How facial expressions reveal acute pain in domestic animals with facial pain scales as a diagnostic tool.
Authors: Mota-Rojas Daniel, Whittaker Alexandra L, Coria-Avila Genaro A, Martínez-Burnes Julio, Mora-Medina Patricia, Domínguez-Oliva Adriana, Hernández-Avalos Ismael, Olmos-Hernández Adriana, Verduzco-Mendoza Antonio, Casas-Alvarado Alejandro, Grandin Temple
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Facial Expressions as Pain Indicators in Domestic Animals Recognising acute pain in animals remains clinically challenging, particularly in species that naturally suppress obvious pain behaviours; however, emerging evidence suggests that facial expressions offer a measurable, objective indicator of pain states across multiple species. This comprehensive review examines the neurobiological mechanisms underpinning pain-related facial changes—specifically how activation of the somatosensory cortex, prefrontal cortex, amygdala, hippocampus and hypothalamus triggers motor responses affecting facial musculature—and synthesises research on facial grimace scales developed for horses, cattle, pigs, sheep, donkeys, rabbits, rats, mice and cats. The authors argue that facial expression characterisation represents a significant advancement in pain assessment methodology, particularly valuable for farm animals, companion species and laboratory animals where traditional behavioural observation may miss early or subtle pain signals. For equine professionals, this framework is especially relevant: incorporating grimace scale assessment into routine examination protocols could enhance early detection of conditions ranging from dental disease and temporomandibular dysfunction to post-operative discomfort, potentially improving intervention timing and welfare outcomes. Farriers and veterinarians evaluating head-related pathology or pain would benefit from formalising facial expression assessment as a complementary diagnostic tool alongside traditional palpation and history-taking.
Read the full abstract on PubMed
Practical Takeaways
- •Use species-specific grimace scales (now available for horses, cattle, and other common species) as an objective, non-invasive tool to assess acute pain in your animals
- •Observe characteristic facial muscle changes (eye narrowing, ear position, nostril flaring, mouth tension) as reliable indicators of pain even in stoic animals that hide discomfort
- •Incorporate facial expression assessment into routine pain evaluation protocols alongside traditional behavioral and physiological indicators for more comprehensive pain management
Key Findings
- •Facial expressions change in response to painful stimuli across multiple species including horses, cattle, pigs, sheep, donkeys, rabbits, rats, mice, and cats
- •Grimace scales have been developed as validated diagnostic tools to improve pain assessment in veterinary medicine
- •Activation of somatosensory cortex, prefrontal cortex, amygdala, hippocampus, and hypothalamus with motor cortex connections elicit characteristic facial muscle movements during acute pain
- •Facial expression analysis provides a more sensitive method for pain evaluation in species that conceal pain behaviors or are difficult to assess clinically