By: Joan Norton VMD, DACVIM

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 defences. It has been shown to increase levels of stress hormones, such as cortisol, which can impair immune function. A study completed in Poland in 2015 showed a significant increase in systemic inflammation when horses are shipped 50km and 550km. Shipping can also affect tracheal clearance. Microscopic finger like 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.

There are steps, however, that you can take to prevent your horse from developing shipping fever: First, do not ship sick animals. Horses with already-compromised immune systems or those recovering from a recent illness are more likely to become sick after shipping. Upper respiratory tract viruses can blunt tracheal cilia, making them less effective at clearing bacteria and debris. This damage can take weeks to a month to heal, leaving a horse even more susceptible to infection when shipped.

Once your horse is on the trailer, try to decrease the amount of dust, debris and bacteria he must inhale. Ensure the trailer has good ventilation, especially in the winter when our common (and incorrect!) instinct as humans is to close all of the windows. To prevent airborne debris, soak hay for five to 10 minutes before hanging it in hay nets, or ship without offering hay. Also, let gravity lend a hand. One study showed that handlers can negate the ill effects of an upward fixed head position by allowing the horse to lower his head to the ground several times throughout the trip. So when you stop for gas, let your horses have their heads; they might be able to clear some of the particles they’ve inhaled.

Researchers have performed studies evaluating preventive medical treatments, but none have been shown to be very effective. Pre-shipping antibiotic administration does not prevent all cases of pneumonia and the risks of using antibiotics unnecessarily – fuelling antibiotic resistance among bacteria – outweigh the potential benefits. One study investigated the use of clenbuterol (Ventipulmin) as an approach for preventing shipping fever. Clenbuterol has been shown to increase the speed at which horses clear foreign particles from the trachea. However, expediting clearance was enough to prevent some of the study horses from developing characteristic fever, cough and nasal discharge.

Unfortunately, shipping fever will still occur no matter how diligent we are. The best thing is to recognize and treat the illness early. After travel, monitor horses’ attitudes and appetites and note any coughing or nasal discharge. Take each horse’s temperature daily to help identify fever, which can be an early sign of illness. If you do have concerns about one of your travellers, contact your veterinarian. He or she can assess your horse and might recommend blood work to look for signs of systemic inflammation or ultrasonography to evaluate the lungs. Treatment consists of antibiotics, anti-inflammatories and supportive care. Many times pneumonia in horses, if treated early, can be resolved without too much time off from riding.

About the Author: Joan Norton VMD, DACVIM founded Norton Veterinary Consulting and Education Resources to promote equine veterinary education to horse owners, professionals and veterinarians. She is the author of Equine First Aid Handbook. This article is provided courtesy of AAEP Media Partner, The Horse.

Reviewed and updated by original author in 2016.