Horses are herd animals for whom social isolation causes acute and chronic stress. Understanding their social needs informs welfare-appropriate management decisions.
Horse social isolation causes welfare harm that extends across the full duration of the isolation period. An isolated horse in a stable without visual contact with other horses shows persistent elevated stress indicators - it is not an animal that habituates to solitude and becomes calm, but one that remains in a chronic stress state. Weaning foals abruptly from their dams causes acute distress in both animals that persists for days. The welfare compromise of isolated horse management is underappreciated because horses are often kept individually for management convenience, and their physiological and behavioral responses to isolation are not always obvious to owners who observe them only during handling. Social contact with at least one other horse should be considered a minimum welfare requirement.