Optimal Methods of Documenting Analgesic Efficacy in Neonatal Piglets Undergoing Castration
Animal Ethics Pty. Ltd., Yarra Glen, VIC 3775, Australia
Department of Microbiology and Infectious Diseases, NSW Health Pathology, Nepean Hospital, Penrith, NSW 2750, Australia
Faculty of Medicine and Health, Nepean Clinical School, The University of Sydney Medical School, University of Sydney, Penrith, NSW 2750, Australia
Author to whom correspondence should be addressed.
Received: 27 July 2020 / Revised: 10 August 2020 / Accepted: 13 August 2020 / Published: 19 August 2020
Surgical castration in piglets is widely used in commercial pig production systems; however, it may cause pain and stress to the animal. There is an urgent need to develop effective pain-relieving medications to use for this procedure. Such products must meet high standards of proof confirming that they are effective. This requires undertaking trials to determine the duration and severity of pain that piglets experience during and after castration, and the extent of pain reduction in anaesthetic/analgesic treated piglets. Unfortunately, responses to pain may be transient, subtle, or variably expressed. Furthermore, there is no simple “gold standard” method to measure pain in neonatal piglets. Instead, researchers must rely on using a range of indirect measures of pain of varying reliability. Without understanding the nature of expression of piglet pain, and the reliability of test measures to detect it, there is the potential of misinterpreting trial outcomes. Although there is a high degree of variability in the literature of test methods employed and outcomes obtained, there is nevertheless a growing body of evidence to suggest that some piglet responses to pain induced by castration, are more consistently reproduced and specific to the pain experienced during castration than others. In this narrative review, we examine the potential indicators of pain in neonatal piglets undergoing castration to determine the optimal methods currently available to most accurately detect pain and assess pain mitigation.