This is the first study to report proportional death rates for dogs by euthanasia versus unassisted in the population of animals under primary veterinary care in the UK. The study additionally reports on demographic and clinical factors associated with euthanasia. Much of the previous literature focused on risk factors for euthanasia in animals in shelters, particularly in the US, limiting the generalisability to the UK dog population under primary care 18–21. Instead, the current study included deaths in 29,163 dogs under primary care with the aim of getting a deeper understanding of the processes around the deaths of dogs in the wider owned dog population. The results showed that the majority of deaths in dogs involved euthanasia, with 26,676 (91.5%) dogs euthanased compared with 2,487 (8.5%) that died unassisted. It therefore provides novel insights in to the demographic and clinical factors associated with euthanasia and unassisted deaths, providing an evidence-base for veterinarians on the aspects influencing the euthanasia decision-making process in dogs. In turn, this will enable veterinarians to support owners through that decision-making process, and to provide information on what is likely to happen as the dog ages, or as conditions progress.
The results support the study hypothesis that the odds of euthanasia relative to unassisted deaths in dogs rises with aging. Increasing age was associated with an increased risk of euthanasia, with dogs aged ≥ 15 years at 5.92 times the odds of euthanasia compared with those < 6 years. Previous studies have cited “old age” as a major reason for euthanasia 22,23,31, although to the authors’ knowledge, this risk has not been quantified previously. Given that age is the greatest risk factor not only for the probability of death, but also for the majority of morbidities associated with mortality 32–35, the increased risk of euthanasia identified in aging dogs in the current study is not unsurprising. However, this finding does highlight the increasing importance of quality of life (QOL) and euthanasia decision-making discussions between veterinarians and owners as dogs age. Decision-making in older animals may be more likely to include euthanasia as an option, as has been reported in a previous study based on dogs and cats diagnosed with diabetes mellitus 36. Conversely, veterinarians may be more reluctant to agree to euthanasia for younger, treatable patients 15. Although euthanasia may be used to relieve animals from suffering, their health and welfare prior to this decision should still be considered and suffering minimised. It is of concern that in a previous study, 69% of dogs aged over 10 did not receive veterinary care during the 18 months leading up to euthanasia 37. Promoting the welfare of geriatric patients is of high priority, including palliative veterinary care where appropriate 38.
Disorders with greatest probability of euthanasia compared with an unassisted death (using neoplasia as the baseline) included: poor quality of life, undesirable behaviour and spinal cord disorder. Improved nutrition and healthcare have contributed to extended canine lifespans, therefore maintaining QOL is a growing concern in companion animal practice 39. QOL in pets has been defined as states of comfort or discomfort representing a combination of physical and non-physical factors 40,41. However, QOL is often assessed by owners and is somewhat subjective 39. More recently, QOL surveys have been developed to help optimize and standardize euthanasia decision-making in pets 39,42. Given that poor QOL was identified as a predominant risk factor for euthanasia (OR 16.28), the use of validated QOL surveys could be particularly useful for veterinary professionals and owners in recognising and managing functional decline as canine patients age 39. Additionally, guidelines produced by the animal hospice movement 43 may prove useful in assessing QOL and, in turn, predicting quality of death 9.
The current study identified undesirable behaviour as a significant risk factor for euthanasia (OR 11.36). Behavioural problems are considered an important factor in the euthanasia of dogs 3,44,45, with previous reports suggesting behavioural problems account for 2–39% of canine euthanasia in veterinary practices 22,46,47 and 50–70% in animal shelters 44,48. The current study identified undesirable behaviour as the fourth most common reason for euthanasia, accounting for 7.3% of euthanasia deaths. Both genetic and environmental factors influence behavioural development and there is growing evidence to suggest that educating owners about puppy-raising practices, and the provision of ongoing socialisation and habituation, can reduce the incidence of problem behaviour 49. Steps to reduce the incidence of problem behaviours may not only improve the welfare of individual dogs (if problems are associated negative emotional states and/or inappropriate punishment from caregivers), but may also reduce the number of dogs euthanased due to behavioural issues. It might therefore be apt for veterinary professionals to prioritise behavioural discussions at initial puppy consultations. Veterinary practitioners often lack confidence in dealing with behavioural problems, which has been attributed to poor coverage of the subject in veterinary education 50. The current study findings support the suggestion for improved provision of behaviour medicine in veterinary education 50. It should be noted that very few dogs with an undesirable behaviour will die naturally, reflected in the finding that only 7 dogs in the current study died unassisted of an undesirable behaviour compared with 1679 dogs that were euthanased. Therefore, absolute values as well as the relative odds ratio should be considered when interpreting these results.
Spinal cord disorder was identified as a significant risk factor for euthanasia in the current study (OR 6.00). Disorders of the spinal cord include congenital defects, degenerative diseases, inflammatory and infectious diseases, tumours, injury and trauma and vascular diseases 51. Typical age at onset and presentation vary according to aetiology, but diagnosis of spinal cord disorders often involves advanced imaging such as computed tomography (CT) or magnetic resonance imaging (MRI) 51. CT and MRI scanning are complex and expensive procedures 52, therefore may not be accessible to all owners. If advanced imaging and possible subsequent surgery are required to treat a spinal cord disorder, it might be that an owner opts for euthanasia if the diagnostic and treatment options are not financially viable and there is not a realistic alternative to protect their dogs’ QOL. Such data were not available in the current study, but suggest an important area for future research.
The disorders with lowest odds of euthanasia (and therefore the highest odds of unassisted death) were traumatic injury, disorder not recorded, complication associated with clinical care and heart disease. Traumatic injuries are a common emergency presentation 53, with a US study reporting prevalence of traumatic injury at two large university veterinary hospitals as approximately 13% 54. The most common causes of trauma in the US study were motor vehicle accident (53.2%), unknown cause (12.2%) and animal interaction (11.1%) 54. The current study included deaths that occurred within or external to a veterinary practice, which may in part account for why euthanasia risk was lower in these dogs (and hence risk of unassisted death higher) as many dogs may have died at the time of injury, during transport or on arrival to a veterinary practice or at home.
Dogs without a cause of death recorded had reduced odds of euthanasia (OR 0.08) compared with neoplasia. Since euthanasia must be performed by a veterinary surgeon, or by a person who has been authorised to do so by a veterinary surgeon 55, it follows that euthanased dogs are more likely to have a disorder diagnosis prior to or on presentation for euthanasia. Bereaved pet owners report that they wanted to explore all possible treatment options before considering euthanasia 56. Dogs that died unassisted may have died at home, at an emergency out of hours clinic or may not have visited a veterinary clinic for a specific problem prior to death and hence might not have a disorder diagnosis.
Complications associated with clinical care in dogs resulted in reduced odds of euthanasia (OR 0.08) compared with neoplasia. The prevalence, however, was relatively low with 0.2% dogs euthanased and 2.1% dogs dying unassisted due to complications. This highlights the value of considering both the absolute (prevalence) as well as the relative (odds) values when interpreting epidemiological results. “Complications” may have encompassed a range of specific factors, therefore future studies may help evaluate this finding further to determine if there are specific complications more likely to result in euthanasia or unassisted death and whether there are preventative measures that could be implemented, such as those designed to reduce postoperative complications in elderly human patients 57,58.
Heart disease as a cause of death showed reduced odds of death by euthanasia (OR 0.14). There were 4.6% (1,047) euthanasia cases attributed to heart disease compared with 19.7% (251) unassisted deaths. Cardiac disease is often subclinical, non-fatal or chronic 59, therefore it may be that a proportion of the euthanased dogs died with heart disease (whether diagnosed or undiagnosed) rather than this being the definitive reason for euthanasia. Heart disease was the most common cause of unassisted death in dogs, highlighting management of this condition as important for veterinarians to discuss with owners of affected dogs. For example, one important area for such discussions may be the impact of breathlessness on quality of life; this clinical symptom is reported as having a profound impact on quality of life in human patients 60.
After accounting for other confounding factors such as grouped-level disorder and age, Rottweilers were more likely to be euthanased (OR 1.76) than to die an unassisted death, compared with Labrador Retrievers, whilst seven breeds were more likely to die from unassisted deaths including Bulldog, Pug, Cavalier King Charles Spaniel and Yorkshire Terrier. The reasons for the breed risks identified are likely multifactorial, with possible differences including the risk of sudden death between breeds, that would preclude euthanasia. Heart disease has previously been identified as the most common cause of sudden and unexpected death in dogs 61. In a recent VetCompass study, Yorkshire Terriers and Cavalier King Charles Spaniels had a significantly increased odds of degenerative mitral valve disease diagnosis compared with crossbred dogs 62, a cardiac disorder where 50% of disorder-related deaths are considered ‘sudden’ 63.
Cause of death terms were taken in to account in the multivariable modelling, therefore the differences in breed risks identified may result from other factors that the model could not account for. Such factors might include owner characteristics e.g. attitudes towards pet death, and the dog-owner relationship. The finding that brachycephalic breeds including the Bulldog and Pug were at increased risk of unassisted death is of interest, given their current boom in popularity 64. Although further research is needed, results of recent studies exploring the ownership behaviours and beliefs of owners of brachycephalic breeds may indicate that owning this breed type has the potential to influence when, and if, a dog is euthanased. Owners of brachycephalic breeds (specifically Bulldogs, Pugs and French Bulldogs) have been reported to form particularly strong dog-owner relationships 65. Although previous studies have found strength of the dog-owner bond is related to health-seeking behaviours in dog owners (e.g. owners with strong bonds seeking higher levels of veterinary care and being more likely to follow veterinary recommendations regardless of cost) 66, research on brachycephalic dog owners reveals disparities in their perceptions of dog health versus those of veterinary professionals; these differences may disrupt tendency to follow veterinary advice that is shown by owners of dogs in general. Owners of brachycephalic breeds tend to ‘normalise’ poor health in their breed. Although they may be aware that their dog is showing signs of respiratory disease, for example, they may not consciously accept that this is real problem for their dog, and instead attribute it as a ‘normal’ feature of their breed 67. This phenomenon has been found to extend beyond wakeful respiratory dysfunction, and to also cover dysfunctional sleeping, thermoregulation and eating that are normalised in these breeds, such that dogs need to reach a critical level of clinical severity before owners consciously acknowledge their dog has a ‘problem’ 65. These normalisation and thresholding phenomena may affect euthanasia-decision making, whereby owners may fail to perceive their dog as ‘unwell’ and do not consider their dog’s quality of life as sufficiently impaired to justify euthanasia. Consequently, some severely affected dogs are more likely to die an unassisted death.
The aforementioned strength of the owner-dog relationship in brachycephalic breeds may reduce the likelihood of euthanasia in other ways also. The strength of the attachment bond to a pet has been demonstrated to be a significant predictor of the severity of grief after the loss of a pet 68–70. Anticipation of this loss may delay or prevent owners in making euthanasia decisions 71. This effect may be exacerbated by the inherent morphology of brachycephalic breeds. The baby schema effect (the caregiving response precipitated by the baby-like facial conformation of animals including brachycephalic dogs 72) may modify brachycephalic dogs’ role as a ‘pet’ into a more child-like role, by triggering and enhancing a caregiver-infant-like relationship in these breeds 73,74. By seeing their pets as friends or family members rather than possessions, imposition of deaths may precipitate intense remorse in such highly bonded owners 75. The anthropomorphism of brachycephalic breeds 76, where human characteristics are conferred to dogs, could result in moral difficulties in owners contemplating euthanasia of their dog 77, and reduce the likelihood of owners making this decision.
Bodyweight was a significant predictor of death by euthanasia, with dogs 20 to < 30kg at 1.24 times the odds of euthanasia compared with dogs < 10kg. A previous study evaluating euthanasia or rehoming in dogs with behavioural issues reported an association between heavier bodyweight and increased risk of rehoming or euthanasia and/or the owners considering rehoming or euthanasia 78. The reasons behind this association were not discussed in detail, however there is a disproportionate risk of injury associated with larger and/or more physically powerful breeds, as well as the existence of breed stereotypes, which may have contributed to this previous association 79. Similarly, the precise reasons for differential euthanasia across weight categories in the current study are not clear. However, management considerations, such as the financial cost of treating larger dogs and difficulties in assisting with end of life care, might contribute to the association identified, although has not been previously explored.
A greater proportion of euthanased dogs were communally cremated (41.4%) compared with dogs that died unassisted (29.3%), whilst a greater proportion of dogs that died unassisted were individually cremated (64.5%) compared with euthanased dogs (52.9%). A similar proportion of euthanased dogs were buried (5.7%) compared with dogs that died unassisted (6.2%). In a previous study, Chur-Hansen et al (2011) found that owners needed memorials, such as an animal’s ashes, to help them move through the grieving process, with some owners stating it felt as if their animal was not completely gone 80. It is possible that owners whose dogs died unassisted may have desired to keep their dog’s remains (either through individual cremation or home burial) to aid in processing the grief of their loss. Conversely, owners of dogs who were euthanased may have benefited from a longer time processing the loss of their dog prior to their death, compared with those whose dog had an unassisted death, and therefore might not have felt as inclined to keep their dog in close proximity through home burial or retaining of ashes.
Decision-making about euthanasia involves the veterinarian and the animal owner(s). The veterinarian must shift focus from trying to cure the animal to admitting that there is nothing further that can be done, then convincing the client that the time has come for euthanasia 81. Animal owners, in turn, appreciate the support of a veterinarian when making the decision for euthanasia in cases where treatment options have been exhausted 56. The current study focuses on animal-related factors for euthanasia. However, client-related factors such as caregiver burden and financial constraints may lead to euthanasia decisions being made on grounds other than the animal’s quality of life and which could be the subject of future studies 82.
This study has many similar limitations to previous studies based on retrospective primary-care data 3. A large proportion of dogs that died unassisted did not have a cause of death reported (48.8%). Although a large proportion of this data were missing, dogs without a cause of death recorded were still included in the analysis to reduce bias. Some of the disorder groupings in the study might overlap, such as neoplasia and mass. The authors did not make any diagnostic assumptions i.e. disorders were recorded according to the attending veterinarian’s most specific diagnosis. Misclassification bias is possible in this instance, but may have been even greater if diagnoses are assumed. Euthanasia is a decision-making process involving owners, however the same cannot always be said for unassisted death and so this distinction should be accounted for when interpreting the results.