Pin firing is a centuries-old veterinary technique in which heated metal needles are pressed into a horse’s leg to deliberately damage tissue, with the goal of triggering an inflammatory healing response in an injured tendon, ligament, or bone underneath. The procedure has been one of the most debated practices in equine medicine, and major veterinary organizations now oppose it. The American Association of Equine Practitioners states it finds “no scientific evidence to validate its use in the horse.”
How the Procedure Works
During pin firing, a veterinarian heats a thin metal instrument, often resembling a pointed probe, and inserts or presses it into the skin and underlying tissue of the horse’s leg in a pattern of small puncture burns. The horse is placed under general anesthesia or heavy sedation. The burns are typically arranged in rows or grids over the affected area, leaving a distinctive dotted pattern of scars on the leg.
Variations exist. “Point firing” or “pin firing” uses the tip of the instrument to create individual puncture wounds directly into or near an injured structure. “Bar firing” or “line firing” drags the heated instrument across the skin in lines over the injured area. Some practitioners use electrosurgical tools or even liquid nitrogen instead of a traditional heated iron, but the underlying principle is the same: deliberate tissue destruction as a form of treatment.
The Theory Behind It
Pin firing rests on two ideas, neither of which has held up well under modern scrutiny. The first is called counter-irritation. The logic goes like this: a chronic injury that won’t heal on its own might be “stuck” in a state of low-grade inflammation that isn’t productive. By creating a fresh, acute injury on top of or next to the old one, the body mounts a vigorous new inflammatory response with increased blood flow, and that wave of healing activity supposedly carries the original injury along with it.
The second theory is more mechanical. Scar tissue that forms in response to the burns could act as a kind of internal bandage, physically tightening and reinforcing the weakened tendon or ligament. Proponents sometimes describe this as “toughening up” the leg. In practice, though, scar tissue is structurally inferior to the organized collagen fibers it replaces, which makes this rationale hard to defend from a tissue-biology standpoint.
Conditions Historically Treated
Pin firing has been used most commonly in racehorses, particularly for injuries to the superficial digital flexor tendon (the tendon running down the back of the lower leg, commonly called a “bowed tendon” when it’s injured). It has also been applied to splints, curbs, and other repetitive strain injuries of the cannon bone and hock area. In cases involving bone, such as incomplete stress fractures that keep flaring up when the horse returns to training, some veterinary texts have noted pin firing as a way to encourage more aggressive callus formation at the fracture site. This is one of the few scenarios where older literature reported a reasonable clinical outcome.
In American racing, pin firing was historically bundled with a standard rehabilitation program: the procedure itself, followed by months of controlled exercise or turnout in a large pasture. Because the recovery protocol always included extended rest, critics have long argued that the rest, not the firing, was the real reason horses improved.
What It Does to the Tissue
The burns kill cells in the treated tissue and damage the collagen fibers that give tendons and ligaments their strength. The body responds with wound healing: inflammation, new blood vessel growth, and eventually scar tissue. This scar tissue is disorganized compared to healthy tendon. It’s stiffer and less elastic, which can change the way the structure absorbs force during movement.
On the surface, pin firing leaves permanent cosmetic marks. The characteristic grid of small round scars is immediately recognizable, and the hair that regrows over the burn sites often comes in white. For owners and trainers in competitive disciplines, these visible marks carry a stigma, since they signal the horse has had a significant injury and a controversial treatment.
Why Veterinary Organizations Oppose It
The AAEP’s position, most recently revised in 2025, is unambiguous: with effective, science-based treatments now available for musculoskeletal conditions, the organization does not support the use of thermocautery or pin firing. No controlled clinical trials have demonstrated that firing produces better outcomes than rest and rehabilitation alone.
The Australian Veterinary Association takes a similar position, emphasizing that the defining characteristic of all firing methods is “deliberate damage to tissue, often normal healthy tissue, as a treatment per se for lameness.” The concern is straightforward: you’re injuring a horse in the hope of healing it, and the evidence that this works is largely anecdotal.
The Fédération Equestre Internationale (FEI), which governs international equestrian sport, prohibits horses from competing if they show evidence of recent firing, including signs of inflammation, hypersensitivity, or reduced sensation at the site. While this isn’t an outright ban on the procedure itself, it effectively bars recently fired horses from FEI competition.
Modern Alternatives
Treatment of tendon injuries in horses has changed dramatically over the past two decades. Controlled rehabilitation, where the horse follows a structured program of gradually increasing exercise, remains the foundation. But biological therapies have added genuinely new tools.
Platelet-rich plasma (PRP) concentrates the horse’s own blood platelets and growth factors and injects them directly into the injured tendon. Mesenchymal stem cells, harvested from the horse’s bone marrow or fat tissue, can be injected into the core of a tendon lesion. Research published in the Journal of the American Veterinary Medical Association has found that stem cell treatment leads to increased return-to-performance rates and reduced reinjury rates compared to controlled rehabilitation alone. Horses treated with stem cells also showed improved tendon architecture, with better-organized collagen fibers rather than the disorganized scar tissue that forms after firing.
Extracorporeal shockwave therapy, therapeutic ultrasound, and injectable joint supplements like hyaluronic acid and polysulfated glycosaminoglycans are also widely used. These approaches share a common advantage over pin firing: they aim to improve the quality of the healed tissue rather than simply provoking more inflammation.
Why It Still Happens
Despite the professional consensus against it, pin firing hasn’t completely disappeared, particularly in certain segments of the racing industry. Tradition plays a role. Trainers who have used firing for decades point to horses that returned to racing successfully, and that firsthand experience can outweigh position statements from veterinary organizations. The procedure is also relatively inexpensive compared to stem cell therapy or PRP, which require specialized equipment and laboratory processing.
There’s also a confounding factor that makes the practice hard to evaluate from the barn aisle. Because pin firing always comes with enforced time off (weeks of bandaging and wound care, followed by months of turnout), horses do often improve afterward. But separating the benefit of rest from the benefit of the burns themselves is exactly the kind of question that requires a controlled study, and no such study has produced evidence in firing’s favor.