One of the best ways to prevent the devastating and often deadly hoof disease laminitis is also one of the easiest, but horse owners must recognize the need and, just as importantly, act on it. Combating obesity in horses—a common contributor to insulin dysregulation, a notorious precursor to laminitis—is key to prevention, but many horse owners simply don’t recognize their horses are overweight, says Andrew van Eps, BVSc, PhD, MACVSc, Dipl. ACVIM, associate professor of equine musculoskeletal research at the University of Pennsylvania School of Veterinary Medicine’s New Bolton Center.
Van Eps spoke to a group of veterinarians and farriers about evidence-based ways to prevent and treat laminitis during the 11th annual Northeast Association of Equine Practitioners (NEAEP) symposium, held Sept. 25-28 in Saratoga Springs, New York. Besides reviewing tried-and-true, research-backed techniques, he previewed other ways we might avoid or manage laminitis in the future.
In laminitis cases the interdigitating laminae, which are the tissues that suspend the coffin bone within the hoof capsule, become damaged and inflamed. In severe cases they separate, releasing the coffin bone to rotate downward or sink. Many acutely or chronically laminitic horses must be euthanized due to the damage and relentless pain the condition causes. (Learn more from van Eps about what’s happening on a cellular level in laminitis cases here.) Veterinarians have identified three major forms of laminitis based on their underlying causes:
- Systemic inflammatory disease (infection of the blood, or sepsis) causing acute laminitis;
- Hyperinsulinemia (an endocrinopathic, or hormone-related, issue); and
- Excessive weight-bearing on a limb (supporting-limb laminitis—to which racehorse Barbaro succumbed).
Heavy Horses (and Ponies)
In one study researchers found that 40% of owners considerably underestimated their horses’ body condition. “There is this sort of body dysmorphism thing,” said van Eps. “We need to change our definition in our minds of what constitutes normal body condition in horses.”
That means not allowing horses and ponies to reach body condition scores as high as industry culture and some competition arenas have deemed acceptable—even fashionable.
The insulin dysregulation (ID)—basically, the body’s inability to respond normally to insulin release—often lurking in these obese horses commonly leads to laminitis. Van Eps said the best way to manage ID in horses and ponies is to control diet and reduce obesity. “Exercise is difficult in some of these patients,” he said, whether due to extreme lack of fitness or because the horse already has laminitis, making it painful to work. “Diet makes much more of a difference; it’s much more important.”
He recommends weighing the horse to get an accurate measurement, then feeding hay at a rate of 1.5% of the horse’s body weight per day as a reliable and simple weight loss strategy.
“(Hay) should be either tested (for nonstructural carbohydrate [NSC] levels) or soaked,” he said, because these sugars can exacerbate the condition. Also consider testing NSC after soaking (he suggested Cumberland Valley Analytical Services for testing). Supplement the hay with a ration balancer to ensure vitamin and mineral needs are met.
Keep in mind not all horses with ID are obese (or even overweight) and, also, that horses with ID might have laminitis without obvious lameness. Van Eps said that in one study researchers found radiographic evidence of laminitis in 76% of horses presented for pituitary pars intermedia dysfunction (PPID, aka equine Cushing’s disease), but half of them had not shown signs of foot pain, and laminitis wasn’t recognized by the owners. Pituitary pars intermedia dysfunction leads to an overproduction of hormones such as adrenocorticotropic hormone (ACTH) and cortisol, and affected horses can have regional fat deposits and experience muscle wasting, among other signs, but they aren’t generally obese.
“Our goal for now (to prevent laminitis in endocrinopathic horses) is to target insulin dysregulation,” he said. “Diagnose them early, because this type of laminitis is often well-advanced before we see any outward clinical signs.”
Van Eps prefers to test plasma ACTH concentration for diagnosing PPID: either resting (baseline) or after thyrotropin-releasing hormone (TRH) stimulation (a little more sensitive). With this test veterinarians look for overproduction of ACTH, which the pituitary gland—which is enlarged or affected by a tumor in PPID horses—normally makes in relatively small amounts to control the function of the adrenal glands. Veterinarians must keep in mind seasonal reference ranges when they assess results.
He says that after starting the confirmed-PPID horse on Prascend (the FDA-approved pergolide drug), “you need to test them a month later and then at least once a year to see if their ACTH is under control, because you can’t control their laminitis if there’s an underlying uncontrolled endocrinopathy.”
Van Eps recommends using the oral sugar test to check for equine metabolic syndrome, another form of insulin dysregulation. This involves collecting a blood sample, followed by administering light corn syrup orally, and collecting another blood sample 60 to 90 minutes later. In a new study van Eps’ group showed that the oral sugar test can be performed immediately after the TRH stimulation test as a combined protocol without affecting the results, and this is best way to test for ID and PPID in one visit.
He welcomes equine veterinarians to contact him with any questions about interpreting results.
Indeed, metabolically, there’s a “type” of horse or pony that is prone to developing laminitis, but they’re not always visibly obvious. Researchers are working hard, though, to identify predictors in the genes, said van Eps.
“There’s a good chance in the future that we’re going to have some genetic markers and some genetic tests,” he said, “and potentially breed this out (of the horse population).”
In terms of medical treatments for ID, van Eps said there are now options that might suit different horses and ponies, and owners should always consult their veterinarian. “Levothyroxine may be a useful adjunct to weight loss and can help to improve ID,” he told The Horse. “Supplements containing polyphenols such as resveratrol may help to improve ID; however, there is very limited evidence for this in horses at this stage.
“Metformin can be useful in horses and ponies to reduce the insulin response to feeding if given in a targeted way shortly before meals/turnout,” he added. “There are other options on the horizon for targeting ID, including a recent paper with some exciting preliminary evidence on a drug class that helps to control insulin by enhancing the clearance of glucose from the blood by the kidneys. We are likely to see more medication options become available for horses and ponies with ID in the coming years.”.
Four on the Floor
Another type of horse predisposed to laminitis is one that hasn’t been bearing weight evenly on all four limbs, usually because of a severe injury. Metabolically and mechanically, something happens in these horses that causes laminar damage in the supporting limb.
Van Eps says to prevent laminitis in these horses, blood must perfuse the tiny capillaries of the foot in the supporting limb. The best way to improve digital capillary perfusion is to cycle weight off and on that limb. That’s not easy to accomplish in a horse that’s shifting its weight to be comfortable, however.
“We need to improve limb load cycling in order to improve perfusion,” said van Eps. “We’ve done some work trying to improve perfusion using various means in the limb under load, and it doesn’t appear possible. It looks like we have to provide some sort of load relief to do that.”
He reported that veterinarians in Canada are developing a robotic sling that provides individual limb load relief rather than unloading all limbs as existing slings do.
Another approach he and other researchers have taken to unload the supporting limb is forced recumbency (lying down): putting horses in a stall or corral with a low ceiling or roof so they’re unable to stand for controlled periods. “They very calmly accept their lot,” he said of Standardbreds and ponies in which his colleagues have tested this approach for up to three days. They were able to adjust their recumbency. Van Eps said the approach “might sound ridiculous,” but knowing what he knows about laminitis, he feels it might be useful either as a preventive or in acute cases.
Other approaches involve pain relief. Giving horses systemic analgesia such as opioids can make horses sluggish, causing them to move less when, again, limb cycling is what’s desirable. Regional techniques—blocking the injured limb—might be the better answer.
“We need to get them moving,” said van Eps, but “recognizing when they are not moving enough (and laminitis is an impending threat) is half the challenge.”
He said for this effort researchers need technology to measure not only heart rate and movement in supporting-limb-laminitis-prone horses—something existing wearables can do—but also subtle offloads of the limb; pedometers on individual limbs just count the steps and tend to overestimate.
While we wait for technology to become available, said van Eps, “what protocols could we employ now? The best thing we can probably do for horses at high risk of supporting-limb laminitis is controlled walking or static load cycling, as often as every two to four hours. Forcing them or encouraging them to take some steps or at least unload that limb. I think there’s some development in that space that’s likely to be useful in actually getting rid of this problem.”
Preventing or Managing Acute Laminitis: Act Fast, Seek Ice Water Immersion
No matter the laminitis trigger in a horse, the response is the same: Don’t delay. Chill the feet. Provide pain relief.
Van Eps is known for scientifically validating cryotherapy to prevent and treat laminitis. Since doing so, he’s continued to study what’s happening in acutely laminitic horses’ hooves. “We can prevent laminitis if we get it early enough, and even in clinical situations it has been shown that cooling the feet can help prevent laminitis in horses with colitis,” he said.
Van Eps explained that the original rationale behind cooling limbs in horses at risk of or experiencing acute laminitis was blood vessel vasoconstriction in the feet, which would limit the delivery of blood-borne laminitis trigger factors ranging from endotoxin or bacteria to other compounds within the body. He cited research in which cooling scalps of human chemotherapy patients inhibited hair loss; constricting the vessels is thought to limit both chemo delivery to the follicle and follicle activity.
“Cold, though, has these really profound effects on limiting metabolic activity and limiting inflammation,” he said, as well as analgesia—reduced sensation—and enzymatic activity.
Doctors have also used cooling extensively in children with hypoxic ischemic encephalopathy (oxygen deprivation to the brain), he said—a similar condition to that seen in foals with periparturient asphyxia (so-called “dummy foals”).
Van Eps said there are also some laminitis cooling parallels with acute lung injury in systemic inflammatory response syndrome (SIRS, or sepsis) research in humans. “In rodent models of this important human disease, you end up with reduced white blood cells in the lungs of rats that are cooled, indicating that cooling can reduce the damage and inflammatory response in organs of septic animals.”
In septic horses at risk of laminitis, he’s used microdialysis probes to check glucose metabolism in cooled feet, finding indicators of energy metabolism interference in septic horses but not in septic horses whose feet were iced. “Cooling has a profound effect on slowing the metabolism of glucose in the feet, and there is some evidence that (cryotherapy) may be preventing a secondary energy crisis,” he said, “which may be one way that it helps slow the progression of laminitis in these horses.”
Even in horses with signs of acute laminitis, it’s not too late to cool the feet and help reduce disease progression. But “the hoof itself buffers heat remarkably,” he said, “so it’s a real challenge.”
One thing that’s crucial for veterinarians and horse owners to remember is that hoof surface temperature is not a good indicator of the temperature inside the hoof capsule; the hoof wall might feel quite cold to touch with some cooling approaches, but it takes immersion in an ice water slurry to cool the interior portion of the foot to the extent that laminitis can be averted or helped.
“Ice packs are convenient, and we are hopeful that with the right apparatus they might be useful,” he said. “But ice pack systems in our testing thus far have not been near as effective as ice and water immersion at cooling the actual lamellae deeper in the foot.”
Van Eps said he did some research with custom-built ice compression systems, which were very effective but expensive. “That and the ice water immersion were the most effective means,” he said.
“In general, the evidence we have suggests that the temperature within the lamellar tissue below the hoof wall needs to be less than 10 degrees C (50 degrees F)—that is the temperature that has proved effective in the experimental trials we have done.
“I do think that ice water immersion is still the way to go,” he added, “and there are commercial systems out there that are designed to allow constant ice and water immersion and that achieve similar temps to what we get experimentally.”
He recommends starting ice water immersion of the hooves of any horse immediately at risk for developing acute laminitis, such as horses with colitis, proximal enteritis, and grain overload, prior to clinical signs developing. Keep the limb immersed for as long as needed—he says horses have tolerated clinical ice water immersion for up to five days.
When do you stop icing the feet? “Use abatement of primary disease as a marker for cessation,” he said. “Along with resolution of fever and other signs of endotoxemia, blood tests such as SAA (serum amyloid A) are ways of determining if the systemic inflammation has subsided.”
Possible untoward effects of cooling the feet are increased blood viscosity, enhanced microvascular thrombus (clot) formation, impaired coagulation, enhanced edema (fluid swelling) at lower temps, and immunosuppression. But the only adverse effects veterinarians and researchers have seen with cryotherapy are dermatitis and (rarely) necrosis—frostbite—when ice has been in contact with the skin for too long.
Editor’s Note: This article is part of TheHorse.com’s coverage of topics presented at the 11th annual Northeast Association of Equine Practitioners (NEAEP) symposium, held Sept. 25-28, 2019 in Saratoga Springs, New York.