As scientists discover more about the way a horse’s social life affects his behavior and, possibly, training, researchers find themselves in need of a reliable, efficient way to measure social hierarchy. Danish behavior scientists appear to have found the solution through a "limited resource test."

Observing how horses interact with each other in the field has historically been the most reliable method, Line Peerstrup Ahrendt, PhD, researcher in the department of animal health and bioscience at Aarhus University, said during a presentation at the 2012 International Society for Equitation Science conference. But you can’t just watch horses for a half an hour to see who assumes role of "leader." Social hierarchy among horses is complex; it’s not just about finding a single "herd leader," she said. And that’s why in order to get accurate results, field observation of a group of horses usually requires at least 15 hours over a five-day period, sitting in the grass with a clipboard, jotting down every detail of horses’ interactions with each other. And often, horses are so used to their hierarchy that their social interactions don’t give obvious clues, Ahrendt added.

To improve social hierarchy studies, Ahrendt and her colleagues have recently developed a more efficient system called the "limited resource test." By placing three bins of food in the group’s pasture, scientists can study the interactions among all the horses for as little as 80 minutes over a four-day period. And according to their research, the limited resource test is just as reliable as the much longer field observation method.

Her study involved a comparison of both methods with the same group of horses: 25 Warmblood geldings age 2 to 3 years old. They had been pastured together in a 19-acre field for two months–long enough to establish their social hierarchy, said to Ahrendt. The researchers recorded 180 interactions during the five-day, 15-hour field test. They recorded 163 observations during the four-day, 80-minute limited resource test. Ratio calculations were made to determine the hierarchy in both tests