How Does Transport Impact Senior Horse Immune Function?

How Does Transport Impact Senior Horse Immune Function?

The senior horses in Dr. Amanda Adams' herd experienced decreased immune function and elevated stress hormones following transport, changes that could take more than a month to return to normal levels.

Photo: Amanda A. Adams, PhD

Researchers have long known that transportation can be stressful for horses—not only for their minds but also for their bodies. Still, scientists haven’t yet zeroed in on all the ways travel impacts horses’ body systems. They have proven that transport negatively impacts the immune function of other species, including cattle and swine, but little is known about the horse, and there’s no work investigating the impact on senior horses.

So recently, Alessandra Campana-Emard, a student at the University of Kentucky (UK) working under the direction of Amanda Adams, PhD, an associate professor at UK’s Gluck Equine Research Center; and colleagues including Suzanne Schindler, a veterinary student at Lincoln Memorial University, in Harrogate, Tennessee, set out to determine how transport impacts horses’ immune systems. Specifically, they studied a group of horses that could be particularly at risk when immune function is diminished: senior horses.

“Senior horses, comprising a significant percentage of the equine population, travel frequently … which is of concern for two reasons,” Campana-Emard said. “First, it has been shown that, with increasing age, there is a decline in immune function and an increased production of inflammatory cytokines,” which results in a chronic, low-grade state of inflammation known as inflamm-aging.

“Second, it is imperative to understand the impact of age and traveling stress on immune function to determine if the transportation of older horses may increase their susceptibility to infection and, if so, for how long,” she said.

Campana-Emard said the team hypothesized that, following short-distance transportation:

  • Stress hormone (cortisol) levels would increase;
  • Cell-mediated immune responses (which protect the body against intracellular organisms, such as viruses, using special white blood cells called T-cells; the T-cells recognize when a cell has been infected by a pathogen and act to eliminate it before the pathogen can replicate) would decrease; and
  • Inflammatory cytokine production would increase.

The team used 16 senior horses with an average age of 25 years. They collected baseline blood samples and evaluated clinical parameters a week before a 1.5-hour trip. They gathered the same samples and data 15 minutes before the trip, 15 minutes after, and on Days 3, 7, 14, and 21 after transport.

Some of the team’s key findings included:

  • Horses had decreased INF-γ (interferon-gamma, an inflammatory mediator produced by lymphocytes) production starting 15 minutes after travel and through Day 21;
  • After transport, lymphocyte gene expression showed reduced INF-γ, TNF-α (tumor necrosis factor alpha, a cytokine involved in mediating systemic inflammation), and IL-10 (interleukin-10, another anti-inflammatory cytokine) levels;
  • Cortisol levels were increased 15 minutes after travel;
  • There were no differences in whole blood gene expression before and after transportation; and
  • Horses’ body weights decreased on Day 3 post-transport.

So what do these results mean?

“Horses transported experienced decreased immune function and elevated stress hormones,” Campana-Emard said, “and these changes may take more than a month to return to normal levels.”

Adams said owners can use these results when deciding when and if to transport their senior horses, as well as after transport.

“Given transportation has an impact on immune function it is important to ensure recovery time for horses after being transported and to watch for any signs of illness, including decreased appetite, temperature, or nasal discharge,” she told The Horse. “It is also important to implement biosecurity measures to reduce exposure or introduction of disease, as the immune response may be weakened and not able to combat as efficiently after travel. Most definitely avoid transporting a horse that is sick or even slightly sick, especially those with respiratory illness.

“Following general and practical guidelines to minimize stress during transportation is important with consideration to duration of travel, offering dust-free hay, providing clean water every three to six hours, and orientation in the trailer,” she added.

Moving forward, Adams said she and colleagues are working to determine “if there is anything we can do in terms of nutrition or supplementation to support the immune system of the horse during transportation.”

Additionally, she said, she and her team plan to conduct studies over the next year to determine whether young and adult horses yield similar results to the senior horses.

“More importantly, we plan to determine if previous history of travel may have an effect on the immune responses or not,” she told The Horse. “For instance, if the horses are acclimated to travel, will we still see dramatic changes in immune function as we saw in this study using horses that only recently travel once per year at the most?”

Adams added, “We recognize that we’re not going to stop transporting horses, but the goal of this research would be to improve how we manage and support horses through travel.”

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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