Canadian sport horses tend to make two big migrations each year – the long drive to the winter circuits in Florida or California, and the long drive home. If your horse is one of these long-distance travelers, there are health hazards that you should be aware of during and after the trip.

One of the more serious complications is pleuropneumonia, commonly known as shipping fever, which is fluid in the lungs and pleural cavity that can become so severe it requires intense treatment in hospital. But why does a long trailer journey put your horse at greater risk for developing pleuropneumonia?

Long trailer rides have been shown to weaken a horse’s immune defenses, mainly due to an increase in stress hormones, such as cortisol, that it triggers. When cortisol is high for a long period of time, the body’s white blood cell levels decrease. White blood cells are responsible for fighting any infection that the body may encounter, and when there are less of them circulating throughout the bloodstream, the body is less able to handle any insult the environment may throw at it.

The trachea (windpipe) contains cilia, microscopic finger-like projections that beat back and forth in synchrony and are responsible for moving dirt and debris up and out in the opposite direction of the lungs. The horse can then cough out any bacteria, debris and mucous that may be moved out of the upper respiratory tract. When horses are on the trailer, their heads are often tied up to ensure they don’t turn around in the trailer stall or otherwise get into any mischief. However, this inhibits their ability to lower their head to clear their trachea. There have been many studies that have shown that horses with their heads held in an upright position for an extended period of time have taken longer to clear dirt and debris out of the trachea, therefore leading to more insult on the lower respiratory tract.

Finally, the longer the horse stands on the trailer, the more likely it is to urinate. Having urine on the trailer floor increases the ammonia in the air; this, along with dust from the road, is not a healthy respiratory environment for the horse to be in for a long period of time. Similar to horses that have respiratory problems in the barn, it is essential to have proper ventilation in the trailer as well.

If caught quickly, shipping fever can resolve without many complications, but it’s important to know what to look out for. Clinical signs generally appear 24-72 hours after trailering. Symptoms such as fever, depression, coughing, nasal discharge and lack of appetite are reliable indications that something may be wrong. It is a good idea to let your veterinarian know immediately when you notice something awry with your horse; this is especially true after shipping long distances.

Shipping fever is diagnosed using a variety of modalities including blood work, ultrasound, and occasionally using a trans-tracheal wash. Your veterinarian will start off by getting a thorough history from you or the horse’s caretaker. This will include questions including: when did the symptoms start, what are the symptoms, has the horse shipped recently, etc. Then your vet will proceed with a physical exam, likely focusing on the lungs, trachea, and mucous membranes. Listening to the lungs can give your veterinarian an idea of the severity of the problem. Normal lungs should be barely audible when you listen to them with a stethoscope; audible crackles, wheezes, and rattles indicate pathology in the lungs.

Depending on the clinical signs, your vet may choose to pull blood and ultrasound the lungs. Blood work enables veterinarians to determine red blood cell counts, white blood cell counts, and internal organ function. Results can dictate whether antibiotics and IV fluid therapy should be initiated.

Performing an ultrasound of the lungs allows the lung field to be visible. Your veterinarian will look for changes on the surface of the lungs which can range from roughening on the lung surface to lung consolidation (areas filled with fluid instead of air) to actual abscesses in the plural space.

If the shipping fever has progressed to full-blown pneumonia, your veterinarian may choose to perform a trans-tracheal wash. This diagnostic procedure allows for a sterile sample collection of fluid and cells within the lungs which enables your veterinarian to better target an antibiotic to treat your horse.

Preventing shipping fever isn’t always something that can be accomplished, but there are certain steps you can take to reduce the risk of your horse getting sick:

  • Vaccinating your horse for major respiratory viruses such as influenza and equine herpes virus will provide the body with the tools it needs to prevent infection.
  • Ventilation in the trailer is key. Make sure windows and vents are fully open to allow airflow, especially once horses have urinated. Improving air quality can also be done by soaking hay and feeding in a slow-feed haynet to reduce dust.
  • When you stop for gas, allow the horse to lower his head. If you can find a safe place to unload (not the side of the road!), you can allow the horse to rest and graze. Lowering the head allows the horse to clear dirt and debris out of his trachea, therefore reducing the bacterial load on the body.
  • Do not ship sick horses. Even if your horse was exhibiting clinical signs of illness 1-2 weeks prior, its immune system may not have recovered to normal function yet. Running blood work prior to travel can identify any indication of inflammation or infection.
  • Finally, know what is a normal temperature, pulse, and respiration rate for your horse. You can monitor these on the journey (as long as it’s safe to do so) and after arriving at your destination. A noticeable rise in temperature or respiration rate can allow for quick veterinary intervention and hopefully a better prognosis for your horse.

There are some who believe that giving antibiotics to a horse prior to shipping will help prevent any infection. There have been multiple studies done which show that this preventive measure is ineffective and in fact can lead to antibiotic resistance.

If you are planning a long journey with your horse, reach out to your veterinarian in order to make a plan. He or she may suggest blood work, running IV fluids prior to leaving, and can make recommendations regarding how often to stop and give your horse a break. Happy travels!