Abigail Reilly, an undergraduate at Centenary University, in Hackettstown, New Jersey, along with assistant professor of equine studies Jesslyn Bryk-Lucy, DVM, recently conducted a study investigating this topic. Reilly presented their findings at the Equine Science Society’s 2021 virtual symposium.

The Association Between Tendons, Turnout, and Fitness

Horses’ tendons adapt to changes in their biomechanical environment—basically, they restructure in response to movement, said Reilly. Research has shown that this process occurs more rapidly under conditions such as turnout.

Getting into the physiology, she explained that “thick collagen fibers provide tensile strength to the tendons but don’t have much give. They are formed under static conditions. Thin collagen fibers allow elasticity of the tendons—these thin fibers are formed with exercise. Exercised and pastured horses have more thin fibers, meaning their tendons are more equipped to adapt to their movements.”

Pastured and exercised horses also tend to have greater fitness than stalled horses, and studies show fitness can reduce soft tissue injury likelihood in humans and horses alike.

A common way to define fitness and analyze injury occurrence, said Reilly, is by calculating acute to chronic workload ratio (the difference between baseline workload and intense training days). A low ratio means a mild change in workload and less chance of injury, while a high ratio indicates big spikes in workload, which is when injuries often occur.

“I was curious if this principle applied to nonelite horses with varying amounts of turnout,” she said. “If a horse has low chronic workload, like a stalled horse, they will have a lower baseline fitness. When these horses are asked to perform, there will be a large spike in the ratio no matter the intensity of work. If horses are out on pasture, they’re maintaining a higher chronic workload because they’re walking, grazing, and being a horse. When they are asked to perform and have a spike in the ratio, they already have this baseline fitness, and the difference between the acute and chronic workload is less.”

A Study of Lesson Horses

Reilly hypothesized that horses with more than 12 hours of turnout per day would have significantly less incidence of soft tissue injuries than horses turned out for less than 12 hours because of their increased baseline fitness. Studies have shown that 12 hours is enough time to cause a physiological change in response to exercise.

She and Bryk-Lucy performed a retrospective cohort study of 146 lesson horses averaging 17 years of age at Centenary University’s equestrian center from 2014 to 2020. They examined all horses’ medical records over those six years to identify if and when they had experienced a soft tissue injury. Bryk-Lucy and another resident veterinarian had diagnosed all injuries using either ultrasound, MRI, or process of elimination. All horses were managed similarly, had consistent workloads appropriate for their riding level, and exercised on the same arena surfaces. Reilly said they did, indeed, find a significant difference between soft tissue injury incidence between the two groups. Specifically:

• Of 57 horses with more than 12 hours of turnout per day, 14 (25%) sustained soft tissue injuries.
• Of 89 horses with less than 12 hours of turnout per day, 45 (51%) sustained soft tissue injuries.

“These results suggest an inverse relationship between length of paddock turnout and risk of soft tissue injuries in nonelite horses,” said Reilly. “They also support that turnout maintains a baseline level of fitness so horses can better handle acute spikes in workloads and, thus, have reduced risk of injury.”

Horse owners can apply these findings by offering as much turnout as is possible and appropriate for their horses.

If you’re interested in viewing presentations from the 2021 Equine Science Society Virtual Symposium, you can register for the Symposium until Aug. 2, 2021, and recordings are available for viewing until Sept. 3, 2021.