Shoes: What New Heel Movement Research Shows

Every horse that leaves the farrier's crossties in a fresh set of shoes has traded something for the protection and grip it gained. The trade is small, measured in fractions of a millimeter at the back of the foot, and most owners never see it. A study published online in the Equine Veterinary Journal on October 11 puts a number on it, and in doing so it tests one of the more popular assumptions in the modern show barn: that a glue-on shoe lets the hoof behave more like a bare one.

The research comes from the Virginia-Maryland College of Veterinary Medicine in Blacksburg, Virginia. Fabian Jimenez Roa and colleagues, with Christopher Byron as the project's advisor and Travis Burns, the teaching hospital's chief of farrier services, on the team, fitted 15 healthy horses with three conditions in turn: barefoot, indirect glue-on fabric cuff shoes, and conventional aluminum nail-on shoes. A displacement sensor fixed across the heels of one forelimb recorded how far the heels moved as each horse walked and trotted on hard asphalt and on soft arena footing.

What the Sensor Recorded

The headline result confirms what farriers have long suspected. Heel movement was significantly greater barefoot than in either shoe (p < 0.0001). At the trot, the bare heels moved a mean of 3.29 mm (0.13 in). The glue-on shoe allowed 2.56 mm (0.10 in), and the nail-on shoe 2.12 mm (0.08 in). Worked out from those published means, the nailed shoe took away roughly 36 percent of the barefoot movement at the trot, and the glue-on roughly 22 percent.

The gap between the two shoes is real, and it is narrow. At the trot, the glue-on allowed more heel movement than the nail-on (P = 0.0005, according to the thesis abstract filed with Virginia Tech). At the walk, the same comparison was not significant (P = 0.1742). The trot difference itself comes to 0.44 mm (0.02 in).

Both shoes restricted the heel. The glue-on simply restricted it less, and only at the trot.

Why should a hunter or jumper owner care about fractions of a millimeter? The authors frame heel movement as critical to shock absorption and to vascular perfusion of the equine digit. A group at the Equine Research Institute of the Japan Racing Association opened its own 2010 study with the long-standing suggestion that heel expansion during the stance phase reduces concussion at impact and helps pump blood into the hoof.

The Word "Glue-On" Covers Too Much

The barn conversation tends to treat glue-on as a single category, and a gentler one. The literature does not support that shorthand. In that 2010 study, Yoshihara and colleagues at the Japan Racing Association put seven Thoroughbreds on a treadmill in plain aluminum shoes, attached first with glue and later with nails. Total heel movement was lower with the glued shoe at the walk and trot in all limbs, at the canter in the leading forelimb and both hind limbs, and at the gallop in both hind limbs. Their conclusion was blunt: gluing restricted heel movement.

A follow-up from the same institute, published in the Journal of Equine Veterinary Science in 2022, tested newer designs. Flexible polyurethane glue-on shoes produced no significant difference in heel movement from nailed shoes at any gait. A Hanton-type glue-on shoe, which uses two side clips for the adhesive, reduced heel expansion by 14 percent at the trot and increased contraction by 11 percent, with no difference in total movement. Read together with the Virginia result, the pattern is consistent. What governs the heel is how firmly, and where, the shoe is fixed to it, and the adhesive is only one way of fixing it.

Nails follow the same rule. In a 2023 cadaver study in Animals, Dahl and colleagues at the University of California, Davis, with a coauthor from Sussex Equine Hospital in England, loaded limbs to simulate the walk, trot, and canter with nails placed at the toe only, at the toe and quarters, or all the way back to the heel. Nails placed behind the quarters decreased heel expansion (p < 0.001). At Ghent University in Belgium, Brunsting and colleagues compared eight barefoot horses with the same horses in a conventional toe-clipped shoe and in a new shoe with a split toe. On a treadmill at the walk, trot, and canter, the conventional shoe allowed significantly less heel expansion in every gait (P ≤ 0.001). The split-toe shoe did not differ significantly from barefoot. Their paper appeared in The Veterinary Journal in 2019.

The Case for the Nailed Shoe

None of this makes the conventional shoe a mistake, and the strongest argument for it deserves a fair hearing. The Virginia team's own summary states that shoes are necessary for protection and performance. A show jumper that turns tightly on varied footing and competes in studs depends on an attachment that stays put through a full shoeing cycle, and for many horses that remains a nailed shoe. Less than half a millimeter of heel movement at the trot is a modest price for a shoe that holds.

The evidence also has clear limits. The Virginia sensor had no absolute zero baseline, so it could not separate expansion from contraction. Low heels in some horses prevented recordings on soft footing, which reduced statistical power. Fifteen healthy horses were tested at the walk and trot, with no canter and no fence. No study cited here followed horses long enough to link reduced heel movement to lameness. The Ghent authors wrote only that the restriction "may" harm orthopedic health, and the Japanese group said only that gluing suggested "possible" interference with shock absorption and blood flow.

Older work at the Swedish University of Agricultural Sciences in Uppsala adds a further variable. Roepstorff and colleagues reported in 2001 that increased pressure on the frog and sole increased heel expansion, though some expansion still occurred without that support. The shoe is one input among several, and frog support and nail pattern both shape the same few millimeters.

What Owners Should Take to the Farrier

The useful conclusion is narrower than the marketing around either system, and more practical. Where a farrier recommends a glue-on for a specific hoof problem, the Virginia data show that one fabric cuff system leaves the heel somewhat freer at the trot. It does not return the foot to barefoot, and a rigid glue-on fixed hard to the heels may restrict it more than nails do. The better question for a farrier is how a given package fixes the back of the foot: where the last nail sits, how far the cuff or adhesive extends, and whether the frog is carrying any load.

The research gap belongs to the sport. Every heel movement study cited here measured horses on the flat, on a treadmill, on asphalt and arena footing, or in a loading machine. None measured a horse landing from a fence. Until that work exists, the most defensible position is to treat every shoeing choice as a deliberate cost paid for a specific benefit, and to ask what the benefit is before the first nail goes in.