Long-distance transport compromises horses’ natural immune defenses. | Photo: Erica Larson/The Horse

As the winter approaches, many horse owners are preparing to migrate south to warm weather spots like Aiken, S.C., or Ocala, Fla. These regions can offer comfortable temperatures and well-ventilated barns even in the dead of winter—a great advantage to your horse’s respiratory health. However, traveling to these locales can put your horse’s lungs and airways at risk. 

Shipping fever is a well-described pulmonary disorder appearing in animals shipped long distances. If left untreated, cases of this pneumonia type can become severe enough to require hospitalization and even endanger a horse’s life. 

So, why do horses get shipping fever in the first place? Long-distance transport compromises horses’ natural immune defenses. It has been shown to increase levels of stress hormones, such as cortisol, which can impair immune function. It can also affect tracheal clearance. Microscopic fingerlike projections called cilia cover the trachea lining. These beat synchronously to move dust, debris, and bacterial particles up the trachea and away from the lungs, where horses can cough it up. Trailered horses are commonly cross-tied so each animal’s head is fixed in an upward position. Studies have shown that this prolonged upward fixation of the head and neck significantly decreases the rate at which inhaled foreign particles move out of the trachea. This leads to a significant increase in the number of inflammatory cells and bacteria in the trachea and lungs. Combine this with a weakened immune system, and it’s no surprise some horses develop pneumonia after shipping