Shipping fever
Even if you only haul your horse on shorter trips, it’s wise to be aware of the factors that can cause pleuropneumonia and take steps to minimize the risks.
For many of us, hauling horses is a happy ritual of summer. Wherever we're heading—shows or clinics, parks or parades—road trips usually mean there's a fun
day ahead, full of activities with our horses. Most of the time, our horses seem to share in our enthusiasm, coming down the trailer ramp bright-eyed and ready to go.
Yet for them, as for people, travel has a potential downside: exposure to respiratory bugs and other pathogens, particularly when their destinations are crowded with other horses. “It can be similar to a person catching a cold from the person sitting next to you on a plane,” says Virginia Buechner-Maxwell, DVM, DACVIM, of the Virginia–Maryland College of Veterinary Medicine in Blacksburg, Virginia. And those post-trip sniffles are usually a minor problem. “If horses get a respiratory infection after transport, like people with colds, they usually just get over it. Rest from work may be all that’s needed.”
Sometimes, however, a fever and cough that start soon after a trip are early signs of a much more serious illness: pleuropneumonia (commonly called shipping fever), an inflammation of the lungs and the pleural membranes lining the chest wall, which can cause fluid to build up in the space between the lungs and the rib cage. “This is no longer simply an upper respiratory infection that clears up in a few days,” Buechner-Maxwell says. “If the infection has progressed to pleuropneumonia the resulting fluid buildup between the chest wall and lungs compresses and damages the lung tissue and can have long term effects or even lead to death if not diagnosed and treated quickly.”
If the infection is advanced by the time it is detected, the treatment regimen can be protracted, expensive and at times unsuccessful. Potential complications include laminitis as well as scarring of the lung tissues that may limit a horse’s ability to perform. Chances for a speedy recovery are best when aggressive treatment is begun within the first 48 hours---long before more serious outward signs of illness are likely to be evident.
So even if you only haul your horse on shorter trips, it’s wise to be aware of the factors that can cause shipping fever while taking steps to minimize the risks. And call the veterinarian right away if your horse shows any signs of respiratory illness after transport.
Shipping fever is more likely to occur in horses after they have been in transit for 20 hours or more. That doesn’t mean, however, that horses taking shorter trips have no chance of developing the problem.
A UNIQUE COMBINATION OF STRESSORS
Many situations, including surgery under general anesthesia or repeated, prolonged exertion, can put a horse at risk for pleuropneumonia, but the condition is called “shipping fever” for a reason: Transport presents a unique mix of physical and psychological stressors that can weaken a horse’s defenses.
“Shipping is stressful for horses,” says Amy Johnson, DVM, DACVIM, of the University of Pennsylvania School of Veterinary Medicine, noting that, in addition to the transport itself, a horse must cope with being separated from his home herd and adapting to an unfamiliar environment. “The stress response with various hormones and other substances that are released in the body are immunosuppressive. The immune system then cannot fight off the pathogens that accumulate in the lower airway as effectively.”
Then there’s the physical side of riding in a trailer or van. A horse’s environment during transport may not be any more dusty than his home barn, but if he can’t readily lower his head, airborne particles may take a greater toll on his health. “Putting their heads down is essential to enable the normal mucociliary clearance mechanisms in the airways to do their job in clearing out pathogens and debris from the lower airways,” says Katherine Wilson, DVM, DACVIM, of the Virginia– Maryland College of Veterinary Medicine. “There have been studies showing that even without the trailering aspect, if horses are tied with their heads up for six to 12 hours, they develop accumulations of bacteria and inflammatory cells in the lower airways.”
The duration of a trip also matters. Shipping fever is more likely to occur in horses after they have been in transit for 20 hours or more. In one 2016 study of 869 horses who traveled by air to Hong Kong, 10.8 percent developed shipping fever, and the incidence was higher among horses arriving from Great Britain and the United States than in those from New Zealand and Australia.
That doesn’t mean, however, that
horses who travel shorter distances have no chance of developing shipping fever. “Many factors can be involved,” says Wilson. “Some studies have looked at travel distances and time, but we’ve also seen respiratory disease in horses that have traveled for only a couple of hours. There are also many horses that travel for more than 24 hours and are fine.”
SPOTTING THE EARLY SIGNS
The first indicators of any respiratory illness tend to be subtle so it’s wise to keep a close eye on your horse after a trip. Fever is often the earliest sign of trouble so check his temperature daily--twice a day, if possible---for several days afterward.
“Usually within 24 to 72 hours after shipping, a horse who is coming down with a respiratory infection will develop a fever,” says Wilson. “Sometimes the first thing the owner notices is that the horse is dull and lethargic and doesn’t want to eat. These first signs may progress to nasal discharge and/or coughing but sometimes not.”
Other early signs may include an increased respiratory rate (the normal rate ranges from eight to 12 breaths per minute), or discharge around the eyes. If the pleural membranes are affected, the resulting pain may cause a horse to breathe shallowly and rapidly, take unusually short strides and flinch when touched.
Call your veterinarian when you first notice the signs of illness. “If it’s a viral infection, most horses will recover in a few days, but what you don’t want to do is miss the horse that has something more going on,” says Buechner-Maxwell. “If a horse is coughing and has a nasal discharge and a fever, consult with your veterinarian. This is especially important if the nasal discharge contains pus or smells bad or there’s a change in the horse’s breathing pattern. It is much better to have your veterinarian come out for a minor illness than to wait and find out two days later that the horse is really sick.”
MAKING A DIAGNOSIS
One of the first things a veterinarian will do when examining a horse with post-travel respiratory signs is to determine whether the problem is a less serious upper respiratory infection or a more worrisome inflammation of the lungs (pneumonia). “Opportunistic bacteria set up a bacterial pneumonia, but it can be treated at an early stage and the horse has a very good prognosis for recovery and return to use,” says Wilson. “Otherwise it may progress into a number of more serious conditions, including pleuropneumonia.”
Simply listening to the horse breathe may provide some clues. “Often you can hear some abnormal lung sounds with a stethoscope,” says Johnson. “[Your veterinarian] might not be able to hear any lung sounds at the bottom of the chest but hear them at the top of the chest and become suspicious that there might be fluid in the pleural cavity.”
Your veterinarian may also recommend ultrasound imaging, “which will usually show any disease within the pleural cavity and if there is fluid accumulation,” says Johnson. “It also gives a really good idea about what’s happening at the surface of the lungs and how far into the lungs the disease extends.”
Often, in hospital settings, x-rays will also be taken to look for any issues missed by ultrasound. “If there is an abscess or infection in the middle of the horse’s lung but still some normal lung on the periphery, you could miss that lesion with an ultrasound,” Johnson says. “The ultrasound beam doesn’t penetrate through normal lung containing air. Thus we often take radiographs of the horse’s
Fever is often the earliest sign of trouble, so check a horse’s temperature daily--twice a day, if possible ---for several days after transport.
chest to make sure there is not any deeper disease that is going undetected by the ultrasound.”
Blood tests may also be helpful. “The veterinarian may want to do bloodwork to look at the white blood cell count to see if there is evidence of infection,” says Wilson. “There are also other factors we look at that may be indicative of inflammation. One is fibrinogen, which is included in the complete blood cell count. The other test that has gained in use in the last few years is to measure concentrations of serum amyloid A [SAA]. This is an acute phase protein, which means it increases rapidly when there is acute inflammation in the body.”
Finally, if a bacterial infection is suspected, the veterinarian may have some lab work done to identify the specific culprits. “We might do a tracheal wash to get a sample of fluid from inside the trachea,” says Wilson. “This sample can be cultured, so we’ll know which bacteria are involved. Most of the time, it’s a mix. Anaerobic bacteria [which don’t need oxygen] may form abscesses and cause some of the lung tissue to die. This can be a more serious type of infection.”
HEADING OFF THE WORST
Faced with a horse in the early stages of respiratory disease, one of the first treatment decisions a veterinarian will make is whether an antibiotic is needed. “Viral infections won’t respond to an antibiotic. The horse may simply need medication to control fever. If it’s not a high fever, the horse may not need any medication at all,” says BuechnerMaxwell. “However, viruses often damage the lining of the airway. In some cases when a horse gets really sick from a virus, we may give antibiotics, more as a preventative measure, to combat possible secondary bacterial infections.”
Of course, antibiotics are also warranted when a horse’s signs point toward a bacterial infection at the outset. “If your horse is coughing and there is an odor to the breath, with nasal discharge containing mucus or pus, he is having trouble breathing or is intolerant of normal exercise, he needs treatment,” Buechner-Maxwell says.
Often, a broad-spectrum antibiotic will be prescribed even before the causal bacterium has been identified. “Many people, especially with a sick horse, don’t want to wait to get the results of the culture before starting treatment, so we generally start these horses on a broad-spectrum antibiotic protocol,” Johnson says. Then, when the results of the culture are in, the drugs can always be changed.
“Once these horses are stable enough to go home for continued care, we’d know which oral antibiotics are appropriate for continued treatment,” says Johnson. “There are some people, however, who would only do the tracheal wash and the culture if the horse was not responding to the initial series of antibiotic. I think most people do the tracheal wash initially, but there is not complete consensus on that.”
Other supportive care may include the use of antiinflammatory drugs as well as other analgesics. “The horse may need fluid support if he’s feeling poorly enough that he’s not drinking,” says Wilson. “Bronchodilators can sometimes help, as well. Clenbuterol
During an examination, a veterinarian may use a stethoscope to listen for abnormal lung sounds as a horse breathes.
is a bronchodilator that can improve clearance of the airways.”
The goal in the earlier stages of treatment is to curb the infection before it extends into the pleural cavity. “The earlier you start the antibiotics, the more likely you will have a faster and successful resolution of disease,” says Johnson. “The longer the horse goes without appropriate antibiotic treatment, the more likely he will develop more severe disease or complications with more damage.”
LIMIT YOUR HORSE’S RISKS
Given the practical, emotional and financial toll that shipping fever can take, “the best scenario is to try to prevent infections from developing, and monitor the horses closely after shipping---for a few days to a week,” Wilson says. Here are some measures that can help you protect your horse:
Avoid tying your horse’s head high for prolonged periods. “The biggest factor is that most horses while traveling are tied with their heads up,” says Wilson. “It is important for horses to be able to put their heads down, to clear debris and bacteria out of the upper respiratory tract. If possible, leave horses in a box stall or trailer compartment instead of tied, so they can move around and put their heads down.”
If you must tie a horse in the trailer, to prevent bickering with a neighbor, for example, give him as much slack as possible to let him drop his head below the level of his withers. On longer trips, schedule rest stops at least every four hours, if you can, and unhook the horse’s halter so he can stretch his neck and lower his head.
Also, allow a horse time to recover with his head down after a trip---for example, don’t tie him to a highline for the night after spending all day in a trailer. “[One study] showed that the number of bacteria in tracheal secretions was significantly increased in horses after six hours with their heads elevated,” says Buechner-Maxwell. “In horses who had their heads tied up for 24 hours, it required eight to 12 hours before the airways returned to normal.”
Make your trailer “lung friendly.” Travel with vents and windows open; use screens if you’re worried about debris blowing into the trailer, and blanket the horses if it’s too cold.
Good ventilation is always better for a horse’s lungs, but you’ll also want that air to be clean. “If you are transporting horses with windows wide open and have hay right in their face in a hay net, you might want to do something a little different so the horse isn’t getting a lot of dust in his face,” says Buechner-Maxwell.
Wetting down hay before placing it in the trailer might remove some dust and/or make it less likely to blow in your horse’s nostrils. Also, use a low-dust bedding, if any is needed at all. Dried manure can also be a source of airborne bacteria inside a trailer.
Hose out the trailer thoroughly after each trip, and remove fresh manure at rest stops along the way. “Feeding pellets instead of hay and frequent removal of manure and urine from the trailer have been shown to reduce the insult to the horse’s lungs,” says Buechner-Maxwell.
Avoid unnecessary travel with an ill horse, or one who has only recently recovered from illness. A horse who is sick or who has been ill within the previous week or two may still have a weakened immune response. And if he’s recovering from a viral respiratory infection, his airways may not have fully healed. “Those viruses damage the cilia that line the upper respiratory tract,” says Wilson.
The cilia, the fingerlike projections that line the airways and help capture and remove inhaled particles, can
Avoid tying your horse’s head high for prolonged periods. If you must tie a horse in the trailer---to prevent bickering with a neighbor, for example--give him as much slack as possible to let him drop his head below the level of his withers.
be damaged by a viral infection such as equine influenza, and it takes two to three weeks for them to fully heal, even after the horse has otherwise recovered. Until then, a horse’s ability to expel inhaled pathogens and dusts will be compromised.
Vaccinate as appropriate. If you frequently take your horse to shows or other venues where he will encounter many other horses, consider having him
vaccinated against rhinopneumonitis, influenza and possibly strangles. Limiting his risks of exposure to illnesses like these may prevent more serious infections from gaining a foothold.
“If you plan to show the horse through the summer, talk with your veterinarian about the best vaccination protocol for the area where you live,” says BuechnerMaxwell. “If you are going to show all summer it may be best to vaccinate ahead
of the show season and then give a booster if you are on the show circuit for more than four or five months.”
By taking steps to limit your horse’s risks of developing shipping fever, and acting quickly when you notice the earliest signs of illness, you and your horse will likely be able to keep on rolling for many years to come.