🤒 Sickness + Productivity

Physical Health – Animal Welfare Assessment

Physical Health & Disease
 Includes neuroendocrine, cardiovascular, musculoskeletal, metabolic, and immune responses

Stressors
 Caused by aetiological (etiology) agents such as trauma, toxins, etc.

Sensory Input
 Contributes to detection and response to environmental and internal stressors

Physical Health & Disease – Key Points

Animal Preferences vs. Health
 We need to consider both what animals want and what is good for their health

Welfare Assessment
 Must account for factors that reduce disease, deformity, and injury
 Also considers what promotes positive health, good growth, and longevity

Consideration
 What animals choose or work for is not always beneficial for their long-term health and welfare

Disease – Definition

General Definition
 Any deviation from or interruption of the normal structure or function of a part, organ, or system of the body
 Manifests as a characteristic set of symptoms and signs
 Etiology, pathology, and prognosis may be known or unknown

Expanded View
 Disease is not just illness or sickness
 Includes any departure from normal form (lesions) and function, whether clinically apparent or not

Causes of Disease / Cell Injury – Examples

Oxygen Deficiency
 One of the most common causes of cell injury and death
 Can result from heart failure, respiratory failure, etc.

Physical Agents
 Trauma, extreme heat or cold
 Damage cells and blood supply, alter nerve and muscle conduction

Infectious Agents
 Viruses (including intracellular parasites), bacterial infections, etc.

Nutritional Deficiencies and Imbalances
 Lack of essential nutrients or improper dietary balance

Genetic Derangement
 Inherited or spontaneous genetic abnormalities

Chemicals, Drugs, and Toxins
 Exposure to harmful substances

Immunological Dysfunction
 Immune system malfunction causing disease

Aging
 Natural degenerative processes over time

Workload
 Excessive physical or metabolic demand contributing to injury

Physical Health & Disease – Behavioural Adaptations

Behavioural Adaptation to Disease
 Animals often modify their behaviour to cope with disease
 Selective pressure from disease has shaped the evolution of behaviour

Physiological and Behavioural Responses
 Behaviour, adrenal, and other physiological responses help animals cope with disease (Broom, 2006)
 Behavioural changes are often key indicators for veterinary diagnosis (Broom, 1987)

Example
 A dog arching its back indicates abdominal pain

Effects of Disease
 Diseased animals may struggle to cope with their environment
 Often experience lower quality of life

Improving Welfare
 Veterinary treatment improves welfare by reducing negative effects of disease
 Diagnosis alone does not improve welfare—treatment is essential

Cytokines, Sickness Behaviour, and Depression – Overview

Triggering Events
 Infection or tissue damage (wounding) activates the immune system

Pro-inflammatory Cytokines
 Transmitted via neural and humoral pathways
 Signal to the brain to initiate sickness behaviour

Sickness Behaviour – Key Features
 1. Anorexia – reduced food intake
 2. Adipsia – reduced water intake
 3. Lethargy – low energy, inactivity
 4. Anhedonia – reduced pleasure or interest
 5. Hyperalgesia – increased sensitivity to pain
 6. Social withdrawal – reduced interaction with conspecifics
 7. Reduced grooming – neglect of self-maintenance
 8. Increased slow-wave sleep – more restorative sleep
 9. Impaired learning and memory – cognitive deficits
 10. Decreased libido – reduced reproductive drive

Motivational Model of Sickness

Threat
 Exposure to stressors

Fear Response
 Fear feelings – subjective emotional response
 Fear behavior – observable actions (e.g., withdrawal, avoidance)
 Visceral arousal – physiological changes preparing the body for threat (e.g., heart rate, respiration, hormone release)

Pathogenic Micro-organisms
 Exposure to pathogenic micro-organisms

Sickness Response
 Malaise – general feeling of unwellness
 Sickness behaviour – coordinated set of behaviours triggered by illness (e.g., lethargy, reduced appetite, social withdrawal)
 Visceral arousal – physiological changes accompanying sickness (e.g., inflammation, immune activation, altered metabolism)

Key Concept
 Sickness behaviour is part of a motivational system (goal-directed behavior), directing animals to conserve energy and cope with disease or infection

Benefits of Sickness Behaviour

Adaptive Strategy
 Sickness behaviour is an energy-saving response that helps the animal cope with illness or injury

Energy Conservation
 Decreased locomotion – less movement conserves energy
 Increased slow-wave sleep – promotes recovery and immune function
 Postural changes – positions that minimize energy use
 Reduced engagement in pleasurable activities (anhedonia) – avoids unnecessary energy expenditure
 Decreased social interactions and sexual behaviour – conserves energy and reduces risks

Physiological Compensation
 Helps offset high energetic costs of fever
 Conserves heat and allows tissue repair if injured

Ecological Benefit
 May reduce risk of predation even though vigilance is lowered

Key Concept
 Sickness behaviour coordinates physiological and behavioural responses to optimize survival and recovery

Sickness-Associated Anorexia

Functional Basis
 Anorexia during sickness may serve adaptive purposes related to infection and immune function

Five Hypotheses (Kyriazakis et al., 1998)
 1. Induction of the response for the parasite’s benefit
  - Parasite causes anorexia to help itself
 2. Reduced food intake starves parasite
  - Host eats less → parasite gets less nutrition
 3. Reduced energetic efficiency leads to anorexia
  - Infection reduces energy efficiency → host naturally eats less
 4. Anorexia enhances effective immune responses
  - Eating less helps immune system fight infection
 5. Anorexia leads to increased diet selectivity during infection
  - Host chooses more beneficial nutrients when intake is reduced

Issues / Evidence
 Hypotheses #1–3: inconsistent with observed physiological and behavioural changes during infection
 Hypotheses #4–5: supported by studies → anorexia likely adaptive

Key Concept
 Hypotheses #4 and #5 highlight that anorexia during sickness can improve immune effectiveness

Relationship Between Animal Welfare and Productivity 1

Historical Link
 Historically, there has been a strong connection between animal welfare and productivity (growth and reproduction)
 Improvements in housing, nutrition, and health management improved both welfare and productivity

Low Productivity as a Welfare Indicator
 Low productivity can indicate inadequate care, stress, or illness
 Energy that would normally support growth and reproduction is redirected to support the energetically costly immune response

Key Concept
 Optimizing welfare not only benefits the animal’s quality of life but also enhances productivity through better health and reduced stress

Relationship Between Animal Welfare and Productivity 2

High Productivity ≠ Good Welfare
 Increased productivity through genetic selection or intensive management can sometimes indicate poor welfare

Examples in Dairy Cows
 High milk production is associated with increased health problems, such as mastitis

Examples in Swine and Poultry
 Selection for high growth rates and production efficiency has led to health issues
  Skeletal problems and lameness are common in fast-growing chicken strains

Key Concept
 High productivity does not always reflect good welfare; intensive production can compromise animal health and quality of life

Relationship Between Animal Welfare and Productivity 3

Historical Link
 Historically, improvements in husbandry practices—such as housing, nutrition, and health management—led to both higher productivity and better animal welfare

Low Productivity
 May indicate inadequate care, stress, or illness
 Energy normally used for growth and reproduction is redirected to immune system activity

Key Concept
 While high productivity can reflect good management, it is not a guaranteed indicator of good welfare; context and underlying health effects must be considered

Animal Welfare & Productivity – Controversies

Inconsistent Relationship
 There is no consistent link between productivity and animal welfare

Conditional Indicator
 Measures of agricultural productivity can indicate welfare problems
  Only when low productivity is directly caused by inadequate nutrition, disease, or other stressors adversely affecting the animal

Key Point
 High or normal productivity does not automatically imply good welfare; careful interpretation is required