Part I: understanding pain in pigs—basic knowledge about pain assessment, measures and therapy

Table 2 Physiological parameters and biomarkers

Category	Physiological parameter/biomarker	References
Activity of the autonomous nervous system	Heart rate/heart rate variability Arterial blood pressure Respiratory rate Temperature (rectal, skin, eye)	[127, 133,134,135,136,137]
Hormonal concentrations in blood, saliva or urine	Adrenal axis: ACTH, cortisol	[138, 139]
	Sympathetic axis: adrenaline, noradrenaline, chromogranin a	[140,141,142]
	Neuropeptides (substance p, beta-endorphin)	[143, 144]
Blood energetic metabolites	Glucose Free fatty acids Lactate	[82, 133, 139]
Blood concentrations of inflammatory markers^*	Cytokines (interleukin-1, tumour necrosis factor-alpha) Acute phase proteins (serum amyloid a, c-reactive protein, haptoglobin, fibrinogen)	[42, 77, 143, 145, 146]
Enzymes	Creatine kinase Salivary α-amylase Total esterase activity and its components (lipase, cholinesterase etc.)	[127, 146, 147, 148]
Pterines	Neopterine Biopterine	[149, 150]
Proto-Oncogenes	c-Fos	[151, 152]

Physiological parameters and biomarkers that have been used for pain identification in pigs (adapted from [124] with exemplary studies for each category). * Inflammatory markers indicate the existence of an inflammatory state that may generate pain

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