Quality of life in animals

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Forum

During the past 3 decades, there has been a growing

interest in the concept of quality of life (QOL) as

it relates to human beings.1 As survival intervals for

human patients with incurable diseases have improved

and recognition of the potential undesirable effects of

treatment on a patient’s enjoyment of life has increased,

a gap has emerged between what can be achieved, from

the health provider’s perspective, and what should be

achieved, from the patient’s perspective. Traditional

measures of patient outcome—survival rate and dis-

ease-specific clinical measurements such as hemato-

logic variables—have increasingly been seen as incom-

plete,2 and the focus on mortality and morbidity in

health care has been steadily superseded by broader

considerations of QOL.3 A focus on QOL ensures that

the patient’s perspective is placed at the forefront of

decisions involving health care.

Quality of life considerations are central to virtual-

ly every aspect of the welfare and humane care of ani-

mals, particularly health care. Assessments of which

treatment to use, or whether to treat at all, and of treat-

ment efficacy all involve QOL considerations. The pre-

sent report was designed to present the justification, rel-

evance, necessity, and validity of QOL assessment in

animals; review the use of QOL assessments in veteri-

nary and pediatric human medicine; propose a defini-

tion and model for the concept of QOL in animals; and

suggest guidelines for clinical application of QOL

assessments in veterinary medicine.

Use of the Term “Quality Of Life”

in Veterinary Medicine

The National Library of Medicine’s MEDLINE

database and the Veterinary Information Network’s

information database were searched to examine cur-

rent use of the term “quality of life” in veterinary med-

icine. English-language articles related to clinical vet-

erinary medicine in which the term “quality of life”

was used in the title, abstract, or summary were

retrieved. Of the reports identified, 334-36 were random-

ly selected and reviewed.

All reports stated or implied that QOL was an

important factor in health care, but QOL was not

defined in any of the reports, and some investigators

used other terms interchangeably with QOL, implying

comparable meaning. All alternative terms referred to

health status and included free of significant clinical

signs,9 diminished clinical manifestations of disease,6

normal versus sick,34

and pain relief and improved

function of the patient.33

In 11 reports,4,5,7,19,21,26-29,34,36

owners or veterinarians were asked to rate the animal’s

QOL. Of these, only 134 provided criteria for the rating

system: excellent (normal), good (usually normal),

poor (usually sick), and very poor (always sick). Three

other reports5,28,29 provided rating systems without giv-

ing criteria for determining the ratings. In 1,28 QOL was

rated as very poor, poor, reasonable, good, or very

good. In the other 2,5,29 QOL was rated as excellent,

good, fair, or poor.

Quality of life was discussed as an objective in 4

reports.8,13,23,33 Improved QOL was referred to as “an

objective in the feeding and care of the older animal,”13

and as the objective in the diagnosis and management

of musculoskeletal problems.8 Quality of life was used

as an outcome measure to compare efficacy of 2 treat-

ments in 2 reports.7,34

Three reports5,21,28 discussed QOL as a factor con-

tributing to the decision for euthanasia of an animal. In

a study of dogs with congestive heart failure,21 poor

QOL was reported by 13% of pet owners to be the most

important factor in making the decision for euthanasia.

In a study of cats with cancer,5 all owners reported

using the animal’s QOL in their decision for euthana-

sia. In a study of medical management of dogs with

portosystemic shunts,28 the owner’s assessment of the

dog’s QOL was the most important factor affecting

their decision to request euthanasia.

This review of the literature suggested that current

usage of QOL in veterinary medicine can be summa-

rized as follows: the term QOL is being used but not

defined; authors typically assume that individuals

assessing QOL know what is meant and leave evalua-

tors to define the term in their own ways; criteria for

assessing or measuring QOL are rarely provided; QOL

is equated to health status, so that assessments of QOL

are assessments of health status; QOL is being used as

an outcome objective and to compare efficacy of treat-

ments; and QOL is being used to make decisions

regarding euthanasia of animals.

Defining Quality of Life

Quality of life is an enormously broad and com-

plex concept. The potential benefits of QOL assess-

ments are well accepted, yet there is no consensus con-

cerning its definition or the factors that affect it.37 Like

“happiness,” it is one of those terms that we all intu-

itively understand but which defies straightforward

From the VCA Robertson Boulevard Animal Hospital, 656 N.

Robertson Blvd, Los Angeles, CA 90069.

Quality of life in animals

Franklin D. McMillan, DVM, DACVIM

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and succinct description.38 There are a number of mod-

els of QOL, but they differ substantially in regard to the

structure of the concept.39 In the absence of a well-

accepted operational definition, investigators have

approached the subject by identifying the particular

components (usually called “domains”) that are to be

included and measured.40

In everyday language, as well as in the scientific,

psychological, and philosophical literature, several

terms are used in the evaluation of the subjective

nature of an individual’s life.41 Quality of life is closely

related, and may be equivalent, to a number of other

concepts, such as well-being42-44 (sometimes specified

as subjective,44-46 emotional,44,45 psychological,47 or men-

tal47 well-being), welfare,41 happiness,42,47 life satisfac-

tion,43,44,46 and contentment.47

Features of Quality of Life

Subjective experience—Quality of life refers to a

state of mind; it is a conscious, subjective, mental

experience. Regardless of how the components of and

conditions for QOL are analyzed or categorized, and

regardless of whether the contributing factors are from

physical or emotional origins, QOL can have meaning

only when it is understood to be a conscious mental

experience.

Role of affect—Affect (subjective feelings) plays a

preeminent and, I propose, exclusive role in all inter-

pretations of QOL in animals. For sentient animals,

emotions appear to be a relatively constant experience.

Human and nonhuman animals seem to experience

affect, to some extent, during virtually all of their wak-

ing life, and all affect seems to have a hedonic quality

(ie, it is either pleasant or unpleasant). Therefore,

affect contributes pleasantness or unpleasantness on a

continual basis to personal experience.45 When people

evaluate their well-being, the ratio of their affective

pleasantness to unpleasantness over time plays a cen-

tral role, and studies show that emotional pleasantness

is one of the strongest predictors of life satisfaction.45 It

follows, then, that a definition of QOL will include the

concept of emotional pleasantness. Specifically, better

QOL refers to a preponderance of pleasant rather than

unpleasant affect in one’s life over time.45,48

Affect appears to play such a central role in QOL

that it can be regarded to be the single common

denominator for all factors that influence QOL. That is,

it is through affect that anything influences QOL, and

any factor that does not have an influence on affect is

not relevant to QOL. For instance, illness impacts QOL

because of its associated feelings of discomfort.49

Physical impairments and disabilities may impact QOL

if they have an effect on feelings of comfort and plea-

sure, but if neither comfort nor pleasure is affected,

then these physical impairments or disabilities do not

impact QOL.

An important aspect of affect as it relates to QOL

is that affect is a continuum. Feelings vary on a wide

range from pleasant to unpleasant, and QOL, a func-

tion of affective states, likewise varies along a continu-

um. Because affect varies not only between individuals,

but also in the same individual over time and under

different circumstances, there are no clear-cut demar-

cations or recognizable cutoff points on the continu-

um, above which QOL is “satisfactory” (or “accept-

able,” “reasonable,” or “good”) or below which QOL is

“unacceptable.”

The individual nature of quality of life—In peo-

ple, QOL is determined by the nature of the individ-

ual’s experiences and by the values and meaning that

the person attaches to those experiences.50 Individual

preferences, values, and needs, which derive from the

individual’s unique genetic make-up and learned expe-

riences, lead each individual to assign different values

and priorities to different aspects of life. For example,

one individual may value social companionship over

physical health, whereas another individual may have

the opposite values. These priorities of value and pref-

erence will differ in important ways among individuals;

therefore, the components of QOL will have different

values to each animal or person.39

There is now a general consensus that QOL should

be assessed from the perspective of the individual,

incorporating that individual’s values and prefer-

ences.51 However, gaining insight into the perspective

of the patient is not always straightforward. In human

pediatric medicine, it is often very difficult to achieve

an accurate understanding of the perspective of the

child or to determine which dimensions of health are

most important and how the child values individual

matters.1 In veterinary medicine, the problem is monu-

mentally more complex, because the patients are of

another species. Nevertheless, the principle of assess-

ing QOL from the viewpoint of the patient remains the

goal. Fortunately, innovative research methods are pro-

viding new insights into animals’ personal preferences

and values.52,53

General Concepts

Comfort and discomfort—Central to the subjec-

tive nature of QOL is the array of affective states com-

prising comfort and discomfort. These states constitute

a continuum of feeling, ranging from comfort to

extreme discomfort (Fig 1). The comfort-discomfort

continuum comprises a major part of the emotional

pleasantness and unpleasantness that contribute to

QOL. The term comfort relates to the experiential

mental state of ease and peaceful contentment with no

(or minimal) discomforts.54 Discomfort, on the other

Figure 1—Illustration of the 2 domain model of quality of life in

animals.

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hand, relates to any unpleasant or disagreeable feeling,

or any negative affect. Sources of discomfort may be of

physical (eg, thirst, hunger, disease, nausea, full uri-

nary bladder, pruritis, temperature extremes, and pain)

or emotional (eg, fear, anxiety, loneliness, grief, frus-

tration, and boredom) origin. Suffering refers to dis-

comfort of extreme or prolonged intensity.43

Needs—Needs constitute a fundamental compo-

nent of an individual’s QOL. In fact, needs have been

considered so central to QOL that some investigators

have proposed QOL models in which needs are the

basic foundation. These needs models posit that for

people, QOL is highest when all, or most, of a person’s

needs are met and becomes progressively lower as

fewer needs are met.39 In animals, fulfillment of funda-

mental needs has been recognized as an important

aspect of well-being. Dresser55 has suggested that well-

being in animals implies “that the individual’s physio-

logic, security, and behavioral needs are fulfilled.”

Needs are generally interpreted as requirements for

normal function; basic needs must be satisfied for an

animal to maintain a state of physical and psychological

homeostasis.42 Physical needs have been easier to iden-

tify than psychological needs,42 undoubtedly because of

the subjective nature of psychological needs. Hurnik56

has defined needs as the physiologic requirements of an

organism necessary for normal development and main-

tenance of good health and has categorized needs as

life-sustaining, health-sustaining, and comfort-sustain-

ing. Satisfaction of needs is not necessarily identical

with satisfaction of desires (wants).56 Desires are those

things that an individual prefers to have or to have hap-

pen but are not necessary for normal functioning.

Odendaal57 has suggested that basic needs must be ful-

filled for an animal to have an acceptable QOL.

Modifying previous definitions,53,56 we can say that

for an animal, a need is something that would result in

discomfort or a threat to an animal’s life or well-being

if it were unfulfilled. Needs satisfaction, therefore,

lessens discomfort or threats to well-being, thereby

assuming a prominent role in QOL. A desire (want) is

something that increases pleasure. Hence, an unful-

filled desire does not result in discomfort, and fulfill-

ment of all desires is not necessary for a high QOL;

however, fulfillment of a desire increases emotional

pleasantness, improving QOL.

Control—A large body of research involving

humans has demonstrated that of the factors that con-

tribute to QOL, one of the most important is a sense of

control.46,48 A sense of control over one’s life and cir-

cumstances is one of the most reliable predictors of

positive feelings of well-being in human beings.44

Control has also been shown to have an important

influence on emotional well-being and health of ani-

mals.58

Our understanding of how a sense of control con-

tributes to emotional well-being in animals derives

from research on the concept of learned helplessness.

Studies involving use of escapable and inescapable

electric shocks—wherein animals would or would not

have the control to escape from or turn off the shock—

has revealed the differential effects of control, and the

findings have consistently led to the conclusion that

controllability of aversive environmental stimuli is of

fundamental value to emotional well-being. Whereas

no psychological changes were detected in the animals

that had control over the shocks, the animals that were

subjected to repeated sessions of uncontrollable shocks

in time developed a mental state of learned helpless-

ness, in which the animals would simply stop all efforts

at escape, sitting passively when shocked. Helplessness

refers to the perception that one has no control over

one’s own environment,58 and is a debilitating emotion-

al condition.58 A depressed emotional state (learned

helplessness is often used as a model of human depres-

sion) will generalize to the entire life experience, and

an animal that has reverted to a state of learned help-

lessness becomes unable to cope with even simple and

routine tasks in life, such as competing for food or

avoiding social aggression.58 The emotional effects of

learned helplessness, resulting from lack of control,

contribute substantially to discomfort in the individ-

ual’s subjective experience.

A sense of control appears to be critically impor-

tant for comfort and a pleasant emotional state.

Conversely, a sense of an absence of control can result

in a substantial increase in unpleasant affect. In human

medical practice, provision of hope and a sense of con-

trol has been shown to be an important aspect of

patient care.38 Even when the effect on treatment or

survival is minimal, establishing a sense of control over

one’s own disease can have a substantial effect on the

way symptoms are experienced.38 Restoring a sense of

control to a patient’s life is now considered to be an

important goal in medical care.38

Social relationships—In social animals, social

emotions appear to have evolved to promote bonding,

affiliations, and relationships and to motivate reestab-

lishment of contact if individuals become separated.59

Regulated by endogenous opioids60

and oxytocin,61

social bonds appear to be associated with pleasant

affect, and separation and isolation with an unpleasant

affect. If social relationships are disrupted, severed, or

impaired, a number of unpleasant feelings are activat-

ed to motivate the animal to reestablish the social asso-

ciation. Disruption of the mother-infant bond in mam-

mals is associated with intense emotional responses in

the infant—termed separation anxiety or separation

distress—that promote reunion.62 Separation distress is

also experienced in mature animals when they become

separated from an individual (which need not be a con-

specific) to which they have established a social bond

or attachment.62

The strong affect associated with

social relationships has the potential to substantially

influence QOL.

Health—Health is likely the most extensively doc-

umented, best understood, and most widely accepted

factor contributing to QOL. It is for this reason that

QOL is often mistakenly equated with health status.

Disease has an impact on QOL in several ways. The

discomfort of disease63 contributes a powerful negative

affect to one’s overall subjective experience, and relief

of this discomfort is a primary reason people seek

health care.49

Physical impairments and disabilities

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associated with disease have the potential to induce

discomfort and limit one’s opportunities for experienc-

ing pleasurable, affective states, thereby negatively

affecting QOL.

Stress—A comprehensive discussion of the

immensely complex issue of stress is beyond the scope

of this report. In my view, stress contributes to QOL

only through its association with affective discomfort

states, such as fear, anxiety, pain, loneliness, and bore-

dom, and the classic physiologic stress response

involving activation of the hypothalamic-pituitary-

adrenal axis may or may not play a role in QOL. Any

stress reaction that operates below the level of con-

sciousness and does not directly or indirectly influence

the animal’s affect is not directly relevant to QOL.

However, stress may have indirect effects on QOL

through, for example, its adverse effects on somatic

health,64 which creates discomfort.

The most important aspect of stress as it pertains

to QOL appears to be the animal’s ability to respond to

demands of its environment and to cope effectively

with challenging and aversive stimuli. The ability to

cope appears to be the factor most correlated with the

impact of stress on emotional well-being47 and physical

health.58 The level of well-being of an animal may be

better reflected in how the animal copes with the stress

it experiences, than in how much stress it actually

encounters.47

Quality of Life Domains

Researchers generally agree that QOL is a multidi-

mensional experience.65,66 Accordingly, QOL is tradi-

tionally viewed as a compilation of certain domains

and dimensions.66 A domain is a particular focus of

attention, such as psychological or social function-

ing.40,65 A dimension is generally considered a compo-

nent of a domain. For example, the domain of physical

functioning might include dimensions of mobility and

strength.1

Although authors disagree on the specific domains

that comprise QOL, some core domains are included in

most measures of QOL.66 The 3 basic domains of QOL

that have been identified and are most consistently

included in discussions of human QOL are physical,

psychological, and social functioning.65 Various models

identify different core dimensions for these domains;

however, some models propose different domains and

dimensions. For instance, a QOL model developed for

people with mental retardation included 8 core dimen-

sions67; a model developed for children integrated the

physical, psychological, and social domains into 6 core

domains3; and a model developed for children with

cancer included 19 domains.68

The difficulties that have been encountered in

determining specific domains of QOL in humans are

greatly compounded when we consider QOL of non-

human animals. Because QOL in all sentient species

appears to depend on a preponderance of pleasant ver-

sus unpleasant feelings,45,48 and knowing that discom-

fort denotes all of the unpleasant feelings, it can be

concluded that the basic requirement for high QOL is

a relative freedom from discomforts. The comfort-dis-

comfort states are the affective experiences through

which many factors exert their influence on QOL. For

example, health disorders negatively impact QOL

through discomfort states associated with disease.63

Similarly, social isolation influences QOL through dis-

comfort states associated with social emotions, such as

loneliness. Therefore, I propose that affective comfort

and discomfort states comprise one of the basic com-

ponents of QOL.

However, comfort-discomfort states are only a por-

tion of the affective composition of QOL. All QOL

models developed for humans include pleasant experi-

ences as an important component. For humans and

animals, a life of comfort may be a contented and sat-

isfied life, but it is not necessarily reflective of optimal

QOL. As an example, consider 2 dogs with equal levels

of comfort, but one has, in addition, a rich array of

pleasant experiences such as frequent trips to the park,

lots of periods of play, many people to interact with,

and a variety of delicious foods to eat. There can be lit-

tle doubt as to which dog has the higher QOL; it is the

dog with comfort and pleasures.

A Two Domain Model of Quality of Life

in Animals

I propose that QOL in animals is comprised exclu-

sively of affect. Accordingly, it is through affect that

anything influences QOL; if something has no influ-

ence (direct or indirect, present or future) on affect,

then it is not relevant to QOL.

As a result, I believe that a 2 domain (comfort-dis-

comfort and pleasure) model can be developed to

describe QOL in animals (Fig 1). The 2 domains reflect

the primacy of affect and allow the major affects to be

grouped. The comfort-discomfort domain incorporates

the affective states of discomfort, which may be of

physical or emotional origin. Discomforts of physical

origin include such conditions as illness, pain, nausea,

pruritus, hypoxia, thirst, hunger, constipation, temper-

ature extremes, and the like. Discomforts of emotional

origin include fear, anxiety, boredom, frustration, lone-

liness, separation distress and anxiety, depression, and

hopelessness or helplessness. The pleasure domain

likewise consists of affective states that may be of phys-

ical or emotional origin. Pleasures of physical origin

include such things as physical contact and gustatory

pleasures. Pleasures of emotional origin include social

companionship and mental stimulation.

Definition of Quality of Life in Animals

On the basis of this 2 domain model of QOL in

animals, the following definition for QOL in animals is

proposed: Quality of life is a multidimensional, experi-

ential continuum. It comprises an array of affective

states, broadly classifiable as comfort-discomfort and

pleasure states. In general, the greater the pleasant and

lesser the unpleasant affects, the higher the QOL.

Quality of life is a uniquely individual experience and

should be measured from the perspective of the indi-

vidual.

Measurement of Quality of Life

Measurement of QOL has engendered great con-

troversy and debate in the human field, and there is no

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consensus as to the best method for assessing QOL.

The usual method of collecting QOL information is

through patient self-assessment questionnaires,69 but

because of its highly subjective nature, QOL remains

difficult to quantify.

Most often, QOL is measured through use of a sur-

vey instrument designed to obtain the desired data.40

The survey instrument may comprise a single question

such as “How do you rate your quality of life?” or may

contain multiple items that may or may not be catego-

rized into separate domains.40 A number of standard

instruments have been developed to measure QOL in

human beings. Most instruments are designed to gen-

erate a single aggregate score39; however, as logical as

these scores appear, their inherent meaning remains a

matter of debate.39

Objective and subjective measurement—

Measurement of QOL requires quantification of a sub-

jective phenomenon. Because of the inherent difficul-

ties of such an enterprise, many studies of QOL involv-

ing humans have been directed at the use of objective

indicators to reflect the subjective status of patients.70

Examples of objective criteria include activity level,

physical functioning, disease and physiologic indices,

appetite, and social support and interactions.

Subjective criteria involve the way an individual feels

about aspects of life (eg, health, companionship) and

life overall.

Instruments designed to measure objective criteria

have an appeal because of the greater ease of quantify-

ing the measured items. In contrast to subjective mea-

sures of QOL, objective measures are valuable because

they permit standardization and provide an established

anchor point that can be compared across studies.71 In

addition, for individuals who cannot offer meaningful

insight into their own subjective mental states, such as

human neonates and infants, the mentally disabled,

and animals, objective criteria are often relied on as

representative of the subjective states comprising QOL.

However, the relationship between objective and sub-

jective assessments has been examined in human stud-

ies,38,71 and results suggest that there is a discrepancy

between objective life status and subjective life satis-

faction for some individuals, necessitating that both

objective and subjective criteria be assessed when QOL

is investigated.

Proxy measurement—Measuring QOL from the

individual’s own perspective is problematic when

patients are incapable of providing first-hand informa-

tion regarding their subjective experience. Most often,

such individuals are neonates, infants, mentally disabled,

or severely ill. Researchers, not wanting to exclude such

individuals from QOL analyses, have devised instru-

ments to acquire QOL information from closely associat-

ed alternative sources, such as parents, spouses, partners,

caregivers, siblings, and health care providers. Such indi-

viduals are termed “proxy” informants. Because of lan-

guage barriers, subjective information concerning QOL

of nonhuman animals must, with few exceptions,52,53

come from sources other than the animal itself.

Accordingly, the issue of proxy measurement has impor-

tant implications for assessment of QOL in animals.

The necessity of relying on data from proxy infor-

mants raises the question of how accurate QOL assess-

ments from health care providers and other individuals

involved in a patient’s care are. The accuracy of proxy

ratings has been studied extensively in adolescent and

adult humans by comparing data from proxy infor-

mants with data from patients themselves.

The challenges associated with assessing QOL in

pediatric human patients are different from those asso-

ciated with assessing QOL in adult patients, and close-

ly parallel those faced in assessing QOL in animals.

Infants lack the cognitive and language abilities to con-

vey QOL information or express care preferences.3

Furthermore, infants and children often have very dif-

ferent priorities from their adult caregivers,37 which

greatly complicates proxy ratings of a child’s QOL,

because adult caregivers do not share the child’s men-

tal framework for interests, desires, and goals.66

Quality of life of neonatal surgical patients was

assessed by surgeons and nurses72; substantial variabil-

ity was found in proxy assessments, based on experi-

ence of the nurses and surgeons. Numerous studies

provide evidence to suggest that proxy responses by

parents correlate poorly with the perceptions of the

child they are representing.73,74 In an extensive review

of the literature on child QOL instruments, Pal3 report-

ed that proxies such as parents and teachers agreed

fairly well in reporting on child functioning, but that

low parent-child concordance was found in other QOL

domains, such as certain types of subjective feelings in

regard to illness and emotional states. Poor agreement

between children and parents on measures of private

experiences, such as emotions and subjective states,

regardless of whether the child is healthy or sick, is

well-documented.75

Measurement of Quality of Life

in Animals

Criteria for measuring QOL in animals are lacking.

Although little has been written about QOL in animals,

much has been written about concepts that appear to be

closely related to QOL, such as well-being,42-47 welfare,41

happiness,42,47 life satisfaction,43,44,46 and contentment.47

Because of the likely overlap of many of these concepts

with the concept of QOL, much of what has been pro-

posed regarding measurement of these concepts

appears relevant and applicable to the concept of QOL.

Specific assessment criteria have been categorized by

authors in various ways, and include behavioral fac-

tors47,76,77 (normal and abnormal behavior and prefer-

ence studies52,53), neurochemical and endocrine fac-

tors76-78 (eg, catecholamines, glucocorticoids, and oth-

ers), health status,47,78 physical functioning (disability78),

immune function,76-78

morphologic changes,76,78

and

brain imaging.76 The 2 domain QOL model is depen-

dent on affect. Therefore, assessment criteria, like the

QOL factors they are intended to measure, have value

only insofar as they are associated directly or indirectly

with affective states. Measurement criteria that are not

associated with affective states are not relevant to QOL

and, hence, play no role in assessing QOL.

The goal of measuring QOL in animals from the

perspective of the animals is not currently attainable.

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Important barriers pose immense challenges to under-

standing nonhuman minds; among them, language

barriers and the vast differences between species,

sexes, breeds, age groups, and individuals regarding

needs, preferences, values, and sources of discomfort

and pleasure. However, with innovative behavioral

research techniques (eg, preference testing,78 aversion

learning,52 and demand curve analysis53) providing a

window to subjective feelings, the private feelings of

animals appear to be increasingly accessible. For now,

however, development of a practical proxy instrument

offers the greatest hope for a useful method of measur-

ing QOL in animals. The ideal proxy instrument must

address all recognized sources of comfort-discomfort

and pleasure in its selection of items for evaluation and

must be able to gain information about the magnitude

of affective states. Assessment of QOL in animals

should ensure that criteria being used are relevant to

the animal’s QOL.

Clinical Application of Quality of Life

Measurement in Animals

In the absence of a valid instrument for measuring

QOL in animals, clinical application of QOL measure-

ments must currently be guided by general principles,

rather than a precise numeric score. It is reasonable to

propose that the paramount objective in animal care—

medical and nonmedical—is to maximize QOL.

According to the 2 domain model of QOL, this goal is

accomplished by the dual effort of minimizing discom-

forts and optimizing (not necessarily maximizing)

pleasures. Insofar as possible, all unpleasant and pleas-

ant affect must be assessed and factored into a com-

posite view of the animal’s overall affective status,

because it is this composite of affect that represents our

best view of QOL. Quality of life must be assessed with

the most information about the individual as possible

(personal needs, desires, preferences); preferably,

proxy evaluations would be provided by the person or

persons who have the greatest knowledge of the indi-

vidual animal’s preferences, personality, and nature.

The intuitive value of QOL argues for use of QOL

as an endpoint in animal health care. However, the

validity of QOL measurements has not been scientifi-

cally substantiated, and because of potential inaccura-

cies in proxy evaluations, particularly proxy evalua-

tions given by human caregivers for nonhuman ani-

mals, it would be prudent to exercise appropriate cau-

tions when using QOL assessments.

The potential value and applications of assess-

ments of QOL in animals are vast, and QOL measures

offer promising application in such diverse areas as

clinical medicine and in determining minimum stan-

dards for animal confinement and housing, breeding

practices (companion and food animal), intensive

farming, use of animals in entertainment, and labora-

tory research. Of particular value to animal welfare is

the application of QOL to instances of mistreatment,

neglect, and abuse. Because of its importance for ani-

mal well-being in general and in clinical medicine

specifically, QOL research warrants priority status. One

of the most important objectives for research into QOL

in animals is to determine factors related to affective

states of discomfort and pleasure in animals, to estab-

lish how those factors vary with species, breed, sex,

and age and among individuals, and to identify meth-

ods for measuring affective states in animals. In addi-

tion, it is necessary to develop and validate an instru-

ment for proxy assessment of QOL in animals and to

develop and validate an instrument for assessment of

QOL from the animal’s perspective. Quality of life

assessments should be included in clinical trials of

medical treatments, and strategies for maximizing

QOL should be identified. Some of these objectives will

be easier than others to attain. All present difficult

challenges, and a collaborative multidisciplinary

approach that uses veterinarians, ethologists, cognitive

scientists, comparative psychologists, animal scien-

tists, immunologists, neurobiologists, physiologists,

pathologists, and epidemiologists will be required.78 A

concerted effort to understand QOL offers the greatest

opportunity for the betterment of the lives of all ani-

mals that we care for.

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