A horse’s puncture wound might be caused by a rusty wire or nail sticking out shoulder-high from a pole in the stall or shelter—some forgotten and overlooked, left over from when the structure was built decades ago.

Or it might be a tree branch that impales the horse’s head or chest during a major thunderstorm.

Alternately, it could be something as seemingly innocuous as an old hairpin, a lost sewing needle, or even a half-unbent paperclip—if it finds just the right accident-prone horse to dig into.

Whatever the puncturing object is, what’s important now is managing the wound it has created and the debris and pathogens (disease-causing organisms) it has introduced. Deep and often burrowing into delicate internal structures, yet frequently undetected or even healed on the surface before you notice them, puncture wounds distinguish themselves as a complicated kind of injury.

Here 10 things you might not know about skin puncture wounds in horses. With this knowledge you can be prepared to recognize, manage, and prevent these injuries in your horse.

1. Puncture Wounds are Master Deceivers.

Puncture wounds in horses are unique in that externally they’re a small wound, but they run much deeper within the body, says Gemma Pearson, BVMS, Cert. AVP (EM), MScR, CCAB, PhD, MRCVS, director of equine behavior at The Horse Trust and lecturer at The University of Edinburgh’s Royal (Dick) School of Veterinary Studies, in Scotland.

Therefore, they might seem minor—especially compared to lacerations that rip off pieces of skin. But they’re not.

“With a really big laceration, you can see where the wound’s gone usually, whereas with a puncture wound, because the entry hole is very small, it’s hard to see,” Pearson says, adding that she’s seen puncture wounds “pretty much on every part of the body.”

In fact, puncture wounds can hide the potential for mass destruction far below that tiny skin wound, says Nolton Pattio, VMD, official veterinarian for the California Horse Racing Board, in Sacramento.

“A sharp object penetrates the skin and goes to a certain depth and direction, but how deep, and where?” Pattio says. “And therein lies what makes a puncture wound so different. It can be difficult to detect and know the extent of the damage.”

2. The Worst Puncture Wounds are Often the Narrowest.

It might seem like the scariest puncture wounds are the biggest ones—the kinds where there’s an entire tree branch breaching a horse’s side, for example. Certainly, those present a lot of risks, as they can damage multiple structures significantly, as well as cause hemorrhaging if they hit a major blood vessel, says Pearson.

But it’s the smaller puncture wounds that end up being the most treacherous, she adds.

“They’re so small, they’re often underestimated. You can have a gash the size of my arm and it looks really scary, but a lot of the time it’s the small ones that I worry about.”

Worse, a tiny skin wound can quickly close, well before the tissues underneath have healed—not only hiding the problem but also trapping in any kinds of foreign debris and/or infection, says Marcos Rosa, DVM, MSc, of the Federal Rural University of Rio de Janeiro, in Brazil.  

“These are definitely a multi-issue challenge, since we have no idea of the damage until we evaluate the whole lesion,” Rosa says.

3. Puncture Wounds Can Penetrate Protected Internal Structures.

Wood, metal, hard plastics, and any other hard, pointed material can pierce bodily tissues, traversing multiple structures along the way, says Pattio.

Veterinarians need to know long the penetrating object was and which structures it might have perforated to be able to treat it correctly. “How long was that object, and where did it go?” he says. “Did it stop at the skin? Did it just go in a few centimeters? Did it get into a bone? Did it work into a blood vessel? And what’s really worrying is when it gets into a body cavity like a joint, the thorax, or the abdomen.”

These body cavities aren’t meant to be disrupted, Pattio explains. In fact, bones and other hard structures have generally evolved to protect such internal structures from harm. But when the harm comes in the form of a sharp object, it can bypass the ribs and other protective structures to get into those theoretically protected areas.

One critical example is synovial spaces, he says. Joints are surrounded by synovial fluid which serves, in part, to keep the joints lubricated. The synovial membrane encapsulates that fluid, keeping all its components stable and balanced. But once the membrane is compromised—by a puncturing object, for example—that stability is disrupted. Fluid leaks out, and pathogens leak in, creating the potential for serious and career- and/or life-threatening infection (see #6 below).

4. Puncture Wounds Introduce Pathogens into the Body.

Piercing objects transport a host of pathogens—potentially harmful microscopic agents—into deeper tissues and structures.

“Oftentimes, the object is contaminated with soil or manure, or it’s rusty,” Pattio says. “Not to mention the fact that the horse has bacteria all over himself. It’s rarely sterile! There are lots of sources for deep infection.”

And it’s not just microscopic elements that get in there, he adds. Puncturing objects—in particular, wood splinters and fragments—can break off and remain embedded in the body.

These unwanted objects can not only instigate infection but also trigger significant inflammatory processes as the horse’s immune system reacts to the invaders.

When treated too late these reactions can be fatal, so timely attention to puncture wounds is vital, says Pattio.

5. Unexplainable Swelling Might be a Puncture Wound.

Lingering swelling could be the result of a puncture wound. That’s even more likely when the horse owner can’t find an entry wound or doesn’t recognize the depth of the wound before it heals.

“You think it’s a small prick, but then three or four days later the whole area around it has blown up,” Pattio says.

People sometimes confuse such wounds with spider bites, he adds. But the reality is that often the horse has incurred a puncture wound that has healed at the skin level, trapping in debris, pathogens, or necrotic (composed of dead cells) tissues.

6. Chronic Oozing is Likely a Puncture Wound.

Occasionally, horse skin might leak liquids of various colors, odors, and viscosities, says Pattio. These liquids might be pus from an infection, blood, blood serum, or even synovial fluid. If that liquid drains from an otherwise unexplained spot in the skin, he says, it’s quite likely to point to a puncture wound.

Sometimes, the liquid drains from a known wound, but the wound gets treated as a surface wound rather than a puncture. “You wrap it up; it heals; and then suddenly it’s draining,” he adds.  

“Puncture wounds create a tract, or fistula, and later on that tract drains,” Pattio explains. “If you see exudate dripping from the skin, you need to determine the extent of it, and get to the source of that.”

The wound needs investigation and—most likely—flushing to remove debris and infection, he says.

In some cases, when puncture wounds go unidentified for long periods of time, horses can develop what’s known as a “fistulous tract,” Pattio adds. Wound probing, flushing, resection or surgical removal of the fistulous tract, and sometimes the placement of a drainage tract can help with healing, he says.

7. Ideally, Keep the Puncture Object in Place until the Vet Arrives.

While owners might want to immediately extract an object that’s caused a puncture, that’s typically not the best choice.

In-place foreign objects can solve a lot of unknowns, including what direction the object took into the body and how deep it went, and it can also help reduce the chances that any parts of the foreign body break off and stay inside the horse, says Rosa. “Call a veterinarian, and do not do anything without proper guidance. You can make things much worse by simply trying to remove any apparent foreign object that is causing the issue.”

It’s also generally safer for the handlers if the veterinarian removes the object, because anesthesia might be necessary if the horse reacts violently to the pain.

Even so, if you and your vet determine it’s even more dangerous to leave the object in place than remove it, try to take photos before extraction, Pearson says. Be sure to keep the object nearby, without cleaning it off, to provide important information about the wound.

8. Puncture Wounds Always Require Veterinary Care.

Ideally, owners should contact their veterinarians as soon as they notice a puncture wound, Pattio says. While that might not necessarily mean a middle-of-the-night emergency visit, it at least warrants a phone call.

“Talk about the history, and by that I mean, give an idea of the object, its size, its location,” he says.

Such information can help vets determine whether an immediate farm call or referral is necessary, or if a home visit can wait until regular hours.

When the vet comes—whether it’s an emergency call or not—provide as much detail as possible. “Do you know what happened?” says Pattio. “Did you see it happen? That’s the ideal scenario. If not, give as much detail as you can.”

That detail might date back several days or even weeks—especially if the only information is a tiny scab that healed over quite some time ago, he explains. “Sometimes you’ll just be like, ‘Whoa, there was just a little scab there. I had no idea it was a puncture wound!’”

Veterinarians have several options for treating suspected puncture wounds, including antibiotics, anti-inflammatories, imaging, and exploratory and therapeutic surgery. Radiographs can be especially helpful if the foreign object or its remnants are metallic.

In general, using a sterile probe helps the veterinarian retrace the path of the puncture to provide insight into the damage the penetrating object might have caused.

9. The Challenge: Getting Puncture Wounds to Heal from the Inside Out (and Not the Reverse)

While skin damage might be the only part of the puncture wound owners see, in many ways it should be the last of their concerns—at least chronologically speaking, says Pearson. That’s because with punctures you really want to make sure that everything that needs to come out—debris, pathogens, pus—can come out. Once the internal structures are healed, skin healing can begin, she says.

“A lot of times, we don’t want to close the skin over a puncture wound because if there is any infection or any foreign body, we want to increase the likelihood of that being expelled by the body.”

“Definitely, one of the main problems with puncture wounds is the healing of the skin before the inner tissues—and that is why these types of lesions are so challenging,” Rosa adds.

10. A Keen Eye Can Help Prevent Puncture Wounds.

Horses can sustain puncture wounds no matter how much their handlers try to protect them. But there are a few steps they can take to reduce the risk, Pearson says.

“Just walk around your horse’s (stall, paddock, or pasture) and make sure there’s nothing sticking out,” she suggests. “It’s amazing how many rusty nails stick out of things, and people just don’t realize it.”

Managing horses with their welfare in mind can also reduce risk. “Most of the puncture wound cases we see in our hospital have to do with stressed horses and wooden pickets,” Rosa says. “It’s very important to work on your horses’ well-being, since this avoids most of the common accidents we see in our practice.”

When puncture wounds do occur, though, up-to-date tetanus vaccinations can prevent unnecessary complications, Pearson adds.

Take-Home Message

Puncture wounds in horses might appear to be mere flesh wounds—small and minor. But the foreign objects causing these wounds can pierce though muscles, tendons, ligaments, bones, blood vessels, synovial spaces, organs, and more, introducing pathogens that can set up infection. Close observation and early intervention, taking care not to remove the piercing object until consulting a veterinarian, can help horse owners prevent the sometimes-dire consequences of puncture wounds. Good farm maintenance and mindful horse management, prioritizing horses’ well-being, can help reduce the risk of them occurring in the first place.