmonary disease (Katsura et al, 2003). When used in an outpatient clinic, the QoL scale was reported to correlate well with more complex health-related and respiratory-specific QoL instruments and to improve alongside improvement in several clinical parameters following a pulmonary rehabilitation programme (Katsura et al, 2003). In pharmaceutical development, QoL assessment is increasingly used as an outcome measure in clinical trials and drug licencing applications (Chassany et al, 2002). QoL measures are also used in veterinary pharmaceutical development, as well as randomised controlled clinical trials in small animal medicine, such as owner completion of a cardiac-specific questionnaire to measure QoL in a trial comparing two diuretics in dogs with congestive heart failure (Peddle et al, 2012).

In human medicine, the gold standard QoL assessment instrument is a validated questionnaire with well-established reliability (Chassany et al, 2002; Varricchio and Ferrans, 2010). Ideally information about an individual's perspective or subjective feelings would be gathered directly from that individual, for example using patient self-assessment questionnaires. However, in veterinary medicine, this information must necessarily be obtained from human observers, interpreting an animal's behaviour or physiological characteristics in order to assess QoL indirectly. Generic QoL instruments using owner questionnaires have been developed in small animal medicine (Wojciechowska et al, 2005; Mullan and Main, 2007; Bijsmans et al, 2016). Table 1 shows some of the World Health Organization (2020) QoL domains and facets, together with examples of how these could be adapted for use in an equine veterinary setting.

Health-related quality of life

Ageing is characterised by an increasing susceptibility to the development of multiple chronic diseases (Fabbri et al, 2015). Geriatric cats and dogs rarely have a single disease, but instead have a unique combination of diseases together with varying degrees of organ dysfunction (Fortney, 2004). In human medicine, more than 55% of elderly people have multimorbidity (defined as the coexistence of two or more chronic diseases), which is associated with poor QoL (Marengoni et al, 2011).

Multimorbidity is also highly prevalent in older horses and there is a high burden of chronic disease within the geriatric equine population (Ireland et al, 2012a; Welsh et al, 2016). For example, pituitary pars intermedia dysfunction (Figure 1) was a comorbidity in nearly half of horses with more than one chronic disease (Welsh et al, 2016). Although the study population included animals of all ages, cases of multimorbidity frequently involved conditions that are prevalent in older horses: 26% of horses diagnosed with osteoarthritis also had a history of laminitis, and 8% of laminitis cases had severe equine asthma as a comorbidity (previously recurrent airway obstruction) (Welsh et al, 2016). Where therapeutic and management recommendations for concurrent conditions are potentially contradictory, the treatment of multimorbidities in older horses may be particularly challenging.

Owners frequently consider many clinical signs of disease as benign changes associated with normal ageing (Ireland et al, 2012b), meaning that some chronic diseases may be unrecognised by owners. While owners report a high degree of confidence in their ability to recognise obesity and weight loss (Bushell and Murray, 2016), owner underestimation of body condition in older horses is common (Ireland et al, 2012b). Additionally, clinical signs associated with some highly prevalent conditions in geriatric horses, including dental disease, ocular pathology and cardiac abnormalities, may not be apparent to owners based on external observations of their horse (Ireland et al, 2012a). Therefore the health status of an older horse will be an important determinant of its QoL, and inevitably, health is likely to be the primary focus of veterinary assessments.

While veterinary surgeons are well placed to assess the health-related QoL (HRQoL) of their patients, it is important to recognise that this includes more than a thorough clinical examination. Assessment of a person's health status will primarily encompass evaluation of the impact of specific clinical signs or physical limitations resulting from disease, such as pain or fatigue, whereas measures of HRQoL are broader, including mental and social wellbeing (Haywood et al, 2005).

Questionnaires for assessment of HRQoL have been developed for use in dogs (Reid et al, 2013) and cats (Freeman et al, 2016; Noble et al, 2019). In addition to physical domains, these instruments include domains that assess mental wellbeing such as distress, anxiety (Reid et al, 2013) and emotions (Freeman et al, 2016; Noble et al, 2019), and also social functioning, as determined based on the animal's engagement with the owner or carer and their environment (Freeman et al, 2016). Several specific instruments have been described in small animal medicine for assessment of HRQoL in a range of conditions including canine chronic pain (Wiseman-Orr et al, 2004), idiopathic epilepsy (Wessmann et al, 2014), atopic dermatitis (Favrot et al, 2010), feline diabetes mellitus (Niessen et al, 2010) and cardiac disease (Freeman et al, 2012). Since welfare requirements of horses differ from those of small animals, direct extrapolation of these published tools is not possible. However, collectively they provide a valuable resource from which to derive some domains that should be included in equine HRQoL assessment.

Activities of daily living and social interaction

While poor health has been used as a proxy measure of QoL in human geriatric medicine, it is increasingly recognised that health represents only one component. Patients with significant medical problems do not necessarily have QoL ratings proportionate with their health (Carr and Higginson, 2001). This is important since simply equating poor health with poor QoL neglects people's ability to adapt and overcome or cope with illness, and suffering from chronic disease may not necessarily lead to poor QoL. Therefore many of the health and utility tools widely used to measure QoL in geriatric patients include a large component devoted to activities of daily living, mental health and social interactions (Haywood et al, 2005), which are considered more frequently by older people as determinants of their QoL.

Similarly, activities of daily living are important for older horses. Activities of daily living such as level of activity when turned out at pasture or lying down when stabled or resting (Figure 2) were significantly associated with increased risk of mortality in older horses where owners reported some degree of compromise or impairment (Ireland et al, 2011d). Importantly, owners are readily able to assess activities of daily living, and consider these to be major determinants of QoL. Several management factors related to activities of daily living and social interactions (such as nutrition, comfort, company of other horses, regular field turnout and human contact) were more frequently considered by owners to influence QoL of older horses than health-related factors such as preventive healthcare and effective analgesia (Ireland et al, 2011c). Using pituitary pars intermedia dysfunction and osteoarthritis as examples, Table 2 summarises some potential components of HRQoL assessment in animals diagnosed with a chronic disease or disorder. In addition to taking a thorough history and performing a comprehensive clinical examination, HRQoL assessment should include disease-specific clinical assessments as well as evaluation of general health (both physical and mental), the horse's environment and its ability to perform key activities of daily living (Table 2).

Individualised quality of life assessment

The major challenge in measuring QoL lies in its uniqueness to individuals. In human medicine, there is concern that many of the existing assessment tools fail to take account of this by imposing standardised models of QoL, with preselected domains. Therefore, there is growing awareness of the importance of individualised assessments, where patients identify key life activities relating to their own QoL. Early examples of this are the Subjective Domains of Quality of Life Measure (SDQLM) (Bar-On and Amir, 1993) and the Schedule for the Evaluation of Individual Quality of Life – Direct Weighting (SEIQoL-DW) (O'Boyle et al, 1993), where respondents identify areas of importance in their life, rate these areas on an individually generated scale and rank their importance. The SEIQoL-DW has been reported to be a feasible and valid QoL instrument (Wettergren et al, 2009), which is of particular use for exploring determinants that contribute to individuals' QoL (Moons et al, 2004). This method has been successfully adapted for owner-perceived QoL assessment in dogs, where owners of both healthy dogs and those with spinal cord injuries volunteered the same broad domains of mobility, play or mental stimulation, health and companionship (Budke et al, 2008), which could be readily be adapted to apply to older horses (Figure 3).

Equine quality of life assessment

While it is an area of ongoing research, no validated QoL instrument is currently available in equine medicine. However, various equine welfare assessment tools are available, focussing primarily on environmental assessment or health indicators, including body condition score, hydration status, cardiorespiratory parameters, and lameness (reviewed by Hockenhull and Whay, 2014) or pain scales (reviewed by van Loon and Van Dierendonck, 2018). Additionally, there is growing interest in behavioural ethograms and evaluation of horses' emotions (Henry et al, 2017). Independently these tools cannot provide a comprehensive QoL assessment, but they provide a useful framework for selecting domains to include when assessing QoL in older horses.

QoL assessment undertaken by a veterinary surgeon is likely to be the most practical option, typically requiring less time and effort to complete than owner questionnaires. However, a veterinary examination is unlikely to result in a comprehensive, reliable assessment of the horse's QoL in its normal environment, performing a full range of activities. Owners have a long-term perspective and considerably greater knowledge of their horse's history and normal daily activities, and more awareness of how these matter from the horse's perspective (Yeates and Main, 2009). Therefore, owners are potentially better placed to assess the horse's mental wellbeing, making them useful proxies for QoL assessment.

Together with a thorough veterinary examination, asking owners to identify QoL domains that they consider to be important for their older horse could be a useful and practical way to inform a tailored assessment for rating and monitoring QoL in that individual. Using these owner-reported factors to design a small series of single-item questions could provide a valid, rapid assessment of QoL, which is feasible to use in a clinical setting (McGowan and Ireland, 2016; Figure 3).

Value of assessing quality of life

Formal QoL assessment in older horses has an array of benefits. Including owners in assessment of their horse's QoL can increase their level of reflection, encouraging them to consider the impact of management, healthcare and health problems. It can facilitate communication around geriatric health concerns, such as weight management or provision of analgesia, and allow owners to identify problems or possible improvements (Yeates and Main, 2009).

QoL evaluations can help inform management and treatment options, and can help to prioritise therapeutic interventions where animals have multiple concurrent conditions. It plays a major role in owner decision making, with owners of geriatric horses ranking QoL following treatment as the most important factor when considering potential treatment options for a severe illness or injury (Ireland et al, 2011c). QoL assessment can also be used in evaluating response to treatment, where it may be a more important measure of success than prolongation of life. Decreased scores for QoL measures may also help to identify detrimental side effects of treatment.

QoL ratings can be useful prognostic indicators: QoL has been reported to be highly predictive of outcome in human geriatric patients with conditions such as myeloid leukaemia (Deschler et al, 2013). Several QoL factors were associated with increased risk of mortality in geriatric horses (Ireland et al, 2011c). QoL assessment plays a vital role in decision making for euthanasia, as compromised QoL is a primary reason for equine euthanasia (Preshaw et al, 2018). Poor QoL was reported to be a major factor in euthanasia decisions for geriatric horses by 34% of owners, particularly for horses with lameness or chronic diseases where veterinary advice was less frequently identified as influential in the decision-making process compared with other health problems such as colic and acute injury (Ireland et al, 2011d). Having a measurable way of demonstrating that QoL is compromised may help to reduce owner distress (McGowan et al, 2012) or feelings of guilt surrounding this difficult decision.

Conclusions

Older horses may have different welfare issues and factors influencing their QoL than younger animals. Currently, there is no validated instrument for assessing equine QoL, in animals of any age. However, there is a wealth of resources from human and small animal medicine to help inform what domains should be included in QoL assessment for older horses. Veterinary surgeons should be proactive in discussing QoL with owners, and a comprehensive assessment of QoL in older horses should involve both the owner/carer and the veterinary surgeon. QoL assessment including evaluation of health-related factors, activities of daily living and mental wellbeing is beneficial for informing decision making regarding management, healthcare and euthanasia.

KEY POINTS

• Quality of life assessment in older horses should be a ‘team effort’, involving both veterinary and owner/carer appraisal.
• Although a validated equine quality of life assessment tool is not currently available, there is a wealth of available resources from human and small animal medicine, as well as several equine welfare assessment tools and pain scales, which can be used to inform quality of life evaluation in older horses.
• Multimorbidity is common in older horses, resulting in poorer health-related quality of life, but activities of daily living are also important factors to consider in any assessment, ideally tailored to the individual animal.
• Quality of life ratings can inform management and treatment decisions and provide a useful outcome measure of response to therapeutic interventions.
• Poor quality of life ratings are predictive for mortality in older horses, and having a measurable way to demonstrate compromised quality of life can aid decision making around euthanasia.