Laminitis likely can’t be cured by the time the intricate structures of the hoof degrade, it’s impossible to reverse the damage. That means that prevention, early detection and stopping progression of the disease are critical.

Responding to the slightest changes only apparent on radiographs should be acted upon, says Andrew van Eps, BVCS, Ph.D., associate professor of musculoskeletal research at the University of Pennsylvania School of Veterinary Medicine, New Bolton Center.

“A roughening of the dorsal aspect of P3 on X-ray and a change in the morphology of the tip of P3, where it turns into more like a little ski jump, these are some of the subtle changes that you see even before you see rotation,” he said.

Management practices and medication in addition to corrective shoeing play an important role in halting the progression of laminitis. The good news is that laminitis is a priority among researchers. Current studies offer promise through the appropriate implementations of therapies specifically aimed at addressing the underlying cause in different forms of laminitis.

Keep It Cool

In human research, studies show that lowering a person’s body temperature by even just 5-10 degrees below normal is effective in reducing inflammation and promoting healing. New research in equine medicine shows similar results.

There’s evidence from recent studies that show when a sick horse’s feet are cooled, they are much less likely to develop laminitis. The 2014 study, “Prophylactic Digital Cryotherapy is Associated With Decreased Incidence of Laminitis in Horses Diagnosed With Colitis,” showed that when a sick horse’s feet were consistently cooled, the horses were 10 times less likely to develop laminitis. The patients in this project were located in different hospitals and all had diarrhea.

“We can fix a lot of these sick horses now; 98% survival if they don’t founder,” Van Eps says. “But if they do founder, only half of them survived in that study. If they get laminitis, unfortunately, a lot of them can’t get back to their usage, even if it’s not severe enough to warrant euthanasia.”

Not only can cooling prevent a horse from developing laminitis, van Eps’ 2014 study, “Continuous Digital Hypothermia Initiated After the Onset of Lameness Prevents Lamellar Failure in the Oligofructose Laminitis Model,” showed that it can halt progression in horses that already had the disease.

“We really didn’t expect this to work particularly at all when we did this experiment. We thought it was too late,” van Eps says. “But it shows you how dramatic the difference can be when you cool them, even after they develop lameness.”

Given the success rate of cooling in sick and diagnosed laminitic horses, van Eps wondered if cooling could also benefit horses prone to laminitis because of endocrine dysfunction. The microscopic tissues haven’t yet been examined, but in looking at it, visually and grossly, it appeared that it had a very similar effect on the high insulin model as it has on the sick horse model.

Subtle changes you see before rotation might include a change in morphology of the P3.

“Another exciting thing about cooling is that when you cool horses’ legs and get the skin below 7 degrees Celsius or 44 degrees Fahrenheit, there is a numbing, pain-
relieving effect that perhaps we can use to our advantage in some of these cases with acute painful laminitis,” he says.

Effective methods for cooling horses’ feet are a challenge. It can be difficult to consistently maintain enough ice on the horse’s leg to effectively reduce the foot temperature. Van Eps has found that an old IV fluid bag works well and is inexpensive, but it can cause rubbing around the area you strap it on, if you’re doing it for a couple of days in a row. In his 2016 study, “A Comparison of Seven Methods for Continuous Therapeutic Cooling of the Equine Digit,” the results showed that even the worst methods dropped the temperature of the foot by at least 5 or 6 degrees, which could be beneficial.

By comparison, humans are less tolerant of cold than horses. A person can develop frostbite when near-freezing temperatures are applied over time. Occasionally, this can happen in horses.

“I think this is more likely to happen when ice is used in a boot where water is free to drain out the bottom,” van Eps says. “The ice is then in direct contact with the leg with no water interface. It is important when treating horse limbs continuously for extended periods to maintain an ice and water mixture around the limb.”

When ice melts, it’s at 0 degrees Celsius or 32 degrees Fahrenheit. When you get it out of the freezer, it’s a lot colder than that, -20 or -30 Celsius. Ice in direct contact with the leg without water mixed with it can lead to problems.

But even less than ideal applications dropped the temperature of the foot by at least 5 or 6 degrees. And that’s enough for it to be worthwhile for a horse that’s at-risk, he says.

Prevention: The Best Cure

Laminitis is always a secondary development. Whether it’s a lack of blood flow, illness or a metabolic disease, the initial issue must be addressed before the feet can be fixed.

“You can’t fix their laminitis until their underlying endocrine disease or injury is controlled,” van Eps says.

For example, a horse with insulin dysregulation needs to have this addressed with dietary management, weight loss and/or medication. A simple oral sugar test can diagnose the problem. Feed and forage are withheld overnight. The next morning, the horse is given oral sugar and its response is monitored.

“We can identify that horse and its propensity to have a problem and then deal with it with medication or management,” he says.

It starts with diet changes and can include medication such as metformin and thyroxin. There are also indications that genetics play a role in these cases. The 2017 study, “Genomewide Association Study Reveals a Risk Locus for Equine Metabolic Syndrome in the Arabian Horse,” points to genetic markers in horses with high insulin and an increased frequency of laminitis.

“If we can identify these horses genetically, that helps us keep on top of it. It also helps us potentially breed out these problems,” he says. “The Arabian industry is really good at developing ways of identifying problems genetically and screening and then breeding out a lot of these issues.”

Similarly, horses with mild lameness may be at risk of developing laminitis due to an undiagnosed case of Equine Cushing’s disease. Although the abnormality in the pituitary gland is typically associated with older horses, it can develop in horses as young as 8 and without displaying many of the classic symptoms. A blood test can measure a horse’s adrenocorticotropic hormone (ACTH) levels to determine if the horse has Equine Cushing’s disease.

“When you’ve been dealing with their feet for a long time, you’re starting to notice change. If the changes are not explainable in other ways, it’s worth testing them for Cushing’s disease,” he says. “You cannot fix their feet, get them more sound, get them going better, until their Cushing’s disease is under control.”

Pergolide is the treatment of choice for Equine Cushing’s disease and can be remarkably effective. Follow-up testing and dosing adjustments require lifelong monitoring for the best outcomes.

Managing horses with endocrine and metabolic diseases is challenging, but preventing supporting limb laminitis is a whole other level of complexity. Because researchers are beginning to understand the correlation between limb load cycling and blood flow through the foot, they are concentrating efforts monitoring the number of cycles in the horses that are most at risk.

Laminitis in the hind feet is rare, but it can happen. This can create an awkward stance with front feet behind the shoulder.

How do you increase load cycling? Van Eps explains that horses with fractured legs or high levels of pain don’t want to walk. Surgeons who repaired the leg aren’t keen on them walking around too much either.

“But anybody that’s been in the hospital and had a limb surgery, a hip replacement, a knee replacement, will know that they often get you up quite quickly and force you out of the door,” van Eps says. “I think it may be important in these equine patients that we do that to an extent.”

Slings have never been an ideal method for relieving weight off horses’ feet. The horse either dangles from the sling or wears it like a jacket, which isn’t useful either. Canadian researchers at the University of Saskatchewan are working on new sling technology that shows promise for providing intermittent weight relief.

Improvements in pain medications are also improving outcomes in preventing the development of standing limb laminitis, according to van Eps. Horses can now be given a constant rate infusion of local anesthetic to the palmar nerves. Epidurals given at the lower back of a horse are also showing promise. With the right volume of medication delivered to that spot, it’s possible to give 4-limb pain relief, he says.

Human research shows that powerful analgesic drugs don’t provide adequate relief for patients with complex pain that is present in cancer and during bone absorption. In equine laminitis patients, bone changes often begin early in the disease development, as the lamellae no longer provide suspensory support and the bone is subjected to unusual weight bearing forces, causing resorption and remodeling of the coffin bone. In humans, bisphosphonates (like Tildren and Osphos) can offer the most relief for this sort of pain.

“Reabsorption of bone is a very painful thing. The pain gets transmitted through the spinal cord and up to the brain. In a lot of these horses that have been affected for a long time, these pathways get kind of ramped up and overstimulated and that contributes to their pain,” van Eps says.

Drugs are only part of the pain management equation. Providing frog and sole support are key. Van Eps prefers correctly applied heart bar shoes that use basic farriery principles and the use of commercially available boots that allow dental impression material to be dropped into them.

“I think you can achieve some similar things and you can achieve some really great unweighting or release of pressure in horses that have particular areas of pressure with clogs,” he says.

Much to the dismay of the person cleaning a barn, van Eps regularly recom­mends bedding stalls with sand. The surface, when packed correctly, eases breakover and redistributes weight across the entire frog sole. It allows horses to pivot without catching to prevent rotational torsional force on the capsule. Some horses don’t like lying down in it, but he says that bedding half the stall with sand can alleviate this problem. It can be added to the area of the stall where the horse spends the most time—the feed tub, the water or the window. The other half can be bedded with straw or shavings and still allow the horse to lie down.

It can be difficult though to assess foot pain. A visual evaluation doesn’t always provide an accurate picture. Typically, a horse that is worse in the forelimbs will stand with its front legs in front of its shoulders, and when it’s worse in the hind limbs, the front legs will be behind the shoulders. A horse that’s evenly affected can look just “splinted.”

“Rarely do you see a horse with worse laminitis in the hind feet like that but occasionally you do,” he says. “This horse that has hind foot laminitis that was chronic and not diagnosed as a problem was presented for a neurologic evaluation. It’s unusual. You don’t see that very often.”

In horses that don’t exhibit pain from hoof testing, Van Eps applies slight rotational force to the hoof capsule, but he warns it must be done carefully.

The lucent zone on a hoof is where there is laminar separation, denoted by the deep line across the hoof.

“If they’re really severe, don’t just rotate that right off, obviously,” he says. “If you’ve been to the gym, just go easy. But you know, I think that can help you, particularly in hind feet, to establish if they’re sore or not. And then nerve blocks, you know, can obviously also help.”

Radiographs provide the most complete picture of the changes taking place inside the hoof. The digital images are so good that it’s possible to see the lucent zone and use that as a reference for measurement of lamellar lengthening or change in angle relative to the bone. X-rays are especially helpful in horses that are at high risk (e.g. overweight or with Cushing’s disease) but don’t have lameness: the images can show early signs and progression of the disease. But they must be taken regularly.

“The problem is if you’re just X-raying them for the first time, you really don’t know where that started. Serial X-rays are really important. And I find hind feet can be really deceptive on X-ray,” he says.

When treating acute laminitis, confinement and patience are the keys. “We have to be a bit patient. Because they can take more than a week to improve,” van Eps says. “But if they’re a couple weeks in and you’re not seeing improvement, I think that prognosis is very grave at that point.”

After an acute bout, once a horse begins improving, the biggest mistake van Eps sees is turning the horse out too early. He starts with keeping them stalled 1 week for every day they were lame. A horse that was lame for 5 days needs to be confined for 5 weeks.

December 2018 Issue Contents