“When riders tighten the reins, there’s that total amount of force they’re applying that’s got to go somewhere, and it all just depends on where you’re putting it,” said Tracy Bye, MSc, of the University Centre Bishop Burton, in Yorkshire, the U.K.
“That amount of force on the reins is roughly the same, and it could go onto a bit or onto the nose or onto the top of the head,” she said. “We didn’t measure rein tension here, but we saw the pressures resulting from that tension. And we can’t say that bitless bridles are kinder to the horse.”
Comparing Forces and Head and Neck Positions With Snaffles, Cross-Unders, and Side-Pulls
Inspired by a conference study on noseband tightness in competition horses, Bye and her student Nina Robinson observed five university riding horses each working with three kinds of bridles: a snaffle-bit bridle with a simple cavesson noseband, a cross-under bitless bridle, and a side-pull bitless bridle. They fitted nosebands according to the “two-finger” rule for the snaffle-bit bridle and to the manufacturer’s instructions for the two bitless bridles, as measured by a noseband taper gauge. For the cross-under, this meant a one-finger space and for the side-pull less than a one-finger space.
The researchers fitted pressure sensors under each bridle’s headpiece and noseband, and the horses worked in an arena for 30 minutes per day for three days in a row in each kind of bridle, ridden by the same rider (for each horse).
They found that the average pressure on the nasal plane (over a length of 11 centimeters) was 65% higher with a side-pull bitless bridle compared to a snaffle-bit bridle. With the cross-under bitless bridle, average pressure was about 11% higher than with the snaffle. (Pressures in this design might have been higher under the jaw, which the researchers said they didn’t study.)
Peak pressures on the nasal bones were 147% higher with the side-pull and 109% higher with the cross-under compared to the snaffle, they said.
In all cases—including the snaffle-bit bridle with noseband—pressures were frequently as high as recommended pressures for tourniquet use in human medicine, the researchers said.
In the bitless bridles, pressures—especially the intermittent peak pressures—were particularly high, they said, but weren’t necessarily causing damage.
“These are pressures that could be potentially damaging to horses—but only if they’re maintained over those thresholds for a sustained period of time,” Bye said. “That’s something we don’t know yet.”
They also noted that the horses tended to carry their heads higher with their necks more extended when ridden with a cross-under bitless bridle, the team reported. Such a position could contribute to back pain and poor performance, they said.
Despite all these differences, they found no significant changes in poll pressure among the three bridle types.
“Many riders choose bitless bridles in an attempt to overcome training issues, which manifest as conflict behaviors in response to bit pressure,” Bye said. “No piece of equipment is the sole solution to these problems, as the pressures from the rein do not disappear when you change the bridle; they just move to other facial structures. The real solution has to be educating riders and supporting them to develop the skills to communicate with their horses effectively.”
The study, “Noseband and poll pressures underneath bitted and bitless bridles and the effects on equine locomotion,” was published in the Journal of Veterinary Behavior’s July-August 2021 edition.