When horse-to-horse companionship is not possible, cross-species companionship from goats, donkeys, or other animals can provide meaningful welfare benefits.
While horse-to-horse companionship is the ideal for meeting equine social needs, cross-species bonds can be genuinely meaningful and welfare-positive for horses that cannot be housed with conspecifics. The key welfare condition is that the relationship is mutually beneficial - the companion animal must also be safe and comfortable in the arrangement. Cross-species companionship should be viewed as a welfare mitigation strategy rather than an equivalent to natural social contact, but for horses in situations where horse companionship is impossible, the welfare benefit of appropriate cross-species bonds is real and significant.