Coding and quantification of a facial expression for pain in lambs

Area of Science:

• Veterinary Science
• Animal Behavior
• Pain Research

Background:

• Facial expressions are key indicators of pain in humans and are increasingly studied in animals.
• Developing reliable methods to assess animal pain is crucial for welfare and ethical treatment.
• Previous research has focused on facial grimace scales in various species, but a specific scale for lambs was lacking.

Purpose of the Study:

• To create and validate a Lamb Grimace Scale (LGS) for identifying pain-induced facial changes in lambs.
• To assess the reliability of the LGS in differentiating between painful and non-painful states in lambs.
• To investigate the impact of restraint on pain perception and facial action unit quantification in lambs.

Main Methods:

• Qualitative identification of facial feature changes in lambs experiencing pain from tail-docking.
• Development of the LGS comprising five facial action units: Orbital Tightening, Mouth Features, Nose Features, Cheek Flattening, and Ear Posture.
• Two experiments involving human observers scoring still images using the LGS, with quantitative analysis of facial action units and assessment of restraint effects.

Main Results:

• Human observers successfully used the LGS to differentiate tail-docked lambs from controls and pre- vs. post-docking.
• Significant increases in LGS scores were observed after tail-docking, correlating with other pain indicators.
• Restraint influenced observers' pain perception and quantitative measures of facial action units, with freely moving lambs showing lower LGS scores.

Conclusions:

• The Lamb Grimace Scale (LGS) is a promising tool for assessing pain in lambs through facial expression changes.
• Orbital tightening and mouth features are key quantifiable indicators of pain in lambs.
• Further research with larger sample sizes is recommended to confirm these preliminary findings and refine the LGS.