Sheep are prey animals with strong behavioral masking of pain and illness, creating significant challenges for welfare assessment and ensuring that pain management reaches animals who need it.
Sheep welfare assessment is complicated by the evolutionary pressure that makes sheep hide pain — prey animals that signal weakness attract predators, so sheep have evolved strong behavioral suppression of pain indicators. This stoicism creates a welfare monitoring challenge: sheep who appear normal to casual observation may be experiencing significant chronic pain from lameness, dental disease, or internal parasitism. The development of facial pain assessment tools for sheep represents an important advance in penetrating this behavioral mask. Effective sheep welfare requires both validated assessment tools and observation frequency that detects the behavioral indicators that sheep do allow themselves to express.