The Application of 3D Landmark-Based Geometric Morphometrics towards Refinement of the Piglet Grimace Scale

Maria E. Lou, Samantha T. Porter, Jason S. Massey, Beth Ventura, John Deen, Yuzhi Li

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Proper methods of assessment to objectively identify pain are essential for welfare improvements of piglets undergoing surgical castration on commercial farms. The Piglet Grimace Scale (PGS) is used to identify changes in facial expressions caused by acute pain in piglets undergoing tail docking and castration. However, subjective scoring methods are a concern for the validation of the PGS. The objectives of this study were to evaluate and refine the PGS through 3D landmark geometric morphometrics. Male piglets (n = 88) were randomly allocated to one of two treatments: castration and sham-castration. Piglet facial images were taken at four time points (before treatment, immediately post-treatment, 1 h post-treatment, and 4 h post-treatment) using a photogrammetry rig. Images were scored by four raters using five facial action units (FAUs): orbital tightening, ear position, temporal tension, lip contraction, and nose bulge/cheek tension. Three-dimensional facial models were generated and landmarked denoting 3 FAUs (orbital tightening, lip contraction, and nose bulge/cheek tension). Results suggest that orbital tightening and ear position may be reliable FAUs for the PGS. However, neither the PGS nor 3D landmark-based geometric morphometrics were able (both p > 0.10) to reliably identify facial indicators of pain in piglets undergoing castration.

Original languageEnglish (US)
Article number1944
Issue number15
StatePublished - Aug 2022

Bibliographical note

Funding Information:
This research was funded internally by the Minnesota Agriculture Experiment Station.

Publisher Copyright:
© 2022 by the authors.


  • animal welfare
  • castration
  • pain
  • photogrammetry

PubMed: MeSH publication types

  • Journal Article


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