Patricia M. Graham-Thiers, PhD, and a team of Virginia Intermont College researchers assigned 16 horses in light to moderate work to one of three groups: pasture turnout (P), stalled and exercised (E), or stalled with no exercise (S). During the 14-week study, horses in the P group roamed on approximately 100 acres of pasture, while horses in the S and E groups stayed in stalls during the day and were allowed access to a one-acre paddock at night.
The researchers exercised horses in the E group five days per week for one to two hours per day at the walk, trot, and canter. The team also used GPS units attached to the horses’ halters to estimate the distance each horse traveled in a 24-hour span at intervals throughout the study period.
The team put each horse through a standardized exercise test (SET, lasting 20 minutes, with consistent increments of walk, trot, canter and hand-gallop work, and a 10-minute cool down period) at the beginning and end of the 14-week study. Researchers took blood samples and rectal temperatures before the SET, at peak exercise, and during recovery; they recorded horses’ heart rates at intervals throughout the SET.
Also before and after the treatment protocol, researchers evaluated each horse’s body fat via an ultrasound of rump fat (to estimate total body fat percentage) and took radiographs of one of each horse’s cannon bones to measure bone mineral content–an important determinant of bone strength. Additionally, the team evaluated horses’ weights and body condition scores every other week during the study.
Key findings included:
- Rump fat measurements and bone mineral content did not differ between treatments at the start of the study; however, P horses had greater bone mineral content compared S and E horses at the end of the study.
- At one minute into recovery after the SET, S horses showed a 63% increase in heart rate from start to finish of the treatment, whereas P horses showed minimal difference (4%) and E horses’ heart rates decreased (-21%).
- S horses’ rectal temperatures were higher at peak exercise, and their plasma lactate and rectal temperatures were significantly greater during the 10 minute recovery compared to the E and P horses. The team did not observe any other differences in blood parameters.
- Based on GPS readings, P horses traveled a greater distance on a daily basis compared to the E or S horses. Interestingly, the team noted, the P horses even traveled farther than the E horses during exercise days.
The team concluded that horses on stall rest for 14 weeks lost fitness, as indicated by the increase in heart rate and blood lactate levels after the final SET. But more importantly, they noted, pastured horses were able to maintain a similar level of fitness as the stalled, exercised horses in addition to having greater bone mineral content at the end of the study.
Graham-Thiers concluded, “Letting horses be horses—as in putting them in their natural setting—allows them to maintain fitness better, which may make their transition back to competition easier and likely more successful.”
The study, “Improved Ability to Maintain Fitness in Horses During Large Pasture Turnout,” was published in August in the Journal of Equine Veterinary Science.