Basics
Made of aluminum, fiberglass or stainless steel, the floors of horse trailers range from just 11 feet long for two-horse transportation to as long as 24 feet for five horses. They invariably have two axles, whether in double- or several-horse configurations, with tires that range from 15 to 16 inches. A standard "gooseneck" or fifth-wheel trailer will be about 7 feet wide and tall. Depending on what they're made of, a trailer can weigh as little as 150 lbs. and as much as several thousand.
Commonalities
Most states require horse trailers to be equipped with brakes if they'll be over a certain limit, such as 3,000 lbs. or more in Wisconsin -- the approximate weight of a trailer with just one horse. Most of these brakes are electronically operated as of 2011, but some hydraulic varieties are still used. Most trailers also include padded walls, floor mats and ventilation windows so horses have an easy time breathing and relaxing during long trips. Multi-horse trailers will have internal compartment doors.
Safely Loading
A single ramp in the rear is a common setup for most horse trailers; however, some trailers are equipped with double ramps: one in the back for horses to enter the trailer, the other near the front, so they can exit the trailer by continuing to walk forward. This method is lauded for being safer and helping horses avoid falls while backing down a ramp. A range of floor mats in different materials like rubber or plastic can help your horses maintain their balance.
Other Features
Depending on how much you pay, your horse trailer could have a range of other amenities to make you or your horses happier and safer. These include: interior dome lights for nighttime travel; safety chains; door locks; built-in food bags; adjustable doors and walls for changing the configuration of the bays; and storage areas, which are more prevalent over the truck bed in fifth-wheel models.