Heart Rate Variability to Detect Equine Transport Stress

A fear of flying can lead to such extreme stress that many people find themselves unable to board an airplane. While horses aren't likely to show a true "fear of flying," they are undoubtedly stressed by air travel, according to a recently completed study of in-flight horses.

In addition to revealing stress levels of horses during air and road transport, the study led by Hajime Ohmura, DVM, PhD, of the Japan Racing Association's Equine Research Institute, also provided the researchers an opportunity to better evaluate the usefulness of heart rate variability (HRV) in analyzing equine stress.

Using an electrocardiogram, Ohmura et al. measured heart rate and heart rate variability of six healthy Warmblood horses during:

  • A 24-hour pre-transportation quarantine;
  • A 4 ½-hour trailer ride;
  • A 5-hour waiting period after the trailer ride; and
  • An 11-hour flight.

The team found that both air travel and road travel both caused major spikes in the heart rate of study horses compared to rest in quarantine. They also learned that the HRV (variations between heart rates) could be an even more "sensitive" indicator of the kind of stress that horses experience during transport, Ohmura said. HRV determines how much the beat-to-beat interval (the heart rate) changes in a given amount of time.

Heart rate readings alone did not provide reliable information about the horses' stress levels, Ohmura reported in his study, as it had certain peaks and lulls that might suggest that the horse wasn't stressed at certain times of transport. For example, the six Warmblood horses used in the current study had very high heart rates during the first hour of road transportation, but then their heart rates dropped dramatically as though they had just gotten used to the travel.

Study author James H. Jones, PhD, DVM, of the school of veterinary medicine at the University of California-Davis in Davis, California, relayed, "We could detect stress from the HRV pattern throughout travel, compared to stall rest. In fact, in a previous study we noted that there is a modest occurrence of (ground) transport stress related to respiratory disease (in horses that travel for) up to about 10-12 hours. After that, the occurrence of 'shipping fever' shoots up dramatically. That seems to be a key duration for lots of horses."

Air transportation was no less stressful, despite the horses appearing calm during an uneventful 11-hour flight from Belgium to Japan, Jones added. HRV readings confirmed high levels of stress for these equine passengers. "Horses do not seem to like being confined in an air stall in a noisy bumpy environment," Jones said.

It's too soon to compare the kinds of stress horses experience between air and road transport, Jones added. More data on air transport could lead to a better understanding of this particular source of stress.

The study, "Changes in heart rate and heart rate variability during transportation of horses by road and air," appeared in the April 2012 issue of the American Journal of Veterinary Research. The abstract is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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