Why should you never tie horses close together at a trailer or hitchrail?

Tying horses in close proximity to one another is one of the most common and preventable causes of serious injury at boarding facilities, shows, and trail riding destinations, and understanding why it is dangerous helps horse owners develop the habit of maintaining adequate space between tied horses regardless of how well the horses appear to get along. Horses establish and maintain social hierarchies through physical interaction, and even horses that coexist peacefully in a pasture will assert dominance, express irritation, or react defensively when they are tied in close quarters with limited ability to move away from a threat. A horse that pins its ears, swings its head, or strikes at a neighboring horse creates a reaction in the second horse that is often violent and sudden — a cow kick, a strike, or a full swing of the hindquarters — and when both horses are tied with limited movement available, neither can escape the confrontation. The resulting injuries can range from bite wounds and kick injuries to broken halters, pulled-back horses, and entanglement in lead ropes that causes rope burns, cuts, and in serious cases broken legs. At a trailer, tied horses that get into a conflict can pull back simultaneously, damage the trailer, and create a dangerous loose horse situation in a busy parking area. At a hitchrail, a horse that spooks or pulls back while tied next to another horse can trigger a chain reaction that puts multiple horses and handlers at risk simultaneously. The minimum safe distance between tied horses is generally considered to be beyond the reach of each horse's head and hindquarters simultaneously — typically at least a full horse-length apart — so that even if one horse reacts, it cannot make contact with its neighbor. At shows and trail ride destinations where space is limited, using every available tie point along a trailer or rail to maximize the distance between horses is worth the extra effort. Horses that are known to be aggressive toward other horses should always be tied at the end of a rail or on the opposite side of a trailer from other horses, with maximum possible separation maintained at all times.