Stress and animal health: All combined

Homeostasis

The process by which the internal environment of the body is maintained within parameters suitable for cell function, regardless of external changes.

What is the difference between health and welfare?

Health refers to the physical condition, while welfare includes both physical and mental well-being.

How can health and welfare be assessed scientifically and objectively?

Through:

• Physiological indicators

• Behavioral indicators

• Lab tests

• Structured observation

Allostasis

The changes in bodily functions that occur when the stress response is triggered that help the animal deal with the stressor

Fight-or-flight response

A physiological reaction in the animal in response to stressors in its environment

Walter Bradford Cannon

A physiologist who coined the terms 'fight-or-flight response' and 'homeostasis

How does short term and long term effects of allostasis differ?

• Short term

  • Helps an organism to protect themselves from dangerous stressors by changing the rates of bodily processes to allow the organism to defend against the threat, or to flee from it

• Long term

  • If an organism is under constant stress for long periods of time, the changes to bodily processes that occur can be harmful

What are the two major components involved in the stress response?

HPA-axis and SAM-axis.

Stressor

Any physical or psychological challenge that threatens homeostasis.

What types of stressors exist?

• Physical

  • Injury

  • Physical exertion

  • Noise

  • Overcrowding

  • Excessive heat or cold

• Psychological Stressors

  • Social conflict

  • Isolation

  • Traumatic life event

Allostatic load

The physiological cost of maintaining stability in changing environments.

Allostatic overload

A state where energy requirements exceed the capacity of the animal to adapt meaning it can no longer adapt, leading to poor welfare.

What factors contribute to allostatic load?

• Age

• Sex

• Personality

• Social position

• Early life history

Does absence of stress guarantee good health and welfare?

Not necessarily; welfare is multifaceted and includes positive experiences.

Quality of life

A concept referring to a life worth living and introduces the idea of considering welfare across the duration of the animal’s life and the need to assess quality of life.

How do we ensure good welfare?

By meeting physical and mental needs, monitoring behavior, and minimizing stress.

Why is behavior a good indicator of welfare?

It reflects the animal’s physical and mental state and can signal distress or well-being.

How can AI help in monitoring animal welfare?

By detecting, counting and tracking indivivduals in a flock

3Rs

Principles for ethical animal research: Replace, Reduce, Refine

What is the role of the brain in stress and welfare?

It perceives stressors and pleasures, and initiates physiological responses.

Sentience

The ability to feel, perceive and experience; central to the animal welfare debate.

Why is sentience important in welfare discussions?

It determines whether animals can suffer and experience emotions.

Which group of animals is often excluded from welfare discussions?

Invertebrates.

Why should we care about invertebrate welfare?

They show signs of intelligence, emotion, and personality

And are used in food, research, and as pets.

What percentage of animal species are invertebrates?

Over 95% of the earths animal species and 97% of living animals are invertebrates

Are invertebrates protected by welfare legislation?

Mostly not, except for all cephalopods in the EU.

Why does cephalopods make the legislagtion cut?

Because they can perform problem solving, use tools, they are capable of planning and they have personalities which are all hallmarks of the complex, flexible intelligence that we associate with vertebrate animals, mostly mammals

Applied ethology

The scientific study of animal behavior, with a focus on improving animal welfare, management, and human-animal interactions

What is the difference between ethology and applied ethology?

Ethology focuses on discovering and understanding natural behavior while applied ethology uses that understanding to improve animal lives and interactions with humans

The Five Domains Model

A welfare assessment framework used to evaluate animal well-being, distinct from the Five Freedoms

What effect does negative handling have on farm animals?

It increases fear and stress and reduces growth, feed efficiency, reproduction, and health

Rough handling

Includes shouting, hitting, approaching too quickly, or unpredictable movements that cause animals to associate fear with humans

How can human presence affect animals even without physical contact?

It can cause stress and avoidance behaviors, as seen in little penguins at Melbourne Zoo

What effect does human presence have on top predators like jaguars?

Increased aggression and pacing behavior, and more time spent out of sight

Can animals distinguish between individual humans?

Yes, but they often generalize fear from one handler to others

What evidence shows animals can differentiate between humans?

Imprinted chicks and goslings show preference for their handler; poultry react differently to different people

What factors affect human-animal interaction? AKE PAG

• Attitude

• Knowledge

• Experience

• Personality

• Anxiety levels

• Gender

How does experience affect animal response?

Extensive experience and species knowledge improve animal response, but long-term experience may lead to aversive behavior

How can human emotions, such as anxiety, affect animal behavior?

Animals can detect human emotional states through cues like body odor. For example, horses exposed to human “fear odors” show increased fear responses and reduced interaction compared to “joy” or control odors.

How can physical environment affect human-animal interaction?

It can either hinder or facilitate positive interactions depending on design

What zoo design features reduce animal stress?

Small, dispersed viewing areas and elevation differences between visitors and animals

How can keepers influence zoo animals' reactions to visitors?

Positive reinforcement training by keepers can reduce animals' stress responses to visitors

One Health

An integrated approach to optimize the health of people, animals, and ecosystems

What are the benefits of positive human-animal interactions?

They reduce animal fear, improve welfare, and can synchronize stress levels between humans and animals

What are potential solutions to reduce negative interactions?

• Increased contact

• Appropriate behavior

• Improved facilities

• Consistency in interactions

How can positive interactions serve as enrichment?

Additional caretaker contact increases affiliative behaviors and reduces abnormal behaviors in primates

What is the effect of frequent neutral interactions?

They can lead to habituation and reduced fear of humans

What is the most common form of human-animal interaction?

Pet ownership

Why is it important to consider pet quality of life?

To ensure the five freedoms and prevent abandonment

Zoonotic diseases

Diseases shared between animals and humans, posing health and economic risks

Reverse zoonosis

The transfer of pathogens from humans to animals, increasingly common due to urbanization and globalization

Hypothalamic–pituitary–adrenal axis (HPA axis)

A neuroendocrine system that regulates stress responses.

Glucocorticoids

Steroid hormones (e.g., cortisol, corticosterone) involved in glucose metabolism and synthesized in the adrenal cortex.

CORT

Short for cortisol and corticosterone, key glucocorticoids in stress response.

Glucocorticoid receptor (GR)

A receptor activated by high levels of CORT during stress.

Mineralocorticoid receptor (MR)

A receptor with high affinity for CORT, activated even at low concentrations.

Intracellular receptors

Receptors located inside cells that regulate gene transcription after binding hormones.

Negative feedback mechanism

A process where CORT regulates its own secretion via GR and MR activation.

Stress

Any stimulus that disrupts the body’s internal balance.

Immune suppression by CORT

CORT suppresses immune responses directly and indirectly.

Therapeutic use of CORT

Used to treat diseases involving inflammation, but long-term use has side effects.

Reproductive suppression by CORT

• CORT affects gonadal steroid synthesis and gonadotrophin secretion.

• Reduces testosterone and progesterone

• Leads to smaller yolk/egg mass

Circadian rhythm

Daily cycle of cortisol production, peaking in early morning and declining throughout the day.

Corticosteroid-binding globulin (CBG)

Main protein that carries glucocorticoids in blood and regulates free hormone levels.

Free hormone hypothesis

Only unbound hormones (not attached to CBG) are biologically active.

Radioimmunoassay (RIA)

Highly sensitive test using radioactive isotopes and antibodies to detect hormones.

What are the effects of CORT on stress response?

It activates the HPA axis and helps regulate behavioral and physiological responses.

In the short term it has beneficial effects by suppressing excessive immune responses.

In the long term they lead to allostatic overload and adverse health effects.

How do GR and MR differ in their activation by CORT and what happens when they bind to CORT?

MR is activated at low CORT levels, GR at high levels during stress. When they bind they translocate to the nucleus and regulate gene transcription.

How does stress affect homeostasis?

Stress disrupts homeostasis, leading to allostatic load.

What are the risks of long-term stress on immunity?

It increases susceptibility to disease.

How does CORT treatment affect chickens and goats?

It alters stress responses and physiological outcomes.

Why is circadian rhythm important for health?

It supports processes like cell repair and immune restoration.

How does age affect HPA axis sensitivity in chickens?

Sensitivity changes with age; testing same vs. different chicks matters for interpretation.

What role does CBG play in seasonal hormone variation in birds?

It regulates free CORT levels despite changes in total hormone levels.

Which individual differences affect HPA axis sensitivity?

Genetics, environment, and gene-environment interactions all play a role in affecting HPA-axis sensitivity.

Can plasma CORT levels indicate animal welfare?

Yes, increased CORT can reflect both stress and positive experiences.

What are the methods to measure CORT?

Blood, hair, feathers, saliva, and feces.

What analytical methods are used to measure CORT?

RIA and ELISA.

How does domestication affect HPA axis sensitivity in chickens?

It alters stress responses and adrenal gene expression.

What does brain size and composition reflect?

Processing power.

Why do we use brain size as a proxy for processing power?

Because larger brains are generally associated with greater cognitive abilities.

Domestication Syndrome

A set of traits including larger size, paler coloration, reduced fearfulness, and smaller brains in domesticated animals.

Spatial learning test

A test used to assess cognition in chickens by having them learn which alley leads to a food reward.

How does stress affect cognitive performance in chickens?

Chickens exposed to an unpredictable light schedule (stressed group) showed impaired cognitive performance compared to those raised under a normal 12:12 light-dark rhythm (control group).
Cognition was tested using a spatial learning test, where birds had to learn which alley led to a food reward.
Stressed chickens required more attempts to solve the task, indicating that stress negatively impacts learning ability.

What is direct brain measure?

Techniques that provide information about how animals perceive and respond to their environment, often difficult to perform without harm.

Examples of direct brain measures (EMP)

• Electrodes

• Postmortem brain measures

• MRI.

How do dogs' brains respond to human faces compared to everyday objects?

When dogs were shown pictures of human faces, brain activity increased significantly in several regions.
In contrast, no significant brain activity change occurred when they were shown everyday objects.

Brain lateralization

The specialization of the left and right brain hemispheres for different types of behavior and information processing.

What does the left hemisphere control?

Well-established behaviors in non-stressful situations.

What does the right hemisphere control?

Responses to unexpected stimuli and emergency behaviors.

How do cows respond to novel, fear-inducing stimuli?

They use the left eye, indicating fear.

What does left-eye preference in horses indicate?

Reactivity and coping style/personality.

Brain regression hypothesis

According to this hypothesis, domesticated (and therefore less fearful) animals adaptively reduce the brain size in order to reallocate energy and resources to traits such as reproduction. Believed to reflect the reduced functional needs of domesticated animal’s brains.

Are brain size and body size genetically constrained in chickens?

Brain size and body size are not strickly constrained =

Body size can increase in size without leading to the same increase in brain size

Cerebellum

The most neuron-dense brain region, involved in voluntary tasks and cognitive processing.

What are some cognitive abilities observed in chickens?

• Chickens show remarkable cognitive abilities such as:

  • Can do math and geometry

  • Memorize up to 100 human faces and recognize other chickens

  • Have unique personalities

  • Use logic and complex social tactics

  • Show self-control and can delay gratification

  • Possess an extensive vocal repertoire

How do the sympathetic and parasympathetic nervous systems influence heart rate variability (HRV)?

• The sympathetic nervous system (SNS) activates during stress, releasing norepinephrine, which increases heart rate and shortens intervals between beats.

• The parasympathetic nervous system (PNS) activates during relaxation, releasing acetylcholine, which slows heart rate and lengthens intervals between beats.

• In unstressed individuals, both systems are balanced, resulting in higher HRV.

• A decline in HRV indicates increased SNS activity and stress.

HRV reflects stress by analyzing the average heartbeat interval, the number of intervals, and their variability.

What happens in the body during an acute stress response?

1. Acute Stressor – A sudden event (e.g., slipping or facing an angry dog) triggers the stress response.

2. Amygdala Activation – The amygdala processes sensory signals and links them to emotions like fear or anger, sending distress signals to the hypothalamus.

3. Hypothalamus Alerted – Assesses the situation as threatening and activates the next steps.

4. Sympathetic Nervous System (SNS) – The hypothalamus activates the SNS, increasing heart rate and blood pressure, and stimulating the adrenal medulla.

5. Adrenal Medulla – Located in the adrenal glands near the kidneys, it releases adrenaline.

6. Adrenaline & Noradrenaline Released – These hormones boost oxygen and glucose supply, suppress non-essential functions (e.g., digestion), and increase physiological arousal.

7. Fight or Flight – The body is energized to either confront or escape the threat.

8. Physiological Reactions – Includes increased heart rate, blood pressure, and pupil dilation to prepare for physical action.

How does the SAM system respond to stress at the physiological level?

• The sympathetic nervous system sends signals via preganglionic nerve fibers to activate the adrenal medulla.

• Once activated, norepinephrine and epinephrine are released into the bloodstream by postganglionic nerve fibers.

• These hormones trigger the fight-or-flight response, preparing the body for immediate action.

What are the key physical signs of the fight-or-flight response and their functions?

• Rapid Heartbeat and Breathing – Increases oxygen and energy supply for quick reaction.

• Pale or Flushed Skin – Blood is redirected from the skin to muscles and vital organs; clotting ability increases.

• Dilated Pupils – Enhances vision and awareness of surroundings.

• Trembling – Muscles tense in preparation for action, causing shaking.