Animal pains. 1. Mechanisms

Abstract

Whether bred for commercial or experimental purposes, farm animals are subjected, throughout their lives, to potentially painful practices: interventions for convenience or for livestock care (e.g. castration, dehorning) or surgery (e.g. caesarian section, implantations of permanent catheters). The development of tools to assess pain experienced by the animals and of pharmacological treatment requires good knowledge of the mechanisms involved in the onset and modulation of pain. The objective of our review is to report knowledge obtained in recent years that have an interest for pain management in livestock animals. The knowledge presented is largely derived from studies conducted on rodents and applicable to farm animals. Our review consists of three complementary parts. The first part describes the various stages of development, transmission and sensory and emotional integration of nociceptive messages involved in the onset of pain. The second part describes the different types of modulation that can activate or inhibit the transmission of nociceptive signals. The third part describes the neurophysiological processes that accompany pain and that can modulate it (inflammation, activation of the autonomic nervous system and neuroendocrine system).