By Andrew H. Parks, MA, Vet MB, Diplomate ACVS
My horse had mild laminitis in the past, but is rideable now. Can you tell me how to explain this disease to my friends?
Laminitis is commonly referred to as founder. The term laminitis means inflammation of the laminae. What are the laminae (also called lamellae)? The laminae are two highly folded tissue layers, one which lies on the surface of the coffin bone (called the distal phalanx by veterinarians) and one which lies on the inside of the hoof wall. By complex linking, somewhat like a very large number of dovetail joints, the laminae connect the coffin bone to the hoof wall. Laminitis results in damage to the lamellae. The cause of laminitis is much debated, but the result is cellular death, and laminar disruption. Keep in mind; this is a simplified definition of a complex problem. The clinical consequences of this damage are variable, and at one end of the scale result in mild transient foot pain, and at the other end it can result in catastrophic separation of the hoof from the coffin bone.
Laminitis is known to occur as a sequel to a variety of diseases, such as diarrhea, retained placenta and certain types of respiratory infections. Over ingestion of grain, or grass that is high in fructans (a type of sugar), may cause a gastrointestinal upset that leads to systemic disease and may similarly result in the development of laminitis. The development of laminitis is also associated with certain hormonal abnormalities, namely Equine Cushing’s Disease and Equine Metabolic Syndrome. Equine Cushing’s Disease (also referred to by veterinarians as Equine Pituitary Pars Intermedia Dysfunction) occurs when a gland at the base of the brain doesn’t function correctly. Equine metabolic syndrome is typically associated with overweight inactive horses and resembles type II diabetes in humans. There are tests that can determine if your horse has one of these two conditions. There are causes of laminitis other than those associated with systemic disease or hormonal abnormalities. There are multiple instances where injections of steroids have been implicated in the development of laminitis after the injection, and anecdotally, it appears to be related to the type and amount of steroid given. That said, the mechanism is unknown and this relationship has not been proven scientifically. Laminitis may occur in one limb following prolonged overloading secondary to non-weight bearing by the other limb though the mechanism by which this happens is also unknown. Examples of reasons for prolonged unilateral weight bearing include severe infection or trauma in the opposite limb. Similarly, it’s been well documented that horses ridden too long and too hard on roads are susceptible to "road founder." This is different from stone bruising, and it’s caused by the mechanical trauma to the laminae—the result of repeated pounding of the hoof on a hard surface.
From the different type of disease we have listed that laminitis is associated with, you shouldn’t be surprised to hear that there is most likely more than one mechanism by which the disease develops. The one we know most about is laminitis associated with eating too much grain, and other diseases like it such as diarrhea. These diseases are thought to be associated with systemic inflammation and once the inflammatory process is set in motion, this type laminitis may progress through various stages. The first is the developmental stage; you can think of this as the stage during which the disease is incubating. This length of this stage is highly variable, but can be anything from 10 to 50 hours. There are no external clinical signs, but the process has been set in motion, and is very likely to lead to the next stage. The second stage is called acute laminitis. In this stage, clinical signs are present (i.e. the horse is exhibiting lameness and heat in its feet), but the separation of the lamellae hasn’t reached the point at which the union between the coffin bone and the hoof is very unstable. This stage usually lasts several days. The third stage is called chronic laminitis. A horse enters the chronic stage after the damage to the lamellae has become so great that the attachment of the coffin bone to the hoof breaks down and the coffin bone shifts within the hoof capsule. Horses don’t inevitably progress from stage one to two, and then from two to three, but it is common for them to do so. The initial insult is followed by a repair process that attempts to restore the attachment between the coffin bone and hoof wall. In some horses in which the initial insult was mild, no changes may be seen in the horse’s feet. In others in which displacement has occurred, there are characteristic changes in the hoof that may permanently alter the way the hooves look and the way the horse’s feet function. However, it is unlikely that inside the hoof the laminae ever return to absolutely normal. The mechanism by which laminitis occurs in horses with Equine Cushing’s Disease and Equine Metabolic Syndrome is not nearly as well understood. At this time there is increasing evidence that the disease is not initiated by a primary inflammatory process. Therefore, with what we know now we can’t categorize the stages as we can with the inflammatory type of disease. Similarly, while we have hypotheses about why horses that bear all their weight on one leg develop laminitis in that leg, at this juncture, they have not been confirmed scientifically. Regardless of the cause, these horses may also develop the characteristic secondary changes to the hoof.
The symptoms in the acute phase of the disease are related to foot pain, and increased temperature of the feet. Mildly affected horses may be difficult to diagnose, but as the lameness increases there is a classic stilted gait associated with the disease. In the chronic phase of the disease, symptoms can include both changes in gait and the development of abnormally shaped hooves. In both acute and chronic cases the pain may be such that your veterinarian cannot lift a foot off the ground because the foot on the other side hurts so much. If he can pick up a foot, your veterinarian may well put hoof testers on the feet to pinpoint the pain in the foot.
Treatment for laminitis, given the different causes and the wide range of symptoms displayed, varies accordingly. As such, the treatment varies depending on the individual horse’s history, the individual experience of his veterinarian, and the severity of the disease. In addition to treating the laminitis, your veterinarian will treat any primary disease process that was thought to precipitate laminitis in your horse. For example, this may include antibiotics and fluids if your horse has diarrhea or pneumonia. Also, Equine Cushing’s Disease or Equine Metabolic Syndrome may require a specific treatment. If these other disease processes are not addressed, then the overall treatment is not likely to be successful.
In general, the treatment for laminitis can be divided into medical management and hoof care. In the acute stage of the disease, the treatment is primarily medical. Many different drugs have been tried in the treatment of laminitis, and none have definitively been found to be effective in halting the disease. However, the mainstay of treatment is usually drugs that are known to decrease inflammation and control pain. Fortunately, drugs such as phenylbutazone and Banamine do both of these. Other drugs used include DMSO, which is another anti-inflammatory drug and acepromazine, a vasodilator, which is used to attempt to restore blood supply to the foot. There are numerous other drugs that your veterinarian may deem wise to use depending on the type and severity of disease that your horse has. Your veterinarian will titrate the treatment needed based on the symptoms your horse is displaying, and will monitor your horse’s progress and adjust the medications used accordingly.
In the acute stage of the disease, hoof care may involve icing the feet, removing the shoes and supporting the ground surface of the foot. It is well established that keeping a horse’s foot cool (< 5 degrees Celsius) significantly reduces the severity of the clinical disease that will develop whether started in the developmental stage of the disease or at the beginning of the acute phase, but of course, the sooner the better. Unfortunately, the disease cannot be identified in the developmental stage so unless you know the horse has a disease that carries a high risk of causing laminitis, it is usually not started until clinical signs are evident. Veterinarians frequently will ice the feet in the acute stage of the disease, but the evidence for its effectiveness is not as compelling. You should be aware that removing the shoes of a horse is controversial. Shoes concentrate the stress of weight bearing around the outside of the foot on the wall, precisely the tissues that are most likely to be damaged. Therefore, removing shoes may reduce the concentration of stress around the perimeter of the foot. Additionally, it allows your veterinarian greater freedom in using other supporting devices. However, there is concern that pulling the shoe when the attachment of the coffin bone to the hoof is damaged that the trauma of removing the shoe will further damage the attachment. In our hospital, we usually remove the shoes if we believe it can be done without exacerbating the trauma that has already occurred, but you should be aware that it is not a clear cut decision and depends on information your veterinarian would determine at the time of examination. The easiest way to support the hoof is to have the horse stand on something that spreads its weight across the ground surface of its foot. The easiest way to do this is to stand the horse on sand. However, sand stalls are not always readily available and may come with their own issues. Alternatively, very deep bedding with shavings may be used, though this doesn’t seem to be quite as effective. Instead, veterinarians will frequently tape high density Styrofoam or a silicone putty to the bottom of the feet. Another option is to use hoof boots that have a layer of closed cell foam in the base may be used. Some horses respond immediately, whereas others may not benefit as much from this maneuver.
In horses with chronic laminitis, hoof care is the mainstay of treatment, but drugs are used for pain control, and the most commonly used of these is phenylbutazone. Once the disease process has been going a few weeks, hoof care most commonly involves some sort of shoeing. There is not space here to include an in-depth look at the different shoes used, but suffice to say that the shoeing varies with the severity of the disease process, the amount and type of displacement that may have occurred and the experience of the veterinarian/farrier team.
If your horse develops laminitis, it is an emergency, though not of the 5-minute type, and you should call your veterinarian promptly so he/she can advise you about what you should do until the horse can be seen. In general, the prognosis is related to the severity of the clinical signs that develop, because these clinical signs reflect the damage that is occurring inside the foot. Unfortunately, laminitis is a very unpredictable disease, and may take a turn for the worse at any time (in contrast, recovery is slow and sudden turns for the better cannot be anticipated). Mildly affected horses may recover quickly and return to work without any external or even radiographic evidence of the injury. Other horses are affected severely enough that rehabilitation takes many months. Yet still others are so severely affected that they are unable to move and their feet are planted to the ground and the horse may require euthanasia.
You are fortunate that you now are able to ride your horse again, because many others are not so lucky. While this may seem like a long answer to your question, it is in fact a very brief synopsis of the facts and inevitably includes some simplifications because whole volumes have been written on the development and treatment of laminitis. However, hopefully you have found it helpful, and if you want to find out more, a good starting place.
Andrew H. Parks, MA, Vet MB, Diplomate ACVS has an interest in lameness and is a professor of Large Animal Surgery at the University of Georgia.
Reviewed and updated by original author in 2016.