Transport and Exercise’s Effects on Horses’ Microflora
Stress triggers clear behavioral and physiological responses in horses. Stress not only leads to the development of stereotypical behaviors and high cortisol (the stress hormone) levels but also disrupts the horse’s gastrointestinal (GI) system, especially the microflora that reside there.

Because it is impossible to eliminate all stress in our horses’ lives, Kyla Szemplinski, a 2018 master’s degree graduate of Tarleton State University, in Stephenville, Texas, sought to find out how common stressors—transport and exercise, which we can theoretically control-affect the equine microbiome. She shared her findings at the 2019 Equine Science Society Symposium, held June 3-6 in Asheville, North Carolina. Her thesis committee included Trinette Jones, PhD; Kimberly Guay, PhD; Brandon Smith, PhD; and Jeffrey Brady, PhD.

In her work, Szemplinski studied four drylot-kept adult Quarter Horses consuming free-choice grass (coastal Bermuda grass) hay and a concentrate grain designed for horses of all ages and activity levels. During the transport phase, she hauled each horse in a 16-foot aluminum trailer for 15 minutes, three hours, and six hours, with seven days between each trip. In the following exercise phase, she free-longed three of the four horses at low, medium, and high intensity, with seven days between each exercise session.

Szemplinski collected fecal samples from each horse two hours after its morning meal and 48 hours post-transport or -exercise. She used these samples to assess the horses’ microflora DNA and found that:

  • Exercise did not affect microflora diversity.
  • Bacteroidetes (bacteria that help break down cellulose and pectins in plant cell walls) populations increased post-transport.
  • Firmicutes (which help produce amino acids) decreased post-transport.

The latter two changes were most significant when horses were trailered for at least six hours.

“Further research with longer transport time (more than six hours) and more intense exercise stress are needed to further explore how these two common stressors affect the microflora populations,” Szemplinski said.

In the meantime, owners can be cognizant of transport’s effect and exercise’s potential effect on their horses’ GI systems. Watch for signs of loose stool or gastrointestinal upset, which could indicate microflora disruption and might warrant a call to your veterinarian.