Transport and the Immune System

In a study published in the Equine Veterinary Journal investigating the effects of long-term transport on horses, Carolyn Stull, DVM, showed measurable changes in immunological status. She also found the immune systems of transported horses took about 24 hours to recover, making travel-stressed horses more prone to problems upon arrival at their destinations.

According to Stull, an extension specialist at the Center for Equine Health at University of California, Davis, "The horses' immune systems (in the study) were suppressed at every level, significantly increasing their susceptibility to infectious illness."

Blood tests performed on the horses demonstrated that the immunological suppression associated with travel persisted for 24 hours after transport. During this window of "immunological uncertainty," horses need careful management--if they're exposed to pathogens at this time, they are much more susceptible to infection.

Stull transported 12 mature horses, restrained with cross-ties, 1,021 miles in 24 hours. Horses had free access to alfalfa hay and were offered water at regular intervals. The horses were moved in a well-designed, well-ventilated van, but still their immune systems were negatively impacted.

Although cross-tying horses during transport is common, cross-tied horses experience greater stress than horses traveling with unrestricted heads. Cross-tied horses are more likely to suffer from dehydration and immune system dysfunction--during and after travel--than horses moved in box stalls without head restraint.

"Horses normally don't hold their heads above their withers for any length of time," Stull explained. "An elevated head position not only increases the number of bacteria in the respiratory tract, it also suppresses the immune system, making horses more vulnerable to travel-related illnesses."

Stull evaluated the effects of a commercially available nutritional supplement on shipped horses. The product includes extracts of Siberian ginseng, Chinese magnolia vine, Arctic root, and Asian devil's club.

In humans, this formula has shown "adaptogenic" properties that counter the impacts of stress on immune function. Stull said the supplement was well tolerated, but it didn't exert a measurable effect on their immune systems. "The product may be advantageous in lower-stress situations," she said. "It's likely that the stress was severe enough to overcome any immunological benefit this supplement has to offer."

About the Author

Rallie McAllister, MD

Rallie McAllister, MD, grew up on a horse farm in Tennessee, and has raised and trained horses all of her life. She now lives in Lexington, Ky., on a horse farm with her husband and three sons. In addition to her practice of emergency and corporate medicine, she is a syndicated columnist (Your Health by Dr. Rallie McAllister), and the author of four health-realted books, including Riding For Life, published by Eclipse Press and available at or by calling 800/582-5604.

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