Horses kept alone without equine or other suitable companions experience significant psychological welfare harms, with appropriate companionship being a fundamental welfare requirement.
Social isolation causes genuine suffering in horses. Horses evolved to live in continuous social contact, and isolation deprives them of companionship that is a fundamental behavioral need. Lone horses show clear signs of psychological distress - increased stereotypic behaviors, heightened fear responses, and difficulty settling. Some horses in isolation develop profound anxious states that affect their welfare every hour of every day. The welfare case for providing appropriate social companionship to all horses is strong and the practical barriers are usually surmountable through donkey or goat companionship if equine companions are unavailable.