Dekker Encyclopedia of Animal Science.pdf

Adaptation and Stress: Animal State of Being

Stanley E. Curtis

University of Illinois, Urbana, Illinois, U.S.A.

INTRODUCTION

threat or actual shift in some internal or external feature, it

reacts to preempt or counteract that change. It attempts to

keep an internal steady state, and thereby to survive and

thrive. The essence of an animal’s homeokinetic mech-

anisms is similar to that of a home’s simple thermostat: a

negative-feedback control loop.

Sound animal husbandry depends on application of

scientific knowledge of many aspects of the biology of

the animals we keep. Environmental aspects of animal

care are based on application of principles of animal

ecology in design, operation, troubleshooting, and cor-

recting deficiencies. They are crucial to both economical

animal production and responsible animal stewardship.

Coping

ADAPTATION

An environmental adaptation refers to any behavioral,

functional, immune, or structural trait that favors an

animal’s fitness its ability to survive and reproduce

under given (especially adverse) conditions. When an

animal successfully keeps or regains control of its bodily

integrity and psychic stability, it is said to have coped.

A given stimulus complex provokes different responses

by different animals, and even by the same animal from

time to time. Tactics vary. Its response depends on the

individual’s inherent adaptability, accumulated life expe-

riences, current adaptation status, and current ability to

muster extraordinary responses.

Any environment has factors that threaten to overwhelm

its inhabitants. Animals are driven to adapt to their

environments, and thereby remain fit. Adaptation is an

animal’s adjustment to its environment, especially a

nonideal one, so its life and species can continue.

Realistic Expectations

Animals sometimes fail to adapt; they experience stresses

of various kinds. So they may feel well, fair, or ill

(described later). We should expect an animal to

experience well-being mostly, fair-being sometimes, ill-

being once in a while. When an animal shows signs of

failing to adapt, correcting the problem may not be easy.

STRESS

Failure to Adapt

Stress occurs when the stimulation an animal is ex-

periencing goes beyond that individual’s ability to adapt.

Environmental stress may ensue when the environ-

ment changes, adaptation status changes, or an animal

is moved to another environment. When an animal

has coped, its response is an adaptive response. But

there always are limits to adaptability. When attempts

to adapt fail, the response is a stress response, the stimu-

lus a stressor.

Failure to adapt stress has negative consequences

for animal state of being. Understanding untoward

consequences of such breakdowns for bodily integrity is

relatively clear-cut. But psychic disturbance or collapse

is often not even recognized. It is now believed that

humans can survive stress only to the extent we can cope

Animal Responses

An animal’s environment consists of a complex of

elements, each of which varies over time, across space,

in intensity. Most combine in additive fashion as they

affect an animal.

Internal steady state

An animal normally maintains steady states over time in

the various aspects of its internal environment. This

mechanism homeokinesis is the general basis of

environmental adaptation. When an animal perceives a

Encyclopedia of Animal Science

DOI: 10.1081/E EAS 120019427

Adaptation and Stress: Animal State of Being

psychologically. Likewise, Ian J. H. Duncan [1] thinks that

animal state of being has to do with animal feelings.

Measuring Impacts

COPING

Impacts of environmental impingements are estimated

by measuring their effects on the animal. The same

environment that would quickly chill to death a newborn

piglet might be well-tolerated by the sow. Differences in

thermal adaptabilities of the two put the same environ-

ment in the piglet’s cold zone, the sow’s neutral zone.

The numerous possible strategies and tactics for counter-

acting stimuli an animal usually has at its disposal imbue

flexibility and power to the animal’s adaptive responses

when it faces an adverse environment. But when an

animal responds to environmental stimuli, it is not

necessarily under stress or distress. Responding to stimuli

is a normal biological feat routinely carried out by every

normal, unstressed creature that lives. Typical scenarios of

environmental stimuli and animal responses run a wide

gamut. Modified versions of nine schemes created by

Donald M. Broom and Kenneth G. Johnson [2]

Tolerance Limits, Collapse, and Death

follow:

An animal ordinarily is confronted by more than one

stimulus at a time. Stimuli also impinge sequentially.

Animals in practical settings generally need to cope with

multiple stimuli.

A range of tolerance sets limits for an environmental

factors within which an animal can readily cope, thrive,

reproduce, survive i.e., experience wellness. Outside

this range are the upper and lower ranges of resistance. If

an animal resides long enough outside its tolerance range,

it eventually will die due to environmental stress.

1. In the face of stimuli, internal steady state is main-

tained with ordinary basal responses. State of being is

very well.

2. Complete adaptation achieved with minor extraordi-

nary response. Stimuli provoke adaptation. Fitness

and performance may be briefly compromised, but

wellness promptly returns.

3. Sometimes, animal response to stimuli over time is

neither extraordinary nor adequate. For so long as the

impingement continues, fitness and performance may

be reduced minor stress and fairness ensue but

after that, wellness returns.

4. Stimuli elicit some minor extraordinary response, but

over time this is inadequate for complete adaptation.

Both fitness and performance decrease awhile (fair-

ness), after which wellness returns. Stress is present at

scheme 4 and above.

5. An animal’s extraordinary response over a long period

achieves only incomplete adaptation. Although fitness

remains relatively high, performance is reduced. The

animal experiences overall fair-being.

6. To completely adapt, an animal sometimes must

mount an extreme response. During adaptation and

recovery periods, fitness and performance decline.

The animal is only fair.

7. Despite some extraordinary response to stimuli,

complete adaptation is not achieved long term. Fit-

ness and performance decline; the animal becomes

ill.

8. In some cases, an extreme response does not result in

complete adaptation even long term reducing the

ill animal’s fitness and performance.

9. An environmental stimulus may be so enormous and

swift that the animal succumbs before it can respond.

Kinds of Stress Response

There are four kinds of stress response. Some reduce an

animal’s state of being; others enhance it. Understress

occurs in simple environments that lack certain features

(social companions, play items) (stimulus underload).

Sometimes animals give behavioral signs of understress

(lethargy; exaggerated, repetitive activity apparently

devoid of purpose (stereotypy); some other disturbed

behavior). Eustress (good stress): situations of extraordi-

nary responses, but which the animal finds tolerable or

even enjoyable. Overstress: environmental situations that

provoke minor stress responses. Distress (bad stress):

circumstances that provoke major stress responses.

Judging from signs of negative emotions (anxiety, fear,

frustration, pain), distress causes an animal to suffer, but

to what extent is not yet known.

STATE OF BEING

An animal’s state of being is determined by any response

the environment requires and the extent to which the

animal is coping. When readily adapting, the animal is

well. When having some difficulty, it is fair. When frankly

unable to cope, it is ill. In reality, environments that make

animals ill are not uncommon. But it is our moral

responsibility to minimize such occasions and correct

them to the extent possible.

Adaptation and Stress: Animal State of Being

Scientific Assessment

mal’s top priorities. Other performance processes may not

be critical to an individual’s survival or reproduction, so

they are least protected and least spared.

When an animal responds to any stimulus, its main-

tenance needs invariably increase. Resource expenditures

in support of maintenance processes increase progressive-

ly along with stress intensity, so the animal’s potential

performance capabilities progressively decrease.

Our understanding of an animal’s state of being depends

on generally accepted observations, scientific laws and

theories, and unique individual experiences. In 1983,

Marian Stamp Dawkins and Ian J. H. Duncan believed that

the terms ‘‘well-being’’ and ‘‘suffering’’ would be very

difficult to define. [3] That remains the case two decades

later. Until more is known, it is unlikely that kept

animals will enjoy more of the objectively defined well-

being for which we all should hope. Following are some

questions to be asked in assessing animal state of

being. [4]

How Animal Responses Affect Performance

Is the animal

Environmental stimuli provoke an animal to respond,

which in turn can influence performance processes in five

ways. [5]

. Having its actual needs met, achieving internal

integrity and psychic stability, coping, adapting?

. Showing frank signs of sickness, injury, trauma,

emotional disturbance?

. As free of suffering as possible, experiencing mostly

neutral and positive emotional states?

. To some extent able to control its environment, predict

it, live harmoniously in it?

. Performing growing, reproducing, lactating, compet-

ing, working at a high level?

. Showing signs of imminent illness or being in a vul-

nerable state?

Responses:

1. Alter internal functions. As an unintentional conse-

quence, certain stress hormones secreted as part of

long-term adaptive or stress responses can reduce a

foal’s growth rate.

2. Divert nutrients from other maintenance processes

and performance. A nursling piglet that increases

metabolic rate simply to keep its body warm in a

chilly environment will have fewer nutrients left for

disease resistance and growth.

3. Directly reduce animal productivity. Thermoregulatory

responses to hot environments sometimes include

reducing internal heat production. Eggs laid by heat-

stressed hens weigh less than normal, due partly to

decreased feed intake, partly to a homeokinetic re-

duction in egg synthesis (which gives off heat).

4. Impair disease resistance. As a consequence, e.g.,

individual feedlot cattle under social stress due to

aggressive group mates are more likely to become

infected and diseased.

5. Increase variation in animal performance. Individual

animals differ in responses to stimuli and therefore

in performance even when residing in the same ad-

verse environment. Stress increases individual varia-

tion in performance.

Animal Needs

When an animal actually needs something it does not

have, it is experiencing a deficiency. At any moment, an

animal has specific needs based on its heredity; life

experiences; bodily, psychic, and environmental condi-

tions. Given its needs at a given point, then, the biological,

chemical, and physical elements of its environment

determine whether those needs are being fulfilled.

Functional Priorities Under Stress

A performing animal is one that is producing some

product, progeny, or work or performing some activity

useful to humans. The rate of performance of a

constitutionally fit animal usually is the best single

indicator of that animal’s state of being. [5] When its

performance wanes, the animal probably is not as well is it

could be.

When bodily resources become limiting as often

happens during stress some processes must be down-

played so others more vital at the moment can ascend. The

goals of individual survival (maintenance) and species

perpetuation (reproduction) in that order are an ani-

Other Considerations

Other environmental aspects of animal care include the

concepts of optimal stimulation, enrichment, predictabil-

ity, controllability, frustration, and helplessness. [6]

CONCLUSION

Foundations of success in environmental aspects of

animal care are the fundamental principles of animal

Adaptation and Stress: Animal State of Being

ecology and their application. Every situation is complex

and unique. There are no general recipes in these mat-

ters. The fundamental principles have been set forth here.

3. Duncan, I.J.H.; Dawkins, M.S. The Problem of Assessing

‘‘Well Being’’ and ‘‘Suffering’’ in Farm Animals. In

Indicators Relevant to Farm Animal Welfare; Smidt, D.,

Ed.; Martinus Nijhoff Publishers: Boston, 1983.

4. CAST. The Well being of Agricultural Animals; Curtis,

S.E., Ed.; Council on Agricultural Science and Technol

ogy: Ames, IA, 1997.

5. Curtis, S.E.; Widowski, T.M.; Johnson, R.W.; Dahl, G.E.;

McFarlane, J.M. Environmental Aspects of Animal Care;

Blackwell Publishing Professional: Ames, IA, 2005.

6. The Biology of Animal Stress: Basic Principles and

Implications for Animal Welfare; Moberg, G.P., Mench,

J.A., Eds.; CABI Publishers: New York, 2000.

REFERENCES

1. Duncan, I.J.H. Feelings of Animals. In Encyclopedia of

Animal Rights and Animal Welfare; Bekoff, M., Meaney,

C.A., Eds.; Greenwood Press: Westport, CT, 1998.

2. Broom, D.M.; Johnson, K.G. Stress and Animal Welfare;

Kluwer Academic Publishing: Amsterdam, 1993.

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