Abstract
Many piglets are exposed to potentially painful husbandry procedures within the first week of life, including tail docking and castration, without the provision of either anesthesia or analgesia. The assessment methods used to evaluate pain experienced by piglets are often affected by low specificity and practical limitations, prompting the investigation of alternative methodologies. The assessment of changes in facial expression following a painful event has been successfully applied to several species. The objective of this pilot study was to evaluate the utility of a Grimace Scale applied to neonatal pigs to evaluate pain evoked by tail docking and castration. Eight female piglets, Sus scrofa domesticus (Landrace/Large White X synthetic sire line) underwent tail docking and 15 male piglets (75% Large White and 25% Belgian Landrace) were exposed to the castration procedure. Clear images of the faces of the piglets were collected immediately pre- and post-procedure. The images were used by experienced observers to identify facial action units (FAUs) which changed in individuals over this period, and a scoring scale was depicted in a training manual. A set of randomly selected images were then combined in a scorebook, which was evaluated after training by 30 scorers, blind to the treatment. The scale for most FAU was used with a high level of consistency across all observers. Tail docking induced a significant change (P < 0.05) in free moving piglets only in the “orbital tightening” FAU, whereas no change in any unit was observed in castrated piglets, which were restrained at the time of assessment. In this initial stage of development, orbital tightening seems to have the potential to be applied to investigate painful conditions in neonatal pigs. Nonetheless, more studies are needed to assess its full effectiveness and to evaluate the influence of possible confounds (e.g., handling stress) on the observed changes in FAUs.
Highlights
Many of the current methods of assessing potentially painful conditions in farm animals are limited by their sensitivity and subjectivity
“Orbital tightening” was the only FAU that significantly changed from pre- to post-tail docking (temporal tension: Z = −1.276, FIGURE 3 | Collection of images and explanations for each of the 10 facial action units (FAUs) included in the development of the Piglet Grimace Scale
The absence of a detected change in expression following castration highlights the possible confounds with other stressors associated with the procedure during measurement, and further studies should be carried out that avoid the limitations highlighted far
Summary
Many of the current methods of assessing potentially painful conditions in farm animals are limited by their sensitivity and subjectivity. In order to obtain more quantifiable measures of pain, techniques such as the recording of changes in spontaneous behaviors [4, 5] or in evoked nociceptive responses [e.g., Ref. [6,7,8]] have been adopted in a range of species These techniques may not necessarily provide sensitive and reliable indicators of pain [9,10,11,12] as they often have practical constraints, such as the need for extensive observation bouts or complex experimental set-ups [e.g., Ref. Due to the differences in pain perception associated with the early stages of maturation of the nervous system in humans [15, 16], it has been historically assumed that early-life injuries are not perceived as painful [17]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
