Table 2 Example physiological indicators of animal welfare and their general response to stress

Catecholamines (e.g., epinephrine and norepinephrine)

Increased in response to acute exposure to stressors

Increase observed in response to immune challenge (e.g., infection or disease), handling, feed restriction, transport, physical activity, and lameness [49]

Glucocorticoids (e.g., cortisol and corticosterone)

Increased in response to acute exposure to physiological or psychological stressors

Normal/decreased in response to chronic exposure to physiological or psychological stressors

Increased cortisol concentrations in response to blood sampling, feeding, transport, handling, immune challenges, isolation and restraint, and exercise [50, 53,54,55]

Reproductive hormones (e.g., luteinizing hormone (LH), gonadotrophin-releasing hormone (GnRH))

LH concentration is suppressed during exposure to stressful events, can be increased by acute exposure to stressors and can be decreased during chronic exposure to stressors

Decreased or delayed LH surge in sheep and cattle in response to isolation, restraint, and transport [50]

Decreased GnRH in sheep in response to electric stimulation administered short and long term and hypoglycemia [56]

Increase risk of failing to ovulate or ovulate a low estrogenic follicle in dairy cattle with lameness [57]

Fatty acid intermediates (e.g., prostaglandins)

Increased during acute exposure to physiological stressors

Increased in lipogenic pathways while suppressing fatty acid oxidation in pigs in response to heat stress [58]

Increased prostaglandin in rats in response to restraint and cage-switch stress [59, 60]

Metabolic enzyme markers (e.g., glucose, lactate dehydrogenase, creatine kinase)

Increased during acute exposure to physiological or psychological stressors

Increased gamma-glutamyl transferase in cattle in response to feed and housing changes [61]

Inflammatory markers (e.g., serum amyloid A, C-reactive protein)

Increased during acute exposure to physiological or psychological stressors

Increased acute phase protein, cytokines, and serum amyloid A concentrations in cattle in response to feed and housing changes [61]

Increase in APP various species (including cats, dogs, poultry, horses, mice, sheep, pigs) in response to infectious and inflammatory disease, social stress, isolation, transport, tail biting, handling [62,63,64,65]

Immune system markers (e.g., total white blood cells, white blood cell type ratios, interleukins (Il-IB and IL-6), immunoglobulins (IgA), T-lymphocyte, cytokines)

Decreased during chronic exposure to physiological or psychological stressors

Decreased levels of IgA in piglets repeatedly confined in individual housing; rats exposed to an electric foot shock and psychological stress rats; and mice chronically restrained [66,67,68]

Increased levels of IL-1 and IL-10 in mice with chronic-stress induced depression [69, 70]

Dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEA-S)

Increased during both acute and chronic exposure to stressors

Increased DHEA concentrations in horses with chronic stress; cattle in response to overstocking and transportation; and pigs after surgical stress [71,72,73,74]

Increases DHEA:CORT ratios in pigs and cows in response to transport and novel environments [75]

Cardiovascular function (e.g., heart rate (HR), heart rate variability (HRV), blood pressure (BP))

Increased HR and decreased HRV during acute exposure to physiological or psychological stressors

Increased BP during chronic exposure to physiological or psychological stressors

HR and HRV changes have been correlated with behaviour and positive and negative stimulus in horses, pigs, cattle, sheep, and dogs [76,77,78,79,80,81]

Respiratory function (e.g., respiratory rate (RR))

Increased RR during acute exposure to physiological or psychological stressors

Increased RR in sheep and cattle in response to heat stress [82,83,84]

Increased RR in working dogs in response to physical activity after a competition [85]