Transporting horses for long distances can be a contributing factor in the development of respiratory disease, which can last long after the trip is over. Risk Factors Horses consume less hay and water while traveling, and when transported for extended periods of time, they can become dehydrated.
Dehydration can impair pulmonary defense mechanisms that normally clear infectious material.
Additionally, horses confined with their heads elevated have decreased clearance of infectious material simply due to gravity. Surfactant levels, an important substance in the lungs that helps prevent infection in the alveoli, also are decreased in horses transported for extended periods. Trans-tracheal washes performed on horses after transport revealed an increase in bacterial numbers in the lower respiratory tract. Consequently, horses are exposed to higher numbers of bacteria in their lower airways at a time when their pulmonary defense mechanisms have been impaired by transport. Other factors that contribute to the development of respiratory disease in horses being transported are environmental factors.