Reilly wants to make better shoes to treat various forms of lameness, much as a podiatrist crafts orthotics for humans. His prime target is laminitis, a poorly understood, crippling disease that has plagued horses - and their owners - for centuries. The illness involves painful inflammation and, in severe cases, separation of the hoof from the foot. After colic, it is the second most common reason that horses are euthanized, as happened with its most famous victim, Barbaro.
"Every year when the Triple Crown comes around, I'm thinking to myself, 'What would I do differently if I was presented with another challenge?' " said Reilly, who helped care for the 2006 Kentucky Derby winner. "It's a yearly reminder of the need to get better."
Reilly has a powerful frame and the chipped fingernail or two one might expect from someone who works with steel. He has two forges in his shop at the New Bolton Center, the vet school's campus in Kennett Square, where he is skilled at hammering a straight piece of metal into a custom-fitted shoe.
But he is just as much a historian and researcher, seeking to improve his trade both through modern technology and by studying old horseshoes from the 19th century - in hope of rediscovering expertise from the days when the horse was a primary engine of the U.S. economy.
Penn's vet school is one of the few with a farrier on staff, allowing Reilly to provide a bridge between science and the barn, said Jeffrey Thomason, a professor at the Ontario Veterinary College at the University of Guelph in Canada.
Reilly's aim is to make a shoe to better ease pressure on the hooves of a lame horse, allowing it to recover.
Farriers have been trying new shoes for centuries, but it is hard to tell if you are alleviating something unless you can measure it. So several years ago, Reilly decided to start doing just that.
Joseph, the 1,200-pound horse with the crooked legs, waited as Reilly bent one leg back and fitted the hoof with a green sheet of plastic - actually a sandwich of two sheets, each lined with rows of semiconductive ink.
The green film was connected by cable to a small box called a data logger, which recorded the force exerted at 1,000 locations on the hoof.
The system, made by Tekscan Inc. of Boston, tracks force by measuring electrical resistance, company officials said. The harder the rows of ink are pressed together at any one point, the lower the resistance.
The company makes similar systems for humans, which are used in medicine and academia and by shoe companies. Tekscan started making horse-size sensors at Reilly's request; horseshoes hold them in place.
Reilly has evaluated more than 30 horses so far. Often, the results are not what he expects.
With Joseph, a Morgan-cross horse, his front ankles rolled outward, and the outer edges of the hooves were shorter than the inner edges. Reilly predicted that the pressure might be greater on the outer portion.
But when he plugged the data into a laptop and brought a diagram of the hoof to up on the screen, he was surprised. The readings showed the forces were fairly evenly distributed, occasionally even higher on the inside edge.
"A little bit the opposite of what I was expecting to see," Reilly said. "This is what makes this stuff fun."
Traditionally, farriers and vets have gauged the effects of their treatments by watching to see if the horse limped. High-tech diagnostic tools, such as ultrasound and magnetic resonance imaging, are now also used.
But the advantage of the pressure-sensing film is that Reilly can measure horses on the move, on a variety of surfaces - pavement, dirt, synthetic pads. He plans to take readings from many more horses.
"We're still trying to define normal," he said.
Yet Reilly already is working on a prototype shoe for horses with laminitis, one that would ease pain with a springlike mechanism. He drew inspiration from vintage models in Penn's collection.
Some argue that horses are better off with no shoes at all, echoing the barefoot-running movement in people. Thomason, who studies horse biomechanics at Guelph, said that the practice works in some cases, but that if the horse is carrying a lot of weight, the hoof typically needs protection.
Shoe or no shoe, horses get laminitis, and usually the initial cause has nothing to do with the foot, said veterinarian Hannah Galantino-Homer, a Penn colleague of Reilly's.
The disease can be triggered by infections elsewhere in the body, such as the intestines, lungs, or uterus. This sets off an inflammatory cascade, causing the release of enzymes that can break down the sensitive tissue that connects hoof to foot.
"This is their weak link," Galantino-Homer said. "The foot has evolved so that it allows them to be the amazing athletes that they are, but it's also what brings them down."
Other causes include eating too much grass, which can lead to insulin resistance, she said. Laminitis can also be caused by severe overwork, but this is much less common, said Thomason, the biomechanics researcher.
Though the cause may not start with the foot, Reilly hopes he can solve the problem from that end. Unlike Barbaro, horses do sometimes recover from laminitis. If Reilly can redistribute the pressure on their hooves, he can buy them time to heal.
"I need and I expect to get better at this," Reilly said. "If I didn't have the expectation of doing better, it'd be a very depressing job."
Contact Tom Avril at 215-854-2430 or firstname.lastname@example.org.