Equine laminitis is by far the most destructive and debilitating disease of the horse. There are many forms and causes of equine laminitis and one of the more common is Equine Metabolic Syndrome (EMS). This is a relatively new term that describes a subset of high-risk horses. These horses are characterized by 1.) insulin resistance (IR), 2.) obesity and/or fat deposits, 3.) and the presence of laminitis.
EMS is common in pony breeds, Morgan horses, and Paso Fino horses; however, EMS can affect any breed. Horses with EMS are usually identified as "easy keepers” and historically have not required much feed/energy to maintain weight. A very common physical trait of these horses is the presence of fat deposits in abnormal places. For example, the neck, tail head, and the sides over the ribs. Unfortunately, many of these horses go unnoticed until it is too late and laminitis has already set in.
The exact mechanism is not fully understood, but it has been well documented that high insulin levels in the blood lead to laminitis episodes in the horse. When horses graze on lush pasture, it results in an increase concentration of glucose in the bloodstream. In the normal horse, an increase in glucose will respond by a slight elevation of insulin until the blood glucose levels are normal. However, in the EMS horse, the body doesn’t respond like it should to the insulin and much more is released as a result. This sets up a dangerous cascade of events for the horse.
It is recommended to do a simple blood insulin and glucose ratio test on any horses that display the characteristics described. Blood should be drawn following a night of fasting and recommended 12 hours off of grass pasture. This is a useful screening test because high serum insulin concentrations are detected in horses with moderate to severe IR. It is important to know the reference range of the lab when evaluating the results. At the Rood and Riddle Lab, the upper limit of the insulin reference range is 36 μU/mL and anything above this to be suggestive of IR. The pain and stress associated with laminitis can elevate resting serum insulin concentrations from 100 to 400 μU/mL in horses and ponies with clinical laminitis. Therefore, we recommend reevaluation and repeat blood work of these patients several weeks later after the pain of laminitis has subsided.
By far, diet and exercise of these horses is going to be most essential to managing their disease. Horses should be fed according to their individual metabolic needs. Obese horses do not need concentrate feeds and can be placed on a simple diet of hay and a vitamin/mineral supplement. We recommend restricting the horse’s caloric intake until the ideal body condition for that individual horse has been reached. Obese horses should be fed enough hay to meet their energy needs, which is usually equivalent to 1.5 to 2.0 % of body weight (15 to 20 lbs hay for a 1000¬lb horse). EMS horses should be fed hay with a low (< 12%) nonstructural carbohydrate (NSC) content. NSC’s include simple sugars, starch, and fructans. We recommend soaking the hay in cold water for 30 minutes to lower the sugar content prior to feeding. Ideally, the hay should be analyzed before feeding and grass or alfalfa hay can be fed as long as NSC content has been measured. There are many commercial feeds on the market now that offer low NSC complete feeds. It is important to supplement with a vitamin/mineral to ensure the horse is getting the necessary nutrition through this process. These horses should be pastured on a "dry lot” or wear a grazing muzzle. Patients that are laminitic should not be exercised until hoof structures have stabilized, but unaffected horses should be exercised regularly. Ideally, horses with EMS should be walked on a lead rope, exercised on a lunge line, or ridden every day for ~20 minutes.
The largest source of sugar in the horse’s diet is often pasture grass. This is difficult to manage because the NSC content varies between geographical regions and depends on soil quality, climate, daylight, and grass species. Season change also causes variation in NSC of pasture grass. We recommend that access to pasture be restricted or eliminated for EMS horses. Some basic rules for decreasing the risk of pasture ¬associated laminitis are to avoid grazing when: the grass is growing quickly and is lush, the grass is first starting to dry out, the grass is growing rapidly after a summer rain, the grass is entering winter dormancy in the late fall. Generally speaking, the EMS horse should not be on pasture whenever the grass is going through a dynamic phase.
Medical management of these horses during a laminitic episode is very important. During the acute phase, managing the horse's pain, supporting the hoof, and controlling the insulin levels in the blood are critical to the horse’s survival. Pain management is often provided through non-steroidal anti-inflammatory medications such as Bute (phenylbutazone) or Banamine (flunixin meglumine). However, selective COX 2 inhibitors such as EquioxxÒ (firocoxib) may also be used for pain management in hopes of reducing the harmful effects on the GI tract and kidneys. A recent study by Dr. Nicholas Frank out of University of Tennessee has shown Thyro-LÒ (levothyroxine sodium), when given to obese insulin resistant horses helps weight loss and increases insulin sensitivity. Additionally, the human drug metformin, previously used for type two diabetes, has recently been added to the list of potential helpful medications for insulin resistant horses. Metformin has been shown to increase the sensitivity of insulin but has poor bioavailability (the measure of the amount of drug that is actually absorbed from a given dose) in the horse. Current dosing for metormin is 15mg/kg twice daily but a recent study by Dr. Jaime L. Hustace out of Oregon State University suggests a higher dose may be necessary due to the poor bioavailability of the drug. It has also been suggested that dietary supplements that contain chromium and magnesium may increase the sensitivity of insulin. Most supplements geared toward the EMS horse will have these components. Recently, researchers have found omega-3 fatty acids to have a helpful effect on regulating blood insulin levels in humans and may have a similar positive effect on horses.
Hoof care and management of the EMS horse can be extremely difficult. We recommend taking radiographs (X-rays) of the affected limbs in order to determine the alignment of the coffin bone within the hoof capsule. This will better help the farrier and the veterinarian determine their plan for trimming/shoeing. Often, during the acute phase, the feet are simply trimmed and placed in soft rubber boots if there is little or no rotation of the coffin bone on the radiographs. However, if there is significant coffin bone rotation, therapeutic shoes may be necessary. Typically these would be a shoe with a wedged heel and the breakover of the shoe set under the pillars of the toe. In addition, digital support with impression material under the frog/back half of the foot would be applied. In many cases, these horses can return to being barefoot with correct management.
In conclusion, the Equine Metabolic Syndrome horse can be maintained with proper medical management, diet, exercise, and routine hoof care.