unloading horse from trailer

By Amanda A. Adams, PhD, and Erica Jacquay, MSc

Q:  After listening to the podcast about horse transport and stress, I wonder: Would it be less stressful for horses if they could see where they were going while being trailered? Cars have windshields … why not horse trailers?

A: Great question. I have a feeling it has more to do with the design of most trailers from the end of the manufacturer. A lot of trailers have forward-facing windows in straight-load trailers and windows that can be put down in slant load trailers that horses can see out of. However, the windows mainly function to improve ventilation and air flow (with grates for safety). There has not been any research in this area specifically, possibly due to the variability in trailer design and layout; however, researchers have looked at the space in the trailer and direction in which horses are facing. Results from a study conducted in 2020 found that horses transported in a wider bay size and that faced the rear had better balance than horses in single bays, but there was no difference in trailer space and body position on cortisol (the “stress” hormone)¹. They also found that increased loss of balance was related to an increased risk of developing gastric ulcers during transportation. While more research needs to be done in this area, it suggests there are still ways we can change current management practices to improve horse health when trailering.

Q:  And what about the stress on a new horse? I just bought a horse and am trailering him up several hours across the state to his new home. What do we know about trailering those distances, and what can I do to minimize his stress?

A:  While our research has focused on shorter distances of around 1.5 hours², there have been other studies that have investigated the impact of stress and horse health in longer journeys. In studies looking at both short (one-hour) and longer (three- to eight-hour) journeys, there is an immediate increase in cortisol (in saliva and plasma) at the start of the trip that remains elevated after unloading in short journeys but declines over time in longer journeys3,4. In longer journeys the stress response might not be as critical as other factors, such as dehydration and having to balance and adjust to the trailer movement over extended periods, which could lead to muscle fatigue4. Heart rate and packed cell volume were also increased in response to loading on the trailer regardless of trip length. This study also found that horses on shorter journeys did not adapt or settle to traveling as well as horses on longer journeys. This could be seen through increased movement throughout the duration of transportation on shorter trips.

This article previously published on TheHorse.com has some great resources on how to reduce stress when trailering.

References:

  1. Padalino, B., & Raidal, S. L. (2020). Effects of Transport Conditions on Behavioural and Physiological Responses of Horses. Animals : an open access journal from MDPI, 10(1), 160. https://doi.org/10.3390/ani10010160
  2. Miller, A. B., Harris, P. A., Barker, V. D., & Adams, A. A. (2021). Short-term transport stress and supplementation alter immune function in aged horses. PloS one, 16(8), e0254139. https://doi.org/10.1371/journal.pone.02541393.
  3. Schmidt, A., Möstl, E., Wehnert, C., Aurich, J., Müller, J., & Aurich, C. (2010). Cortisol release and heart rate variability in horses during road transport. Hormones and Behavior, 57(2), 209–215. https://doi.org/10.1016/j.yhbeh.2009.11.003
  4. Tateo, A., Padalino, B., Boccaccio, M., Maggiolino, A., & Centoducati, P. (2012). Transport stress in horses: Effects of two different distances. Journal of Veterinary Behavior, 7(1), 33–42. https://doi.org/10.1016/j.jveb.2011.04.007

Amanda A. Adams

PhD

Amanda A. Adams, PhD, is an associate professor and a Mars Equestrian Fellow at the University of Kentucky Gluck Equine Research Center. She’s authored 40+ peer-reviewed scientific publications and presented her research at more than 40 national and international scientific meetings. Her research interests include the geriatric horse’s immune system; adiposity’s effects on horses’ inflammatory responses, particularly in EMS horses; and the mechanisms responsible for and pathways involved in EMS to identify potential treatments that target both the inflammatory and metabolic component of the disease.

Erica Jacquay

MSc

Erica Jacquay, MSc, is a PhD student and the first Mars Equestrian Scholar in the Department of Veterinary Science at the University of Kentucky working under Amanda Adams, PhD. Erica earned her BS in animal science from Virginia Tech and her MS from Kansas State, with an emphasis on equine reproductive physiology. She’s worked in various facets of the equine industry, including training dressage horses, working on a large sport horse breeding farm, and working in a veterinary diagnostic laboratory. Her research program focuses on equine transportation, with specific aims to evaluate the impact of short-term transportation on stress and immune function in horses.