In her study, Price split 20 riding horses into five groups of four. Each group received a different starch-to-fat ratio in their diet, ranging from 7.1% to 14.3% starch. Throughout the 21-day period, all horses were fed twice daily, housed individually in stalls, and ridden in regular collegiate lessons (beginner to advanced equitation and hunter/jumper classes).
Price asked riders and instructors that were blind to the horses’ treatment groups to complete a behavior survey after each lesson. They evaluated each horses’ behavior when being caught, led, and groomed, as well as his energy levels while ridden, reaction to leg aids, relaxation, submission, and more. Price took blood samples on the first and last days of the trial after the horses had fasted for 12 hours.
She found that:
- The diets had no significant effects on horses’ body weight or body condition score. This was expected, said Price, as all treatment groups were balanced by body weight.
- Horses on high-starch, low-fat diets had higher behavior reactivity scores from both instructors and riders.
- Horses on low-starch diets became better behaved over time, and vice versa.
- Diet type didn’t significantly affect insulin sensitivity, whereas an increased number of workouts did. This means diet composition might not influence insulin sensitivity as significantly if horses are in heavy exercise, she explained.
Overall, “feeding high-starch, low-fat grain mixes can negatively influence the behavior of performance horses under saddle,” Price said.