Horses are obligate social animals that experience severe psychological distress when kept in isolation, with welfare science clearly demonstrating the harm of single-horse keeping.
Equine isolation causes genuine psychological suffering measurable through behaviour and stress hormones. Horses kept alone weave, crib-bite, and show stereotypic behaviour indicating chronic stress. Separated horses call continuously and show physiological panic responses. This is not merely a preference but a fundamental welfare need rooted in the herd social structure on which this species depends for survival and psychological security.