Laminitis has long been among the most dreaded diagnoses in the horse world, and understandably so. The destruction of the connective tissues within the foot (laminae), combined with the muscle forces that pull on the coffin bone, can separate the bone from the hoof wall. This can cause excruciating pain and often leads to permanent unsoundness. Cases may be severe enough that euthanasia is warranted to relieve suffering.
There are many treatment options proposed for laminitis. Unfortunately, most have not been tested, and many are often ineffective. The sad reality is that by the time a horse is showing the first outward signs of lameness and pain, the damage within the foot is already underway.
It’s not fully understood exactly how and why a case of laminitis develops. However, in recent years, state-of-the-art biotechnology has yielded sometimes surprising insights into the bio-molecular changes within the tissues of the foot that lead to laminitis. For example, it is now known that not all cases of laminitis begin the same way. Sometimes, laminitis is the result of inflammation that develops within the connective tissues of the foot. But in the majority of cases---about 70 percent---inflammation is not the triggering event, but the result of external forces.
With this growing knowledge, veterinarians have been able to identify with increasing precision which horses are more at risk for pasture-associated or endocrinopathic laminitis. This allows owners to target their preventive measures toward the horses who are most vulnerable to different forms of the disease.
Here are three major risk factors---along with specific steps you can take to minimize them and reduce your horse’s chances of developing laminitis.
Cause: Metabolic disorders
Many cases of pasture-associated or endocrinopathic laminitis stem from equine metabolic syndrome (EMS), a disorder that is characterized by insulin resistance, a condition in which a horse’s cells do not respond appropriately to the hormone insulin. These horses have high concentrations of insulin in the bloodstream (hyperinsulinemia), similar to type-2 diabetes in people. Exactly how hyperinsulinemia leads to laminitis isn’t known. In fact, the insulin resistance itself is likely not the cause of the condition. Researchers have shown that injecting horses and ponies with high doses of insulin can induce laminitis without insulin resistance.
Often, endocrinopathic laminitis is a low-grade chronic form of laminitis without severe rotation of the coffin bone. It tends to come on slowly, causing soreness in the feet but not necessarily extreme pain. Separation and displacement of the coffin bone may not occur, but if it does, the process is fairly gradual, not a single catastrophic event.
Fortunately, metabolic disorders in horses can be controlled, reducing the risk of laminitis, with these basic steps:
1. Identify at-risk horses. EMS is a complex disorder that is not yet fully understood. But horses prone to EMS do have several distinct characteristics. Often, they are “easy keepers,” who gain weight even with little or no grain in their diets. Many are obese or exhibit “regional adiposity”---the development of fat deposits in distinct areas---even if they are not overweight. They may be “cresty,” with fat accumulating along the crest of the neck, and may also have unusual pads of fat over the tailhead, behind the shoulders or near the sheath or mammary glands. Another sign may be distinct growth rings on the hoof walls that show previous episodes of mild laminitis. Talk to your veterinarian if your horse fits this profile; blood tests can determine if he is insulin resistant.
2. Treat PPID. Pituitary pars intermedia dysfunction (PPID, also commonly called Cushing’s disease) is a malfunction of the pituitary gland that results in excess production of the hormone cortisol. This leads to hormone imbalances throughout the body. Unlike EMS, which tends to develop while a horse is younger, PPID is more common in those over 16 years of age. However, a horse with EMS may be more likely to develop PPID at a younger age, and both conditions may occur together in some animals.
Increased susceptibility to laminitis is one of the primary concerns with PPID, which is also characterized by a heavy coat that is slow to shed out (hirsutism), increased thirst and urination (from renal hormone problems), excessive sweating, loss of muscle mass, lethargy and an increased susceptibility to infections. Exactly how PPID causes laminitis isn’t certain. Hyperinsulinemia may play a role, or it may result from high levels of a different hormone.
Consult your veterinarian if you notice any signs of PPID in your aging horse. PPID can be controlled with the drug Prascend. The active ingredient in Prascend is pergolide and is formulated for consistent absorption in horses.
3. Minimize sugars and starches in the diet. Even small or “normal” portions of grains, molasses, sweet feeds and other sources of sugars and simple starches, also called nonstructural carbohydrates (NSCs), may trigger laminitis in horses with metabolic disorders. You’ll want to limit or eliminate concentrates, especially if your horse is overweight.
If your horse is not overweight and needs extra calories to maintain his condition, look for a feed that derives calories from fat, not NSCs. A number of low-sugar feeds are available that are formulated for horses at risk of laminitis. Breaking up the ration into multiple small meals served throughout the day can help avoid wide fluctuations of glucose and insulin in the blood. Also be careful of treats---a number of seemingly “healthy” treats for horses can be high in sugar.
4. Limit access to lush pasture. Grazing lush pasture grasses, which are rich in a sugar called fructan, is a well-established cause of laminitis in at-risk horses. Fructan levels tend to peak in spring and fall but can fluctuate throughout the year. Sending a grass sample to a laboratory for analysis is the surest way to be certain of it sugar content. Your veterinarian or a local extension agent can help you locate a suitable facility and understand the results. Testing your grass periodically throughout the year, in different seasons and climatic conditions, can help you identify patterns in the fructan levels in your pasture.
How much grazing is “too much” depends on the individual horse. Knowing what your pasture fructan levels are, and how and when they vary, your veterinarian can help you develop a turnout schedule that suits your horse’s needs. You may need to use a grazing muzzle to limit his intake during peak periods of grass growth or, if your horse is especially vulnerable, the only safe form of turnout may be in a year-round dry lot.
Hays, too, can have varying levels of fructan. Cool-season grasses and hays, such as fescue, rye and bluegrass, tend to be higher in sugar than warm-season grasses such as Bermuda or switchgrass. If your horse’s dietary needs are strict, you may need to send samples from every new load to a laboratory for testing. An all-hay diet with a low-calorie ration balancer or a vitamin and mineral supplement is safest for a horse whose NSC intake must be closely controlled.
5. Manage body weight. If a horse is overweight, taking steps through both diet and exercise to take off the extra pounds can improve his insulin sensitivity and reduce the risk of metabolic laminitis. Reducing or eliminating concentrates and keeping the horse on a grass hay-based diet will help with weight loss, but also talk to your veterinarian about a safe exercise regimen for your horse, especially if he’s older and/or has already experienced bouts of laminitis. Maintaining a healthy weight also reduces the mechanical burden on a horse’s feet.
Cause: Systemic Inflammation
Probably the most thoroughly studied causes of laminitis are localized inflammatory events that become systemic, meaning bacteria and/or their toxins spread throughout the horse’s body via the bloodstream. The source of the inflammation can be almost any organ, but it often begins in the intestine, after a horse binges on grain; the uterus, if a mare retains placental membranes after giving birth; or the lungs, after severe pleuro-pneumonia. Serious gastrointestinal illnesses, such as enteritis or Potomac horse fever, can also bring on inflammatory laminitis, as can exposure to black walnut shavings in bedding.
Inflammatory laminitis is less common than pasture-associated, but the cases tend to be faster acting, intensely painful and more severe (acute). Within days, a horse can progress to complete separation of the coffin bone from the hoof wall.
The most effective measures for preventing inflammatory laminitis are well known:
6. Prevent starch overloads. If any horse eats more starch or sugars than his stomach can digest all at once, the excess nutrients pass into the intestine and hindgut, where they ferment and produce byproducts that trigger inflammation in the gut wall and ultimately can lead to laminitis. This is the well-known “breaking into the feed bin” scenario, but it can also happen to horses who are fed large grain meals. If your horse needs a lot of calories to maintain his weight, break up his ration into as many small meals as you can manage to feed him throughout the day so that he never consumes too much at once. Feeding hay first, and then the grain, can fill his stomach with fiber, which will slow the grain down so it can be digested more thoroughly. Better yet, if you need a high-energy feed, look for one that provides more calories from fat than from starches.
7. Make dietary changes gradually. Sudden changes in a horse’s diet can disrupt the intestinal flora---the populations of “good” bacteria that aid digestion, immunity and other functions---which can lead to laminitis. When introducing any new feed, including hay, start by blending only a small amount into the horse’s existing feed, then gradually increase the proportion of new to old over the course of at least a week.
8. Avoid black walnut shavings in bedding. Simply standing on wood shavings that contain as little as 20 percent black walnut (Juglans nigra) wood can induce acute laminitis within eight hours. Because this threat is well known, bedding products made for horses are almost certainly free of black walnut shavings. But if you’re buying bulk hog fuel or wood shavings from local suppliers, make sure they understand that you cannot use any product that contains black walnut. Black walnut wood has a dark brown color that stands out against lighter woods.
9. Watch for laminitis when treating other illnesses. If your horse develops a serious septic illness, laminitis will be only one of your worries. Nevertheless, as you care for your horse, it’s important to monitor his feet for the first hints of pain. The prognosis for recovery from acute laminitis depends heavily on how early treatment begins. You want to intervene and slow or halt the progress of the disease before the coffin bone rotates away from the hoof wall.
Icing the feet is currently the one method that has been demonstrated to slow inflammation and reduce the damage to the laminae, even after a horse has begun developing laminitis. Your veterinarian may also opt to pack shock-absorbing padding under the soles of your horse’s feet with the goal of supporting the coffin bone in place until the damaged laminae can heal.
Cause: mechanical stresses
Unusual stresses on a horse’s feet can bring on a case of laminitis. The primary example of this scenario is the horse who must bear a disproportionate amount of weight on one leg after an injury, then develops laminitis in his “good” foot. Exactly why weight-bearing leads to laminitis isn’t well understood, but the current hypothesis is that standing or leaning for too long on one leg compresses the blood vessels in the foot and inhibits circulation, which in turn starves the connective tissues of oxygen.
Preventing weight-bearing laminitis isn’t always possible, but reducing the mechanical stresses on your horse’s feet will go a long way toward keeping them healthy and strong:
10. Take care of the "good" hoof. If your horse sustains a serious leg injury, your veterinarian and farrier will work with you to support and protect the uninjured one as well, with wraps or Styrofoam supports underneath the sole. Be sure to follow any instructions your veterinarian offers for the uninjured leg as well as for the other, and be on alert for early signs of heat and pain. As soon as the injury allows, even light hand-walking will help support circulation in all of your horse’s legs.
11. Keep up with regular hoof trims. Overgrown or unbalanced hooves are another source of mechanical strain on the laminae. The long-toe, low-heel configuration increases the constant downward pull of the coffin bone so that even minor laminitis episodes can develop catastrophic detachments. Maintaining a regular schedule with your farrier will help keep your horse’s feet healthy and strong.
12. Go easy on hard footing. “Road founder,” a breakdown within the hoof that can occur after prolonged, fast work on hard surfaces, isn’t common. But horses who are already experiencing low-grade laminitis may be prone to more serious laminitic failure after working on pavement or hardened ground. Ideally, you want to ride on footing that’s neither too hard, nor too soft. When you do encounter pavement or hard, rocky footing, stick to a walk.
This article first appeared in EQUUS issue #439.