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