“Numerous variables affect the interaction between the hoof and the ground surface, and any of these variables could contribute to an increased risk of injury in horses,” said Alexis Szpakowski, a recent bachelor of science graduate from the University of Guelph, in Ontario, Canada.
Those variables include not only the footing’s qualities but also the horse’s weight, the direction he’s going (straight or on a curve), the direction of turn, the lead he’s on, and multiple other factors, according to Szpakowski and her colleague Danielle Halucha, a master of science candidate also at the University of Guelph. Both scientists presented their work in separate presentations during the 15th annual conference of the International Society for Equitation Science (ISES), held Aug. 19-21, 2019, in Guelph.
When a hoof hits the ground, it doesn’t just touch and go, the researchers explained. It has an initial impact that causes the hoof to brake and experience internal vibrations that can extend up the limb. The hoof slides briefly before reaching a full stop with the horse’s mass centered over it. In a gallop, the horse’s entire body weight, multiplied in force due to the combination with speed, bears down fully on a single hoof during this midstance, which includes a push-off to propel the entire horse forward. As the body mass passes in front of the limb, the hoof rolls forward and over the tip in what’s known as the “breakover,” before lifting off the surface.
“In each of these phases, the hoof experiences different forces and accelerations, and each of them is associated with different risk factors for injury,” said Halucha.
It’s very difficult to identify the mechanical causes of injury, however, she added. With so many factors involved, concerning both the horse and the environment (surface and conditions), recognizing the links between injuries and the many forces affecting the various phases of contact between hoof and surface is a daunting task.
“We know that racehorses experience major force on their limbs, reaching 2.5 times their body weight on a single hoof during certain phases of stance at the gallop,” Halucha said. “In my study we saw that strain can vary considerably from one limb to the other, depending on which lead the horse is on and if he’s galloping on a straight line or a curve.”
As for Szpakowski, she said she found lower limb forces in a soft sand arena than a hard-packed sand arena—with the exception of heavier horses. Bigger horses actually had higher midstance forces in soft sand than hard-packed sand.
“We saw that both size and surface affect loading at all phases of the stance,” she said. “These factors work independently and in combination to cause changes in the limb loading, with the most obvious finding in my study being that heavier horses experience greater forces on soft sand at midstance whereas, for the lighter horses, the harder sand creates this effect.”
In each of the two studies, the scientists used accelerometers and strain gauges attached to the front hooves of working horses. Szpakowski compared measurements between 10 horses ridden at a trot under the same rider in two conditions: a soft sand outdoor arena and a hard sand indoor arena. She recruited horses of varying breeds and weights, ranging from 356 kilograms (783 pounds) to 673 kilograms (1,480 pounds). Meanwhile, Halucha looked at 10 Thoroughbreds (2- and 3-year-olds and one 10-year-old) galloping a lap on a dirt track.
“Loading definitely differs between left and right limbs depending on the curve as well as the lead,” Halucha explained. “We went into the study expecting to find a significant effect of curve, which we did, but we also found one for (front) lead (leg). This needs to be kept in mind when making the suggestion that a horse just ‘took a bad step.’ There’s clearly more to it than that.”
More detailed analysis revealed that the younger horses tended to switch leads frequently, whereas the 10-year-old horse did not, she added.
While the studies were preliminary and could not lead to specific guidelines, they helped “contribute to the growing body of knowledge” about footing and injury risk, said Szpakowski.
“Our findings showed hoof-surface mechanical interactions that aren’t immediately intuitive, and being aware of this could be a key factor in injury prevention,” she said.