A single injection of a specific antibiotic prior to a long trailer journey can prevent shipping fever with few potential side effects, according to a study from Japan.

Japan Racing Association and Kagoshima University researchers recently investigated the potential of the antibiotic marbofloxacin for preventing the respiratory infection known as “shipping fever,” which can develop when a horse is confined to a trailer and unable to lower his head for extended periods of time. A previous study had shown that a similar antibiotic, enrofloxacin, could prevent shipping fever, but it was irritating, often leading to tissue necrosis at the injection site.

“Both enrofloxacin and marbofloxacin are members of the fluoroquinolone antibiotic class, which is effective against the bacterium responsible for shipping fever and can maintain that antibacterial activity for at least 24 hours,” explains Professor Seiji Hobo, DVM, PhD.

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For the study 48 healthy 2-year-old Thoroughbred racehorses were divided into three groups: One was treated with 2 mg/kg marbofloxacin, one with 5 mg/kg enrofloxacin and one with 10 milliliters of saline. Within one hour of the injections, the horses were loaded into a van and shipped for 26 consecutive hours.

The horses were monitored during and after the trip for signs of shipping fever, including fever, cough or lethargy. Researchers also collected blood samples before and after the trip and analyzed them for levels of the inflammatory marker serum amyloid A, as well as the ratio of neutrophils to lymphocytes, an index of bacterial infection.

The data showed that the horses treated with marbofloxacin had significantly lower post-transportation neutrophil-to-lymphocyte ratios as well as lower levels of serum amyloid A than did untreated control horses. None of the horses in the marbofloxacin-treated group developed a fever after shipping, while one of the horses in the enrofloxacin group and two in the control group did. All the study horses had also been treated with interferon-A to boost immune function, but Hobo says similar results have since been obtained without interferon and are pending publication.

This study, Hobo says, supports the use of marbofloxacin prior to any long-distance shipping—a practice, he emphasizes, within acceptable use for antibiotics. “The possibility that resistant bacteria appears by the single dose of an antimicrobial agent is extremely unlikely,” he says, adding that the preventive measure isn’t needed if the transportation time is less than 20 hours. “In past investigations, shipping fever is typically observed 20 hours or more after the start of transportation.”

Reference: “Effects of pre-shipping marbofloxacin administration on fever and blood properties in healthy Thoroughbreds transported a long distance,” The Journal of Veterinary Medical Science, October 2014

This article first appeared in EQUUS issue #448