Md. Code, Agriculture § 3–902

(a) A person may not transport a horse in a vehicle that is not designed and constructed in a manner that at all times protects the health and well-being of the horse being transported.

(b) To meet the requirements of subsection (a) of this section, at a minimum, a vehicle used to transport a horse shall:

(1) Be limited to one level throughout the vehicle where animals are confined;

(2) Have an interior height sufficient to allow each horse being transported to stand with its head extended to the fullest normal upright position without making contact with the roof or an overhead structure;

(3) Have doorway heights and widths that allow a horse to pass through without touching the sides of the openings;

(4) Be equipped with ramps if the vertical distance from the floor to the compartment containing the horse is greater than 15 inches;

(5) If the vehicle is equipped with ramps that sit at greater than a 25 degree angle, have ramps equipped with antiskid flooring and rails; and

(6) Contain adequate space to ensure that no horse is crowded in a way that is likely to cause injury.