Horses pose a unique challenge during transport due to their high-strung nature and tendency toward a flight response when alarmed. A horse should generally have its head restrained during trailering to prevent it from turning around inside the trailer, but it's very important that the horse can easily break free in case it becomes panicked. Several types of trailer ties are available commercially, each with its own advantages and disadvantages.
Safe Trailer Ties
The most common type of trailer tie is a nylon adjustable-length tie with a "panic snap" on one end. The panic snap allows the tie to be released with an easy downward motion if the horse pulls against it. If the panic snap is old and partially rusty, it may not release easily in an emergency, however. For this reason, a horse should also be transported in a leather halter, or a nylon halter with a leather crown piece -- the leather will break if the horse cannot be released from the tie quickly enough.
Alternatively, there are nylon ties with a velcro joint in the middle that are designed to break away easily if a horse pulls against them. The downside is that some clever horses learn to break away from them even when they're not panicked. Some horse owners also attach trailer ties using a small piece of breakable bailing twine -- all methods are acceptable as long as some part of the restraint will break under heavy tension.
Unsafe Trailer Ties
Bungee-style trailer ties are not considered to be a safe alternative for restraining a horse. They usually come attached to panic snaps, but unfortunately the elastic recoil in the bungee cord causes the heavy panic snap to come back at the horse's head rapidly when it's released -- this can result in severe injury to the horse's eye or to human bystanders. It's also possible for the horse to pull hard and fast enough to break the bungee cord, which will also snap back at the horse's head.
Tying a horse inside a trailer with a rope halter, while a very common practice, also has associated safety hazards. Rope halters will not break if the horse struggles against them. A safety release knot must be utilized when tying a horse with a rope halter -- these knots require skill and practice so they don't loosen during transport, but can still be easily released in an emergency situation. A leather halter with breakable tie is a much safer alternative.
Length of Trailer Tie
The length of the tie should be adjusted so your horse can reach his hay net and lower his head slightly to clear his airway, but should not be so long that he can turn his head around or reach over the divider in the trailer. The tie can be attached either to the ring at the cheek of the halter or the lower ring near his muzzle. Observe your horse in the trailer for a few minutes to be sure the length of the tie is appropriate and that the tie is not hitting his eye when he moves around. If you'll be traveling for more than a couple hours, stop along the way and make sure the length of the tie doesn't need to be adjusted as the hay net gets smaller.
Other Trailer Safety Tips
Horses have many delicate structures on their lower limbs that can be lacerated during loading and unloading on a trailer -- protective wraps and bandages can help reduce the likelihood of these injuries. Horses need to be offered water frequently on long trailer rides, especially in hot weather. If a horse is traveling more than 500 miles, he needs breaks when he's untied and allowed to lower his head -- this helps clear dust and particulates from his airway and can help to prevent shipping fever pneumonia on long trips; overnight breaks from trailering are best for the horse's airway. All horses should be trained to load calmly on a trailer -- veterinary or weather-related emergencies may mean your horse needs to be transported suddenly in an emergency situation.
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