Transportation and Respiratory Disease in Horses

Transportation commonly takes a toll on horses, particularly on their respi­ratory health. Horses can develop what is known as transport-asso­ciated respiratory disease. Many factors, including pre-existing airway inflam­mation,^1,2 head position,^3-5 and journey duration,^6-8 increase the risk of horses’ developing this disease.

Why some horses develop transport-associated respi­ratory disease and others do not remains unknown, underscoring the need for a multidisciplinary approach to evaluating equine transport and the many factors that contribute to the associated respiratory disease.

To address this need, a multinational research team conducted a first-of-its-kind study to evaluate the effects of transportation on behavioral, clinical, environmental, and respiratory parameters and then determine whether these parameters were associated with one another. The findings are the first, the inves­tigators wrote, “to relate behavioral changes during transportation to subsequent lower airway bacterial proliferation, contamination, and inflammation.”⁹

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Experimental Design

Twelve healthy adult horses aged 3 to 8 years with prior transportation experience were evaluated. They were acclimated for 2 weeks before transportation. On transportation day, the horses were grouped into 2 sets of 6 and went on an 8-hour trip; the trips were identical and occurred 48 hours apart. During the trip, horses were housed in individual stalls and were not offered food or water. There was one 25-minute rest stop for the driver.

Before, during, and after transportation, clinical, environmental, behavioral, and respiratory param­eters were assessed. Statistical analyses were performed to determine associations between clinical and behavioral parameters.

Clinical Parameters

Horses were evaluated clinically at preloading, unloading, and specific time points after the journey (AJ). All horses were clinically normal at preloading.

Transportation significantly affected several clin­ical parameters. At unloading, 10 of the 12 horses had decreased borborygmi in at least 1 quadrant. In addition, heart rate, respiratory rate, and rectal temperature were significantly higher at unloading than at preloading, then decreased to near-preloading levels by 12 hours AJ. Body weight was significantly decreased at unloading, then increased to near-pre­loading levels by 5 days AJ.

At unloading, 6 horses had audible coarse airway sounds, coughing, or both that remained for 5 days AJ. For the analysis, these horses were catego­rized as group AB; the other 6 horses with normal lung sounds on auscultation were categorized as group N.

Environmental Parameters

The investigators installed a weather tracker and a gas detector in the stable boxes before transport and in the last stall in the truck on transportation day, both at horse head height. The weather tracker collected data on temperature, humidity, and air movement; the gas detector measured concentrations of oxygen and noxious gases. Temperature and humidity were highest in the afternoon, and air movement increased when the truck was moving. Noxious gases were not detected.

Air samples were collected in the stable boxes and in the truck at preloading and unloading to measure bacterial concentrations. For each environment, bacte­rial concentrations were generally similar before and after transportation.

Behavioral Parameters

Horse behavior was video recorded in the stable boxes on the day before travel and in the truck on transpor­tation day. Numerous behaviors, particularly those related to stress (eg, licking/chewing, pawing) and balance (eg, leaning on stall rails) were analyzed by an experienced ethologist.

Compared with the rest stop and stable box, trav­eling elicited the highest frequency of balance- and stress-related behaviors. Regarding trip duration, stress-related behaviors were most frequent during hour 1, then generally decreased. Balance-related behaviors decreased until hour 5, then peaked during hour 8. Taken together, these findings suggest that horses need several hours to adapt to transportation and may become fatigued with long travel durations.

During the trip, nervous and agitated horses nega­tively affected their neighbors, highlighting the importance of considering temperament and travel experience when grouping horses for transportation.

Horses kept their heads down for longer time periods with each successive hour of travel. Interestingly, stressed horses kept their heads up longer during traveling and at the rest stop, increasing the like­lihood of airway mucus and bacteria accumulation.

Bloodwork

The investigators collected venous blood samples at preloading, unloading, and several AJ time points. Cortisol levels were significantly higher at unloading than at preloading and then steadily decreased, suggesting the transportation is an acute stressor for horses. Lactate and creatinine kinase also significantly increased during transportation, indicating increased muscle movement. Other notable changes at unloading included increased neutrophil counts and decreased potassium.

Arterial blood samples were collected for blood gas analysis. Transportation had no measurable effects on blood gas or pH values.

Respiratory Parameters

Using respiratory endoscopy, the investigators subjectively graded tracheal inflammation (none to extreme), tracheal mucus (none to profuse), and tracheal wash turbidity (transparent to opaque) and color (clear to blood). Tracheal inflammation and mucus scores were generally higher for group AB than for group N; tracheal mucus scores were lowest at preloading. Tracheal wash turbidity and color increased progressively during trans­portation and did not return to normal by 5 days AJ.

Tracheal wash samples also underwent cytologic and bacteriologic anal­ysis. Cytology results revealed the highest percentage of neutrophils at 24 hours AJ; notably, group AB horses had persistent airway neutrophilia, even 5 days AJ. Bacteriology results revealed significant increases in bacterial concentration in all horses at unloading, with the highest concentrations in group AB. Pasteurellaceae-like bacteria were the predominant bacteria; this differed from the bacteria in the air samples, which contained predom­inantly Corynebacteriaceae, Yaniellaceae, and Staphylococcaceae.

Analyzing the microbiome in the tracheal wash samples, the investiga­tors observed marked decreases in bacterial diversity from preloading to unloading, indicating the negative effect of transportation on respiratory flora diversity.

Associations Between Parameters

The investigators identified several associations between the behavioral and clinical parameters:

• spent with the head down negatively correlated with tracheal mucus and inflammation scores and tracheal wash bacterial concentration.
• movement en route positively correlated with total protein and creatinine kinase levels at unloading.
• rate at unloading positively correlated with balance-related behaviors.

Study Omplications

For the first time, “this multidisciplinary study…related [clinical] changes to observed behavioral responses to transportation,” the investigators wrote. Given the study’s findings, the authors proposed a number of recommen­dations for equine transportation:

• Consider the social transmission of anxiety and arousal in horses when grouping them for transportation.
• Perform a thorough clinical examination before and after transportation to assess subclinical airway inflammation.
• Monitor horse behavior en route.
• Allow horses to rest for at least 24 hours following transport to allow lactate and creatinine kinase levels to return to normal.

Such recommendations could not only help identify horses that are at increased risk of transport-associated respiratory disease, but they may also decrease the incidence of the disease.

Dr. Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.

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