By Christa Lesté-Lasserre
Nobody knows where the “two-finger rule” for fitting bridle nosebands came from. But according to results of the latest study on noseband tightness, it makes sense.
When a rider can easily slip two fingers between a horse’s front nasal bones and the noseband, pressure levels around the horse’s face are generally acceptable. But as it gets more difficult to squeeze even one finger under the noseband at that same place, pressure on the horse increases exponentially, reaching heights that are technically inhumane, a leading equitation scientist said.
“Our pressure readings at half-finger and zero-finger tightness literally went off the screen, and we thought our system was malfunctioning,” said Orla Doherty, MVB, MSc, PhD, MRCVS, of the University of Limerick, in Ireland, and hon. president of the International Society for Equitation Scientist (ISES).
“We kept repeating the experiment, thinking, ‘We can’t possibly be subjecting live animals to that kind of pressure!’” Doherty told The Horse. “But actually, we are. Every day and at every competition.”
In their study, Doherty and her fellow researchers equipped a cadaver horse head with a standard dressage noseband as well as pressure sensors in various places along the bone and soft tissue under the noseband. Working with a cadaver head allowed them to more easily study the anatomical structures affected by the nosebands, she said. Further, it was the only humane way to carry out the study.
“Based on inquiries, we did not believe we would get ethics approval to carry out this study on live animals—to test them in a laboratory being subjected to the exact same pressures they’re getting in riding arenas on a regular basis,” said Doherty. She presented her research topic during the 15th annual ISES conference, held Aug. 19-21 in Guelph, Ontario, Canada.
Although researchers have studied noseband tightness before, this new investigation with a cadaver head gave the team more detailed insight into how pressure at individual sites along the horse’s face changes as the noseband tightens, hole by hole, she said. For example, they confirmed pressure is much higher on the bones than on the softer tissues, which can compress in response to pressure.
However, they noted that when they passed from one finger tightness toward zero finger tightness, pressure levels multiplied in an exponential fashion—possibly because the soft tissues reached their maximum level of compression, and there was no way for the horse’s facial structures to cope with the pressure.
What’s more, the shape of the horse’s nose at the area under the noseband makes it particularly susceptible to high pressures, said Doherty. The left and right nasal bones create two ridges running down toward the nostrils, spaced a few centimeters apart, with a slight dip in the center. Between the two ridges is soft tissue.
It’s the width and roundness of these bony ridges that make the difference, biomechanically, Doherty explained. Although a horse’s nose itself is fairly wide, these bony ridges are thin, having a very small radius in the circle of the rounded edge that takes the brunt of the noseband’s pressure. As the radius of curvature of any structure gets smaller, pressure levels shoot up because they’re concentrated on a smaller area—it’s just the law of physics, she said.
“These are hard tissues with very small radial measurements that just can’t offset the kind of pressure they’re getting subjected to,” she said. It’s somewhat akin to tightening and leaving a strap on a human’s hand, across the knuckles with extremely high pressures—except the knuckle bones actually have a wider radius, resulting in less pressure than what’s seen in horses’ nasal bones, she said.
“These are hard bumps that can’t move or squish or flatten out to distribute the pressure in any way,” Doherty said.
Click here to see more...