Physiological Indicators of Animal Welfare

Physiological indicators provide objective, measurable information about the internal state of an animal. They complement behavioural observations and help assess welfare in terms of stress, health, and well-being.

a. Heart Rate and Heart Rate Variability (HRV)

• Heart rate increases in response to stress, pain, or fear.
• Monitoring HRV gives insight into autonomic nervous system balance.
• Normal resting heart rate indicates a calm and comfortable animal.
• Example: Cattle show increased heart rate during handling or transport stress.

b. Respiratory Rate

• Elevated respiration can indicate pain, fear, heat stress, or disease.
• Slow, regular respiration suggests a relaxed state.
• Example: Pigs show rapid breathing when exposed to high temperatures or overcrowding.

c. Body Temperature

• Core temperature reflects metabolic status and stress response.
• Fever indicates infection; hypothermia may indicate environmental stress or illness.
• Example: Sheep in cold environments without shelter may show hypothermia, affecting welfare.

d. Hormonal Indicators (Stress Hormones)

• Cortisol: Primary stress hormone in mammals; elevated levels indicate acute or chronic stress.
• Catecholamines (adrenaline, noradrenaline): Rise during acute stress or fear.
• Prolactin: Can increase due to stress or altered reproductive states.
• Methods: Blood, saliva, urine, or fecal analysis.

e. Immune Function Indicators

• Stress and poor welfare can suppress immunity.

Measured through:

• White blood cell counts.
• Immunoglobulin levels.
• Disease susceptibility.
• Example: Chronically stressed poultry may show reduced antibody production.

f. Gastrointestinal Indicators

• Stress can alter digestive enzyme activity and gut motility.
• Diarrhea or reduced feed conversion efficiency indicates poor welfare.
• Example: Heat stress in pigs leads to gut dysfunction and reduced nutrient absorption.

g. Blood Biochemical Indicators

• Blood parameters reflect physiological stress:
• Glucose levels: Hyperglycemia under acute stress.
• Lactate: Elevated after strenuous activity or stress.
• Acute phase proteins: Indicate inflammation or tissue damage.

h. Reproductive Hormones and Performance

• Stress can suppress reproductive hormones, reducing fertility.
• Monitoring progesterone, estrogen, or testosterone can indicate welfare impacts.
• Example: Heat stress in cows reduces estrus behavior and conception rates.

i. Other Physiological Indicators

• Pupil dilation indicates fear or arousal.
• Sweat or salivation may increase under thermal or emotional stress.
• Heart and respiratory synchrony indicates relaxation versus stress states.