Complications of this transit-associated respiratory disease can be minimized with careful planning

by Barbara Sheridan

FOR MOST RACEHORSES, transport is a common occurrence in their lives, but many owners are unaware how shipping can profoundly affect their horses' health. Horses that travel long distances are particularly susceptible to developing pleuropneumonia, commonly referred to as travel sickness or shipping fever.

A respiratory infection that affects the lungs and pleural (chest) cavity in horses, shipping fever quickly can become a serious and potentially debilitating or even fatal disease if not recognized and treated early.

"Pleuropneumonia is a bacterial pneumonia that becomes severe enough so as to affect both lungs and extend into the pleural space surrounding the lungs," said Corinne R. Sweeney, D.V.M., a veterinary internal medicine specialist and professor at the University of Pennsylvania's New Bolton Center in Kennett Square. "While a horse can get [pleuropneumonia] by not even leaving its stall--for instance, if it's suffering from an acute viral disease--it is often associated with transporting horses over an extended distance."

Sweeney added that this disease is commonly seen in Thoroughbred and Standardbred racehorses, which often are shipped long distances.

"When shipping horses, an elevation of environmental temperature and relative humidity occurs along with an increase in the number of bacterial organisms in the air," Sweeney said. "The changes in their environment, combined with the stress from transporting, can affect their respiratory system and may predispose them to this disease."

Minimizing complications

For centuries, equine transportation has been synonymous with horse ownership. While the mode of travel may have advanced with time, from rail to wheels to wings, the effects of pleuropneumonia remain unchanged.

"This condition has indeed been around for a long time and was a significant cause of mortality for infantry horses during the Boer and First World Wars, when horses were literally 'shipped' into battle," said Sharanne Raidal, B.V.Sc., Ph.D., senior lecturer in veterinary physiology at Charles Sturt University in New South Wales, Australia.

Antibiotics were not available back then, so several measures were introduced to help offset this disease, including the application of avoidance tactics, such as pre-travel monitoring, correct transport methods, and surveillance. These recommendations hold true today.

In a research study, Raidal and her team from the Department of Veterinary Pathology at the University of Sydney in New South Wales evaluated the direct effects of transportation on the internal environment of the lungs. They concluded that a certain amount of airway compromise successfully could be avoided through simple prevention.

"It's important to make sure that the horse is well in every other respect before traveling," said Raidal. "A low-grade viral respiratory infection may make it easier for the bacteria to move from the airways to the lungs and slow mucociliary [mucous membranes of the respiratory system] transport. Some sedatives also will slow mucociliary transport and should be avoided."

Raidal noted that shipping disease appears to be caused by factors associated with transport.

"The stress relating to travel, head position, changes in ventilation, and air quality that occur when one is being transported by horse trailer or van, and the length of transport are all contributing factors," she said. "Normally, it's not associated with short-term travel, say one to four hours. But, rather, it affects horses transporting at a greater distance."

Sweeney pointed out that causes could be many individual factors that come together.

"Often horses are going from one site where they've been gathered together, such as a racetrack or a holding area, to a new site where they're introduced to new horses," she said. "Tired and stressed, the natural immune cells in their lungs are not as effective. We see the same thing in horses as we do in people."

Lower respiratory problems

In a study published in the Equine Veterinary Journal, researcher Carolyn Stull, Ph.D., an extension specialist at the Center for Equine Health at the University of California at Davis, investigated the effects of long-term transport on horses. She concluded that the susceptibility to infectious illness in horses increased when the immune system of travel-stressed horses became compromised.

"Start with a healthy horse and, if you're going to haul with other horses, make sure they're healthy, too," Stull said. "If the horse is sick or its immune system is compromised, it's only going to further progress. This seems to be something that people don't understand or don't evaluate effectively."

Sweeney agreed, adding: "Transporting a horse that is suffering from a low-grade viral infection or one that is tired and dehydrated after racing can also increase the risk. Also look at the transport and determine how you might minimize the stress. If you're going across country, try to stop and stable them along the way. If that's not possible, then allow them to get off periodically and make sure they're both eating and drinking. And, ideally, you shouldn't be picking up any new horses along the way to which they hadn't been exposed."

According to Stull, head position of the horse and restricted movement during travel also can compromise the respiratory system. "We found that horses loose in similar square footage had much less of an impact on their immune systems  than horses that were cross-tied," she said.

Short-tying a horse so that it was unable to lower its head compromised the health of the lower airways, making it more difficult to drain, and increased the number of bacteria found in its airway passage. The method of long-tying--attaching through the cheek ring of the halter in a safe manner--or leaving the horse loose in a box stall during shipping allows the horse to snort out mucus and clear the airway.

"If the horse has its head in a more natural position, which is below its withers, this allows for sinus clearing and airway drainage," Stull said. "Proper ventilation and minimizing dust levels also help to maintain proper respiratory function."

While they had only studied horses that were traveling long distance, Stull's team monitored and took samples as they went through the entire shipping process.

"Our results indicated that the initial hour, which involved loading, adjusting, and getting going, was certainly a point that initiated the stress response," said Stull. "Face it, when he's being loaded, that horse doesn't know whether he's going for an hour or 24 hours. So that can be a stressful point for the horse."

To help keep the stress levels down, horses typically are offered rich, quality hay via a hay net or an elevated feed manger. However, as the horse nibbles away at the hay, dust and small hay particles are released into the air directly at nostril level, which allows floating debris to overwork the mucociliary system in the respiratory tract. Stull instead recommended offering a grass hay that is free from dust and small particles and feeding it on the floor of the trailer or van to encourage natural lowering of the head and draining of the airways. Soaking or dampening the hay also can help cut down on dust particles.

Raidal added that administering antibiotics to healthy horses before travel as a common form of prevention proved ineffective. "We found that treating them with antibiotics prior to and/or during transportation was associated with the isolation of increased numbers of enteric bacteria, which is bacteria normally found in the intestines. The antibiotics actually killed the 'easy to beat' bacteria, making it easier for the other bacteria to multiply. The bottom line was that because we weren't preventing the buildup of airway secretions and bacteria, we were not preventing the problem."

Early recognition crucial

Symptoms of pleuropneumonia may not be visible for two to three days following transportation. If left unobserved or untreated, this disease can progress rapidly to death within 30 days after shipping. Clinical signs include fever, depression, nasal discharge, cough, loss of appetite or thirst, a colic-like appearance, and an increased or abnormal respiratory pattern--all of which can appear during travel or within 24 hours after transport.

Many veterinarians recommend keeping the horse properly vaccinated against respiratory diseases as well as monitoring the horse's temperature prior to transport, during transport, and soon after arrival to catch the disease early.

"Suspected pleuropneumonia is usually treated with broad-spectrum antibiotics in order to kill a wider array of bacteria," Sweeney said. "Treatment would occur over a number of weeks, and, of course, the horse could be out of training for several weeks to several months so that it doesn't have a relapse, and that's just when it's in the early stages. We may also choose to give some additional treatments, possibly an anti-inflammatory medication to make the horse feel comfortable enough to eat and a bronchodilator to help the horse breathe easier by opening the airways.

"In the early stages, antibiotic medications alone are effective, but as the fluid starts to accumulate into the pleural space and we're more into the second or third stage, we then will decide if the horse would benefit from draining," she said.

Draining involves placing a catheter in the pleural space surrounding the lung and removing the fluid. According to Sweeney, this decision usually is based on ultrasound results.

"As this disease becomes more severe, it becomes almost incumbent to drain some of the fluid because the fluid is causing the horse more distress by pushing on its lungs. Sometimes we can remove up to 30 liters of fluid," she said.

If undetected or unintentionally ignored, which is common in the early stages when the horse is not showing overt symptoms, pleuro-pneumonia has the potential to worsen rapidly.

"Should you think your horse is unwell, seek veterinary advice early," said Raidal, who noted that some people prefer to take a wait-and-see attitude with the hopes the horse will get better. "We have learned so much about how this disease develops, what type of bacteria are involved, and why it is so difficult to treat these horses if the disease becomes advanced. Early, appropriate treatment is the key to successful intervention."

Barbara Sheridan is a freelance writer based in Ancaster, Ontario.