4.4 Life on the edge -> stress

What is a stressor?

Any environmental change that disrupts homeostasis and in which an animal percieves to be threatened

What is a stress response?

A suite of physiological and behavioural resonses that help to reestablish homeostasis

Kinds of stress

Acute

• fight-or-flight response

• alarm reaction, recovery follows quickly

• may save your life

Chronic

• constant/re[eated stress

• adjustments fail to compensate for stress

• ipairs immune response/general health

Stress response systems

There are 2 systems used by animals to help cope with stress:

1. Sympathetic-Adrenal-Medullary System (SAM) for acute stress

2. Hypothalamic-Pituitary-Adrenal System (HPA) for chronic stress

both use hypothalamus and get sent to adrenal gland

Pathway for SAM

Hypothalamus → nervous system signals from the brain (NS sender = acetylcholine) → adrenal gland → adrenaline

Pathway for HPA

Signal from hypothalamus → hormone excreted form pituitary gland (through blood) → adrenal gland → cortisol

Adrenal glands and stress hormones

adrenal glands are located on top. of kidneys

has cortex and medulla

Steps of stress response

1. perceive stimuli → visula, tactile, olfactory

2. autonomic response (SAM - alarm stage)

3. endocrine response to stress (HPA resistance stage)

4. exhaustion (after stress)

Autonomic respnse to stress

SAM - alarm stage

• adrenaline/epinephrine release

• increase responses/senses

• inhibit unnecessary functions

Endocrine Response to stress

HPA - resistance stage

• cortisol release

• glucose production, protein breakdown

Exhaustion (after the stress)

• body is at depleted state

• must rest in order to recover

• if stress continues without recovery → illness → DEATH

Stress factors for animals

social

feeding

management

poor health

environment

How do animals respond to stress

Physiological responses

• adrenaline

• cortisol

Behavioural responses

• active response → fight/flight

• passive response → hiding, abnormal behaviour, stereotypes

Examples of Behavioural Signs of Stress

vocalization

restlessness

fight/freeze

stereotypies (repetitive movement, posture)

Examples of Performance Signs of Stress

decrease in milk yield

decrease in feed intake and growth

decrease in body condition

decrease in fertility

increase in metabolic diseases

Examples of Physiological Signs of Stress

increased heart rate, blood pressure, respiration and skin temp

increase in adrenaline and cortisol

decrease in reproductive hormones

Examples of Immune Signs of Stress

presence of disease markers

decrease in white blood cells

increase in infectious diseases

Behavioural Assessments

• species-specific behaviours (have allowed animal to survive)

• learned behaviours

• animal preference tests

• dependent on many factors (ex. age, sex, health, density)

Hormonal Measurements

• stress will iincrease hormone (cortisol) seretion into blood

• from the bood, cortisol can move into other fluids or tissues so these can also be sampled to measure cortisol

• different strategies are used depending on the experimental situation

Measuring Cortisol - Blood (plasma)

regarded as the “gold standard”

measures total levesl of cortisol (free and bound hormone)

obtaining blood is stressful itself so draw as quickly as possible or use a catheter

Measuring Cortisol - Saliva

usually a linear relationship with free-cortisol in blood

can detect changes in cortisollevels within seconds to minutes (similar to blood)

can collect drool - far less invasive

Measuring Cortisol - Feces

• don’t have to even touch animal

• cortisol on blood goes to liver where it is metabolized and deposited into bile

• bile (with cortisol metabolites) is released into intestones and excreted in feces

• not as accurate as blood bc its gone through GI tract and liver

Measuring Cortisol - Urine

measures free cortisol levels (same as blood samples) - kidney filters out bound cortisol

sampling time needs to be kept consistent (circadian patterns in cortisol production)

can be difficult to collect

Measuring Cortisol - Hair

biomarker of chronic stress (humans, domestic and wild animals)

slow growth of hair means that the time scale is typically in weeks and months → near follicle (most recent) → near end (least recent)

advantages:

• can be cut or retrieved from environment w/o stress to animal

• can be transported w/o compromising sample